Urban Climatic Map and Standards for Wind Environment - Feasibility Study
FINAL REPORT
C U H K
Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
TABLE OF CONTENTS
LIST OF FIGURES ...... 8 LIST OF TABLES ...... 16 GLOSSARY ...... 19 ACRONYMS ...... 21
INTRODUCTION: THE URBAN CLIMATIC MAP AND STANDARDS FOR WIND ENVIRONMENT - FEASIBILITY STUDY...... 23
PART I: URBAN CLIMATIC MAP (UC-MAP) ...... 25 PART I(A): URBAN CLIMATIC MAP (UC-MAP) ...... 26 PART I(A)-1 INTRODUCTION ...... 26 1.1 DEFINITION OF UC-MAP ...... 27 1.2 STATE-OF-THE-ART OF UC-MAP ...... 28 1.3 MODUS OPERANDI OF UC-MAP ...... 30 PART I(A)-2 DESKTOP STUDIES ...... 33 2.1 OVERVIEW ...... 33 2.2 CASE STUDY I – STUTTGART, GERMANY ...... 35 2.3 CASE STUDY II – KASSEL, GERMANY ...... 45 2.4 CASE STUDY III – TOKYO, JAPAN ...... 53 2.5 A SUMMARY OF GENERAL LESSONS LEARNT FROM CASE STUDIES ..... 62
PART I(B): URBAN CLIMATIC ANALYSIS MAP FOR HONG KONG ...... 64 1.1 INTRODUCTION ...... 64 1.2 KEY ANALYSIS ...... 85 1.3 UC-ANMAP AND PET ...... 86 1.4 DATA COLLECTION AND PROCESSING ...... 88 1.5 LAYERS AND THE CLASSIFICATION SYSTEM ...... 89 1.6 FINAL UC-ANMAP ...... 170 1.7 DESCRIPTIONS OF THE UC-ANMAP ...... 172 1.8 CALIBRATION AND VERIFICATON OF THE UC-ANMAP ...... 173 1.9 UPDATING OF UC-ANMAP ...... 177 1.10 UC-ANMAP IN GIS FORMAT ...... 179 1.11 FUTURE WORK ...... 179
PART I(C): URBAN CLIMATIC PLANNING RECOMMENDATION MAP FOR HONG KONG ...... 180
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
PART I(C)-1 INTRODUCTION ...... 180 1.1 INTRODUCTION ...... 180 1.2 PURPOSE OF THE UC-REMAP ...... 180 1.3 STATE OF THE ART OF FORMULATING THE UC-REMAP ...... 181 1.4 MODUS OPERANDI OF UC-REMAP FOR HONG KONG ...... 181 PART I(C)-2 DESKTOP STUDY FOR UC-REMAP ...... 183 2.1 CASE STUDY – STUTTGART, GERMANY ...... 183 2.2 CASE STUDY– TOKYO, JAPAN ...... 186 2.3 LESSON DRAWING FROM CASE STUDIES ...... 192 PART I(C)-3 METHODOLOGY OF THE UC-REMAP FOR HONG KONG ...... 193 3.1 PROCESS AND A PARAMETRIC UNDERSTANDING ...... 193 3.2 KEY ISSUES AND ANALYSIS ...... 206 3.3 UC-REMAP – STRATEGIC AND DISTRICT PLANNING RECOMMENDATIONS ...... 208 3.4 A GENERAL COMMENTARY AND NOTES OF THE UC-REMAP ...... 213 3.5 FOUR DESIGNATED AREAS ...... 215 3.6 BEYOND THE FOUR DESIGNATED AREAS (FOCUSED AREAS) ...... 219 3.7 LIMITATIONS AND CARE IN READING, INTERPRETING AND USING THE UC-REMAP ...... 220 3.8 STRATEGIC PLANNING IMPLICATIONS OF THE UC-REMAP ...... 221 3.9 UPDATING & MANAGEMENT ...... 222 3.10 FUTURE WORK ...... 222
PART I(D): SUMMARY ...... 223 1.1 BACKGROUND ...... 223 1.2 DESKTOP STUDIES ...... 223 1.3 STATE-OF-THE-ART OF UC-MAP ...... 224 1.4 UC-ANMAP FOR HONG KONG ...... 224 1.5 METHODOLOGICAL BASIS OF UC-ANMAP ...... 225 1.6 DESKTOP STUDIES ON WIND DATA ...... 226 1.7 WIND INFORMATION LAYER FOR HONG KONG ...... 227 1.8 FINAL URBAN CLIMATIC ANALYSIS MAP FOR HONG KONG ...... 229 1.9 BACKGROUND AND PURPOSE OF URBAN CLIMATIC PLANNING RECOMMENDATION MAP ...... 231 1.10 OVERSEAS EXPERIENCE OF UC-REMAP AND KEY LESSONS LEARNT . 231 1.11 KEY PARAMETRIC UNDERSTANDING OF URBAN CLIMATE RELATED PLANNING PARAMETERS FOR RECOMMENDATIONS ...... 232 1.12 A COMPARISON OF RECOMMENDATIONS ...... 234
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
1.13 THE UC-REMAP FOR HONG KONG ...... 235 1.14 URBAN CLIMATIC MAPS AND HONG KONG PLANNING FRAMEWORK 237 1.15 LIMITATIONS AND CARE IN READING, INTERPRETING AND USING THE UC-REMAP ...... 238 1.16 UPDATING STRATEGY ...... 239 1.17 FUTURE WORKS ...... 239
PART I: APPENDICES ...... 240 APPENDIX 1: SELECTED UC-MAP STUDIES AROUND THE WORLD ...... 241 APPENDIX 2: AN EXAMPLE OF DATA PROVIDED BY HKO – WIND SPEEDS AND DIRECTIONS BY MONTH OF THE 40 HKO STATIONS FOR THE STUDY ...... 267 APPENDIX 3: AN EXAMPLE OF DATA PROVIDED BY HKO – WIND SPEEDS AND DIRECTIONS BY HOUR (JANUARY) OF THE 40 HKO STATIONS FOR THE STUDY ...... 268 APPENDIX 4: TWO EXAMPLES OF WIND ROSES BY HKO ...... 269 APPENDIX 5: EXPERT EVALUATION ON SEA AND LAND BREEZES OF HONG KONG DURING DAY TIME AND NIGHT TIME RESPECTIVELY ...... 270 APPENDIX 6: A COMPARATIVE STUDY OF SELECTED HKO OBSERVED AND MM5/CALMET MODEL WIND ROSES – SUMMER (JUN-AUG) ...... 271 APPENDIX 7: A COMPARATIVE STUDY OF SELECTED HKO OBSERVED AND MM5/CALMET MODEL WIND ROSES – ANNUAL ...... 274 APPENDIX 8: THE RELATIONSHIP BETWEEN BUILDING VOLUME DENSITY (%) AND FLOOR AREA RATIO …………………………………………277
PART II: WIND TUNNEL BENCHMARKING STUDIES ...... 278 PART II(A): METHODOLOGY OF AREA SELECTION FOR BENCHMARKING ...... 279 PART II(A)-1 PURPOSE ...... 279 PART II(A)-2 INTRODUCTION...... 279 PART II(A)-3 OBJECTIVE ...... 280 PART II(A)-4 METHODOLOGY ...... 280 4.1 CLIMATIC AND WIND PARAMETERS ...... 280 4.2 TOPOGRAPHICAL AND EXPOSURES PARAMETERS ...... 282 4.3 URBAN MORPHOLOGICAL PARAMETERS ...... 283 4.4 BENCHMARKING AREA SELECTION ...... 290
PART II(B): WIND TUNNEL BENCHMARKING STUDIES RESULTS ...... 293
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
PART II(B)-1 INTRODUCTION ...... 293 1.1 THE STUDY ...... 293 1.2 DATA SUMMARY ...... 295 1.3 REMARKS ...... 312 PART II(B)-2 THE SUMMARY OF THE WIND TUNNEL TESTS FOR STUDY AREAS ...... 312 2.1 CAUSEWAY BAY ...... 312 2.2 SHEUNG WAN ...... 313 2.3 MONG KOK ...... 315 2.4 TSIM SHA TSUI ...... 316 2.5 TSUEN WAN ...... 318 2.6 SAN PO KONG ...... 320 2.7 TUEN MUN ...... 321 2.8 SHA TIN ...... 323 2.9 TSEUNG KWAN O ...... 325 2.10 WONG CHUK HANG ...... 327
PART III: ESTABLISHMENT OF WIND PERFORMANCE CRITERION ...... 329 PART III(A):VENTILATION FOR URBAN THERMAL COMFORT ...... 330 PART III(A)-1 BACKGROUND AND LITERATURE BASIS ...... 330 PART III(A)-2 USER THERMAL COMFORT SURVEYS ...... 337 PART III(A)-3 THE NEED OF WIND FOR URBAN THERMAL COMFORT...... 339 PART III(A)-4 FURTHER URBAN CLIMATIC UNDERSTANDING OF URBAN THERMAL COMFORT ...... 341
PART III(B): BENCHMARK STUDIES ...... 344 PART III(B)-1 INTRODUCTION ...... 344 PART III(B)-2 WIND TUNNEL TEST RESULTS ...... 344 PART III(B)-3 REMARKS ON THE BENCHMARKING TESTS RESULTS ...... 365 PART III(B)-4 POSSIBLE IMPACT OF THE MISMATCH ...... 366
PART III(C): WIND PERFORMANCE CRITERION ...... 369 PART III(C)-1 THE WIND PERFORMANCE CRITERION FOR HONG KONG ...... 369 PART III(C)-2 MPLICATIONS ...... 378 PART III(C)-3 REVIEW DURATION AND MECHANISM ...... 380 PART III(C)-4 FURTHER STUDIES ...... 382
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
PART III: APPENDICES ...... 383 APPENDIX 1: PHYSIOLOGICALLY EQUIVALENT TEMPERATURE ...... 384 APPENDIX 2: FURTHER UNDERSTANDING OF PET 28oC ...... 387 APPENDIX 3: DATA OF ANNUAL AND SUMMER MONTHS VRw AND Vp ...... 388 APPENDIX 4: THE SITE WIND AVAILABILITY VS THE SITE MEAN WIND SPEED ...... 408 APPENDIX 5: ANALYSIS OF WIND SPEED DISTRIBUTION ...... 409
PART IV: REFINEMENT OF AIR VENTILATION ASSESSMENT SYSTEM ...... 410 PART IV(A): INTRODUCTION AND REVIEW ...... 411 PART IV(A)-1 CURRENT AVA SYSTEM ...... 411 PART IV(A)-2 AN EXPERT REVIEW OF AVA STUDIES COMPLETED UNDER THE CURRENT AVAS ...... 412 PART IV(A)-3 KEY FINDINGS RELEVANT TO THE REFINEMENT OF AVAS ...... 418 PART IV(A)-4 INTERNATIONAL BEST PRACTICE – USEFUL AND RELEVANT CODES AND STANDARDS ...... 419
PART IV(B): THE REFINED AVAS AND RATIONALE ...... 420 PART IV(B)-1 REVIEW OF THE AVA TECHNICAL CIRCULAR NO.1/06...... 422 PART IV(B)-2 THE REVISED HKPSG ...... 423
PART IV(C): IMPLEMENTATION MECHANISM FOR THE REFINED AVAS..... 424 PART IV(C)-1 PURPOSES ...... 424 PART IV(C)-2 THE IMPLEMENTATION OF CURRENT AVAS SINCE 2006 ...... 424 PART IV(C)-3 IMPLEMENTATION MECHANISM FOR REFINED AVAS ...... 425 PART IV(C)-4 AUTHORITIES AND TIMEFRAME OF IMPLEMENTATION ...... 427 PART IV(C)-5 REVIEW AND MONITORING ...... 428
PART IV(D): SUMMARY ...... 429 1.1 OBJECTIVES ...... 429 1.2 KEY STUDY FINDINGS ...... 429 1.3 LESSONS LEARNT FROM AN EXPERT REVIEW ...... 429 1.4 THE NEED OF A QUANTITATIVE YARDSTICK ...... 429 1.5 SCOPE OF APPLICATION OF THE AVA SYSTEM ...... 429 1.6 KEY REFINMENTS TO THE AVAS ...... 429 1.7 NEW HKPSG CHAPTER ...... 430 1.8 IMPLEMENTATION MECHANISM ...... 430
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
1.9 REVIEW AND MONITORING ...... 430
PART IV: APPENDICES ...... 431 APPENDIX 1: HOUSING, PLANNING AND LANDS BUREAU AND ENVIRONMENT, TRANSPORT AND WORKS BUREAU TECHNICAL CIRCULAR NO. 1/06 ON AIR VENTILATION ASSESSMENTS ...... 432 APPENDIX 2: A SUMMARY OF PROJECTS ON PLANNING DEPARTMENT AVA REGISTER AS OF SEPTEMBER 2010 ...... 447 APPENDIX 3: THE PROPOSED AMENDMENTS TO THE TECHNICAL CIRCULAR FOR AVA ...... 448 APPENDIX 4: REVISIONS PROPOSED FOR HKPSG ...... 466 APPENDIX 5: WIND PROFILE...... 499
REFERENCES ...... 500
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
LIST OF FIGURES
Figure I-1 UC-Map around the world...... 29 Figure I-2 A map of OZP coverage of Hong Kong (as at 4.5.2012) ...... 32 Figure I-3 Desktop studies on selected international cities ...... 33 Figure I-4 Air path analysis map for Munich, Germany ...... 34 Figure I-5 City of Stuttgart ...... 36 Figure I-6 Development of Stuttgart in the last 100 years...... 37 Figure I-7 German Federal Building Law ...... 38 Figure I-8 The Team of the Department of Urban Climatology in Stuttgart ...... 39 Figure I-9 Thermal map of the Stuttgart city area in the evening situation (averaged) ...... 40 Figure I-10 Average daily wind velocity for Stuttgart city area ...... 40 Figure I-11 CD-ROM ―City climate 21‖ ...... 40 Figure I-12 Climate Atlas produced by the Stuttgart Regional Federation for the territory of the federation and the bordering parts of the Middle Neckar Region ...... 41 Figure I-13 Example of a climate analysis map for Stuttgart city areas ...... 42 Figure I-14 Example map with recommendations for planning for Stuttgart city areas ...... 43 Figure I-15 Climate Booklet for Urban Development, Reference for Zoning and Planning, by Office for Environmental Protection, City Stuttgart ...... 44 Figure I-16 Monthly average of the minimum and maximum daily temperatures (o C) for Kassel, Germany ...... 46 Figure I-17 Pictures for City of Kassel, Germany ...... 46 Figure I-18 Structures and methods for thermal comfort zoning ...... 48 Figure I-19 First version of UC-AnMap of Kassel Created in 1990 by Prof. Lutz Katzschner ...... 48 Figure I-20 GIS calculations and classifications for UC-AnMap ...... 49 Figure I-21 Land use map [left], thermal condition map [middle], UC-ReMap [right] ...... 49 Figure I-22 UC-AnMap for Kassel city [left] and for southwest of Kassel [right] ...... 50 Figure I-24 UC-ReMap for Kassel (Katzschner, 2005) ...... 51 Figure I-25 Normal temperatures in Tokyo ...... 54 Figure I-26 Normal rainfall and relative humidity in Tokyo ...... 54 Figure I-27 High density, high rise urban development in Tokyo ...... 54 Figure I-28 CASBEE for new construction and CASBEE – HI in Japan ...... 56 Figure I-29 Thermal Environment Map for Tokyo ...... 57 Figure I-30 Legends and Explanations for Thermal Environment Map ...... 58 Figure I-31 Tokyo Midtown Project (Roppongi) ...... 60 Figure I-32 Redevelopment of the Osaki Station West Exit A zone ...... 61 Figure I-33 Shinagawa ...... 61 Figure I-34 Locations of HKO weather stations ...... 66
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure I-35 An understating of Max., Mean and Min. air temperature of Hong Kong from January to December based on HKO data ...... 66 Figure I-36 An example of wind roses provided by HKO ...... 70 Figure I-37a An understanding of the territorial wind conditions based on annual wind roses of HKO stations – with topography background ...... 74 Figure I-37b An understanding of the territorial wind conditions based on summer (July) wind roses of HKO stations – with topography background ...... 75 Figure I-38a An example of wind roses (MM5 simulation) provided by HKUST ...... 77 Figure I-38b An understanding of the territorial wind conditions based on annual (2004) wind roses of HKUST MM5 simulations – with topography background ...... 78 Figure I-38c An understanding of the territorial wind conditions based on the July (2004) wind roses of HKUST MM5 simulations – with topography background ...... 79 Figure I-39a 3D Topography of Hong Kong...... 80 Figure I-39b Contour of topography of Hong Kong ...... 81 Figure I-40a A typical densely built urban area in Hong Kong ...... 82 Figure I-40b A part map of Building Volume understanding of urban Hong Kong based on the building data from PlanD ...... 83 Figure I-41 The Map of Greeneries in Hong Kong based on NVDI image ...... 84 Figure I-42 The relationship between PET and the urban climatic factors (Air Temperature and Wind Speed) ...... 87 Figure I-43 An Illustration of Workflow for Creating the UC-AnMap (100m x 100m raster based) . 88 Figure I-44 SVF classification of Tsim Sha Tsui ...... 94 Figure I-45 Building Volume Map ...... 96 Figure I-46 Topographical Height Map...... 98 Figure I-47 Green Space Map ...... 101 Figure I-48a Components of Thermal Load Map ...... 102 Figure I-48b Layer of Thermal Load of the UC-AnMap ...... 103 Figure I-49 Relationship between Gross Building Coverage Ratio and Wind Velocity Ratio ...... 105 Figure I-50 Creation of Ground Coverage Map using GIS ...... 106 Figure I-51 Ground Coverage Map ...... 107 Figure I-52 Natural Landscape Map ...... 110 Figure I-53 Proximity to Waterfront Map ...... 113 Figure I-57 Proximity to Open Space Map ...... 115 Figure I-55 Slope Map...... 117 Figure I-56 Proximity to Openness Map ...... 118 Figure I-57a Components of Thermal Load Map ...... 119 Figure I-57b Dynamic Potential Map of the UC-AnMap ...... 120
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure I-58: Hong Kong‘s location and its satellite image…………………………………………. 121 Figure I-59: Desktop studies on Stuttgart (Germany) and Tokyo (Japan)………………………….. 122 Figure I-60: An example of wind information as in the Guideline VDI 3787, Part1………………. 123 Figure I-61: The location of Stuttgart in Germany and its surrounding topography……………….. 124 Figure I-62: The measured wind roses in Stuttgartz………………………………………………... 125 Figure I-63: (a) calculation result and (b) synthetic wind roses generated with DIWIMO………… 126 Figure I-64: (a) the evaluated air-flow patterns in Stuttgart, Germany; (b) evaluated preserved areas in Stuttgart for fresh cool air flowing to the city centre (Baumüller et al., 1992b)…. 126 Figure IB-65:(a) Ventilation zone as green area in the land use plan; (b) Ventilation zone as green area in the local development plan (Baumüller, 2006)…………………………………… 127 Figure IB-66: (a) Ventilation zone in an aerial photo; (b) current view of the ventilation corridor in Vaihingen; (Reuter, 2008) 128 Figure I-67: The location of Tokyo and Tokyo Metropolitan‘s 23 wards…………………………... 128 Figure I-68 (a) Map of Wind roses at near ground level; (b) Prevailing wind directions (measured by Japan Meteorological Agency in Aug.1998-1999)…………………………………...... 130 Figure I-69: Example of major air paths in Minato-ku ward, Tokyo……………………………….. 131 Figure I-70: Evaluated wind information of Tokyo Metropolitan areas……………………………. 131 Figure I-71: 3 Types of Kaze-no-michi (ventilation paths) , which brings cool sea breezes into urban areas (AIJ, 2008)………………………………………………………………………. 132 Figure I-72: Locations of HKO weather stations……………………………………………………. 133 Figure I-73: Summer-July wind roses of HKO stations – with topography background…………… 135 Figure I-74: Annual wind roses of HKO stations – with topography background………………….. 135 Figure I-75: An understanding of the territorial wind conditions based on seasonal wind roses of HKO stations – with topography background (1998-2007 Jun-Aug)………………………... 136 Figure I-76: An example of wind roses (MM5/CALMET simulation) provided by HKUST………. 139 Figure I-77: Prevailing summer (2004 Jun-Aug) wind directions based on MM5/CALMET simulation – with topography background…………………………………………….. 139 Figure I-78: An understanding of the territorial wind conditions based on summer wind roses of MM5 simulation – with topography background (2004 Jun-Aug)……………………………140 Figure I-79: An understanding of Monsoon circulations in eastern and southern Asia…………….. 141 Figure I-80: Seasonal mean wind directions (Yan, 2007)……………………………………………142 Figure I-81: Wind roses of WGL (Annual and Summer)…………………………………………… 143 Figure I-82: An understanding of the daily mechanism of Land and Sea breezes. Note the common onset time of the sea breezes at just before noon (Simpson, 1994)……………………. 144 Figure I-83: An understanding of the Land and Sea Breezes……………………………………….. 145 Figure I-84: Two scales of sea breezes……………………………………………………………… 145 Figure I-85: Dominant wind direction observed at surface anemometer stations…………………... 146 Figure I-86: Sea breeze simulation for 10 Dec 1990 (wind at 10m above terrain)…………………. 146
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure I-87: An expert understanding of the sea breezes at the western territory of Hong Kong on Nov 2007 under weak background wind, after K K Yeung, 2007...... 147 Figure I-88: 24 hourly variation of wind field simulated by MM5-CALMET model on 28 Sep.2004, provided by Prof. Jimmy Fung of HKUST……………………………………………. 148 Figure I-89: HKO stations and Land-Sea Breeze Effect in HK...... 149 Figure I-90: Wind roses of HKO stations – with topography background (1998-2007, summer day time: 11:00am-16:00pm)...…………………………………………………………….. 150 Figure I-91: Wind roses of HKO stations – with topography background (1998-2007, summer night time: 01:00am-06:00am)……………………………………………………………..... 150 Figure I-92: Topography map of Hong Kong………………………………………………………. 151 Figure I-93: Three observed channeling affecting areas in Hong Kong (including the Kai Tak old airport areas) shown within the red circles…………………………………………….. 152 Figure I-94: Summer wind rose of HKO Sha Tin station…………………………………………… 152 Figure I-95: Summer wind rose of HKO Tuen Mun station………………………………………… 153 Figure I-96: Summer wind rose of HKO Star Ferry (Tsim Sha Tsui) station………………………. 153 Figure I-97: Four main topographical barriers near urban areas and another one on Lantau Island identified……………………………………………………………………………….. 154 Figure I-98: Cool air and outflow analysis map of Berlin Climate Map……………………………. 155 Figure I-99: The cooling effect of the vegetated hillsides of Tuen Mun Areas……………………... 155 Figure I-100: [Left] the profile far left is an understanding of the velocity profile of the katabatic air movement; [right] possible velocities of downhill air movement…………………... 156 Figure I-101: An expert evaluation of the annual wind information by Dr K K Yeung of HKO…...157 Figure I-102: An early and initial expert evaluation of shielding and channeling effects by Professor Lutz Katzschner (2006)……………………………………………………………… 157 Figure I-103: Wind Information Layer－ Prevailing Wind Directions (Summer)…………………. 161 Figure I-104 The structure of the 6 Layers for creating the UC-AnMap (100m x 100m raster based) ……………………………………………………..………………………………… 164 Figure I-105 Work steps for creating the UC-AnMap (Graphics used are indicative)…………….. 164 Figure I-106a Components of Urban Climatic Analysis Map combining Thermal Load Map and Dynamic Potential MapFigure I-106b The UC-AnMap (Classification at Table IB-28), 100 x 100m raster based, without wind information………………………………… 168 Figure I-106b The UC-AnMap (Classification at Table IB-28), 100 x 100m raster based, without wind information………………………………………………………………………….. 169 Figure I-107 The UC-AnMap (Classification at Table IB-28) of Hong Kong with Wind Information Layer - Prevailing Wind Directions (Summer)…….…………………………………171 Figure I-108 Spot measurement in Tsim Sha Tsui and Tsuen Wan….…………………………….174 Figure I-109 The Map of PET Pattern compared with UC-Map for Field Measurement on Tsim Sha Tsui on 19 Sep 2006…………………………………………………………………. 175
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure I-110 The Map of PET data compared with UC-Map for Field Measurement on Tsuen Wan on 15 May 2008 ...... 176 Figure I-111 The relationship between PET and the classes of UC-An Map based on the result of spot field measurement in Tsuen Wan areas on 15 May 2008 ...... 177 Figure I-112 The differences between 2006 version and 2009 version of UC-AnMap ...... 178 Figure I-113 A map of OZP coverage of Hong Kong (as at 4.5.2012)...... 182 Figure I-114 Planning Recommendation Map for Stuttgart ...... 184 Figure I-115 Thermal Environment Map for Tokyo‘s 23 wards and four designated areas………. 187 Figure I-116 The selected dense urban areas of Hong Kong ...... 196 Figure I-117 Building Site Area Ratio of the selected dense urban areas of Hong Kong ...... 196 Figure I-118 Greening, especially tree planting, is encouraged at ground or podium level for better cool the urban environment at the pedestrian level ...... 201 Figure I-119 Global weightings for sub-design criteria ...... 201 Figure I-120 Non-building areas (building set back) to reduce ground coverage is recommended. Greening is encouraged ...... 203 Figure I-121 Ways of creating breezeways and air paths in the urban fabric ...... 204 Figure I-122 Ways of creating breezeways and air paths in the urban fabric ...... 205 Figure I-123 The formualtion of UCPZa for the UC-ReMap ...... 207 Figure I-124 The UC-ReMap, 100m×100m raster based, with wind information - prevailing wind directions (summer) ...... 210 Figure I-125 The UC-ReMap and Hong Kong Planning Framework...... 215 Figure I-126 Four designated areas based on the HK UC-ReMap ...... 216 Figure I-127 Focused areas needing care and attention based on the HK UC-ReMap ...... 220 Figure I-128 Wind Information Layer – Prevailing Wind Directions (Summer) ...... 228 Figure I-129 The Final UC-AnMap of Hong Kong with Wind Information Layer – Prevailing Wind Directions (Summer) ...... 230 Figure I-130 UC-ReMaps of two examples: Stuttgart and (right) Tokyo ...... 231 Figure I-131 The UC-ReMap, 100m×100m raster based, with wind information layer – prevailing wind directions (summer) 236 Figure I-132 UC-Map and Hong Kong Planning Framework ...... 238 Figure II-1 Locations of Hong Kong Observatory weather stations ...... 281 Figure II-2 Mean wind speed (kilometer/hour) of HKO stations 2005 ...... 282 Figure II-3 Wind profiles modified by the building block...... 283 Figure II-4 Ground coverage and wind velocity ratio of 2 areas in Japan ...... 284 Figure II-5 Ground coverage and wind velocity ratio of Mongkok, as compared with other cities in Japan ...... 284 Figure II-6 Streets parallel to the incoming wind ―channels‖ the wind through it effectively ...... 285 Figure II-7 Wind flow patterns and regimes with regular streets and irregular streets ...... 286
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure II-8 Diagrams showing channeling and canyon wind flows ...... 286 Figure II-9 Building dispositions and internal streets can create different patterns of urban morphology even if the streets are ―regular‖ ...... 287 Figure II-11 Flow characteristics over urban forms ...... 289 Figure II-12 Wakes of buildings ...... 289 Figure II-13: Locations of test points at Causeway Bay ...... 313 Figure II-14: Locations of test points at Sheung Wan ...... 314 Figure II-15: Locations of test points at Mong Kok ...... 316 Figure II-16: Locations of test points at Tsim Sha Tsui ...... 318 Figure II-17: Locations of test points at Tsuen Wan ...... 319 Figure II-18: Locations of test points at San Po Kong ...... 321 Figure II-19: Locations of test points at Tuen Mun ...... 323 Figure II-20: Locations of test points at Sha Tin ...... 325 Figure II-21: Locations of test points at Tseung Kwan O ...... 326 Figure II-22: Locations of test points at Wong Chuk Hang ...... 328 Figure III-1 An understanding of urban thermal comfort based on CUHK researches ...... 331 Figure III-2 Cooling effect of air movement ...... 332 Figure III-3 Air Speed offered by the ∆T ...... 332 Figure III-4 A longitudinal study on urban thermal comfort by researchers of CUHK...... 333 Figure III-5 The parameters of the human heat balance ...... 334 Figure III-6 PET vs. wind ...... 336 Figure III-7 Tmrt of HK urban conditions based on summer 2007 non-A/C data of the user survey ...... 340 Figure III-8 The Hong Kong Urban Climatic Analysis Map (2009 version) ...... 342 Figure III-9a Summary of summer VRw ...... 345 Figure III-9b Summary of annual VRw ...... 346 Figure III-10a Summary of summer wind speed(Vp) ...... 347 Figure III-10b Summary of annual wind speed(Vp) ...... 348 Figure III-11 A summary of percentage of test points with median hourly mean wind speed < 1 m/s ...... 352 Figure III-12 Test Area 1-Tsim Sha Tsui ...... 355 Figure III-13 Test Area 2-Mong Kok ...... 356 Figure III-14 Test Area 3-Sheung Wan ...... 357 Figure III-15 Test Area 4-Causeway Bay ...... 358 Figure III-16 Test Area 5-Tsuen Wan ...... 359 Figure III-17 Test Area 6-San Po Kong ...... 360 Figure III-18 Test Area 7-Tuen Mun ...... 361 Figure III-19 Test Area 8-Sha Tin ...... 362
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure III-20 Test Area 9-Tseung Kwan O ...... 363 Figure III-21 Test Area 10-Wong Chuk Hang ...... 364 Figure III-22 News and recent studies on heat-stress-related mortality ...... 366 Figure III-23 Increasing trend of very hot days and very hot nights in Hong Kong from 1890-2000 ...... 366 Figure III-24 Reduction of building ground coverage ...... 372 Figure III-25 Reduction of building ground coverage ...... 372 Figure III-26 Increasing urban permeability ...... 373 Figure III-27 Increasing urban permeability ...... 374 Figure III-28 Increasing urban permeability ...... 374 Figure III-29 Improving urban greenery...... 375 Figure III-30 Improving urban greenery...... 375 Figure III-31 Improving urban greenery...... 376 Figure III-32 Improving urban greenery...... 377 Figure IV-1 Urban Heat Island Effect ...... 468 Figure IV-2 Urban Climatic Planning Recommendation Map of Hong Kong ...... 470 Figure IV-3 Benefits of Tree Planting ...... 473 Figure IV-4 Maximise Greenery in Urban Areas ...... 474 Figure IV-5 Breezeways and Air Paths ...... 475 Figure IV-6 Linkage of Roads, Open Spaces and Low-rise Buildings to Form Breezeways ...... 475 Figure IV-7 Orientation of Street Grids ...... 476 Figure IV-8 Pattern of Street Grids ...... 477 Figure IV-9 Street Widening/Building Setback ...... 477 Figure IV-10 Waterfront Buildings Should Avoid Wind Blockage ...... 478 Figure IV-11 Connecting the Waterfront with Vegetated Hill Backdrops ...... 478 Figure IV-12 Promoting Wind Connectivity ...... 479 Figure IV-13 Varying Height Profile to Promote Air Movements ...... 479 Figure IV-14 Breathing Spaces within the Neighbourhood ...... 480 Figure IV-15 Tall Trees with Wide and Dense Canopy in Plaza ...... 481 Figure IV-16 Encourage Setbacks along Narrow Streets ...... 481 Figure IV-17 Reducing Site Coverage of the Podia to Allow More Open Space at Grade ...... 482 Figure IV-18 Terraced Podium Design ...... 482 Figure IV-19 Building Permeability and Building Separation ...... 483 Figure IV-20 Gaps Between the Podium and Building Blocks to Enhance Air Permeability ...... 483 Figure IV-21 Disposition of Non-building Areas to Create Air Paths ...... 484 Figure IV-22 Building Gaps to Enhance Air Permeability ...... 484 Figure IV-23 Disposition of Towers to Facilitate Downwash ...... 485 Figure IV-24 Projecting Signboards should be Aligned Vertically instead of Horizontally ...... 485
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
Figure IV-25 Stepping Height Profile to Divert Winds to Lower Levels ...... 485 Figure IV-26 Methodology of Formulating Urban Climatic Maps...... 490 Figure IV-27 Urban Climatic Factors for Thermal Load and Dynamic Potential Analysis ...... 491 Figure IV-28 Human Heat Balance Model ...... 491 Figure IV-29 Urban Climatic Analysis Map for Hong Kong ...... 492 Figure IV-30 Wind Information Layer for Hong Kong ...... 494 Figure IV-31 Categorisation of Urban Climatic Classes into Urban Climatic Planning Zones...... 495
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LIST OF TABLES
Table I-1: Typical scale levels for climatic maps ...... 31 Table I-2 Regional factors per grid square (TMG, 2005b) ...... 32 Table I-3 A part table example of hourly mean temperature (July) ...... 67 Table I-4 A part table example of hourly mean temperature (Jan) ...... 68 Table I-5 A part example of users thermal comfort survey result ...... 68 Table I-6 List of HKO weather stations ...... 69 Table I-7 A table of wind speeds and wind directions by hour provided by HKO ...... 71 Table I-8 A part table example of wind speeds and wind directions by month…………………… 72 Table I-9 Meta information and an expert evaluation of HKO station conditions and topographical information ...... 73 Table I-10 Overview of GIS layers for the UC-AnMap ...... 89 Table I-11 T-SVF-Building Volume relation for selected points in the field measurement ...... 94 Table I-12 The Classification of Layer 1 ...... 96 Table I-13 The Classification of Layer 2 ...... 98 Table I-14 The Classification of Layer 3 ...... 101 Table I-15 Estimation of wind velocity...... 105 Table I-16 The Classification of Layer 4 ...... 107 Table I-17 Aerodynamic properties of natural and building surfaces ...... 108 Table I-18 The Classification of Layer 5 ...... 110 Table I-19 The Classification of Layer 6a ...... 113 Table I-20 The Classification of Layer 6b ...... 115 Table I-21 The Classification of Layer 6c ...... 117 Table I-22: Three Wind Conditions and Their Characteristics 129 Table I-25: HKO data coded……………………………………………………………………….. 134 Table I-26: MM5 Data sets………………………………………………………………………… 137 Table I-27: Monthly Prevailing Wind Direction and Mean Wind Speed Recorded at the Observatory and Waglan Island between 1971 and 2000…………………………………………… 144 Table I-28: Wind information and symbols………………………………………………………... 162 Table I-29 An understanding of the characteristics of the 8 classifications ...... 165 Table I-30 Eight Classifications of the UC-AnMap ...... 170 Table I-31 Planning Advices of Stuttgart Planning Recommendation Map ...... 184 Table I-32 Four designated areas ...... 187 Table I-33 Menu of Heat Island Control Measures in the Problem Areas of Tokyo ...... 189 Table I-34 Work Process of the Hong Kong UC-Re-Map ...... 193 Table I-36 Parameters and layers of UC-AnMap ...... 194 Table I-37 UC-AnMap layers and planning parameters ...... 195
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Table I-38 The selected dense urban areas [designated and focused] for the calculation of TBV, BV on BSA, BVD, GC, SGC, BSAR and FAR ...... 197 Table I-39 The relationship between Building Volume Density and Floor Area Ratio ...... 199 Table I-40 The relationship between the planning parameter of Ground Coverage and Site Gound Coverage ...... 203 Table I-41 Suggestions of UC-Map vs. SDC‘s exercise ...... 206 Table I-42 The 5 urban climatic sensitivity zones (UCPZ) of the UC-ReMap ...... 207 Table I-43 General Recommendations for 5 UCPZs ...... 211 Table I-44 Urban Climatic Analytical Characteristics of Four designated areas ...... 216 Table I-45 Descriptions of the layers of the UC-AnMap ...... 226 Table I-46 Descriptions of the 8 urban climatic classes of the UC-AnMap ...... 229 Table I-47 Suggestions of UC-Map vs. SDC‘s exercise ...... 234 Table I-48 The 5 urban climatic planning zones of the UC-ReMap ...... 237 Table II-1a Annual VRw of the test sites ...... 296 Table II-1b Statistical summary of the annual VRw of the test sites ...... 296
Table II-2a Summer VRw of the test sites ...... 297 Table II-2b Statistical summary of the summer VRw of the test sites ...... 297 Table II-3a median wind speed distribution of the test sites for annual case ...... 298 Table II-3b Statistical summary of the median annual wind speed (m/s) of the test sites ...... 298 Table II-4a median wind speed distribution of the test sites for summer case ...... 299 Table II-4b Statistical summary of the median summer wind speed (m/s) of the test sites ...... 299 Table II-5 A generic understanding of connection between the urban morphology and the VR .... 300 Table II-6a Annual VRw of the study areas ...... 304 Table II-6b Statistical summary of the annual VRw of the study areas ...... 304 Table II-7a Summer VRw of the study areas ...... 305 Table II-7b Statistical summary of the summer VRw of the study areas ...... 305 Table II-8a meam wind speed distribution of the study areas for annual case ...... 306 Table II-8b Statistical summary of the median annual wind speed (m/s) of the study areas ...... 306 Table II-9a median wind speed distribution of the study areas for summer case ...... 307 Table II-9b Statistical summary of the median summer wind speed (m/s) of the study areas ...... 307 Table II-10 A generic understanding of connection between the urban morphology and the VR .... 308 Table III-1 An Understanding of Urban Thermal Comfort from AVAs ...... 330 Table III-2 Parameters of thermal comfort ...... 334 Table III-3 Selected thermal comfort indices for indoors and outdoors ...... 335 Table III-4 A tabulation of PET, Ta, Tmrt and v ...... 341 Table III-5 Description of the 8 urban climatic classes of the draft UC-AnMap ...... 343 Table III-6 A parametric understanding of PET based on the HK UC-AnMap ...... 343 Table III-7a A summary of the benchmarking study ...... 350
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Table III-7b A summary of the benchmarking study ...... 351 Table III-8 Summary of the annual median hourly mean wind speeds ...... 353 Table III-9 Summary of summer median hourly mean wind speeds ...... 354 Table III-10 The number of Very hot days can increase from 11 days to 97 days per year with an urban heat island intensity of only 3 degree C...... 367 Table III-11 Impact of urban temperature on energy consumption of Hong Kong ...... 367
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GLOSSARY
Anabatic Wind is one kind of local air current that blows up a hill or mountain slope facing the Sun.
Climatopes are spatial units which exhibit relatively homogenous urban climatic characteristics. For example forest climatopes, water climatopes or urban climatopes. Factors with considerable influence on the urban climate include land use and type, state of vegetation cover, etc.
Dynamic Potential evaluates the ground roughness and therefore the availability of wind and cold air mass exchange of particular localities of urban areas. It mainly depends on the site coverage, availability of natural landscape on slopes, and the proximity to openness.
Environmental Lapse Rate is defined as the rate of negatively change of temperature, with height in the atmosphere.
Katabatic Wind is a high density air flow from a higher elevation mountain down a slope under the force of gravity.
Physiological Equivalent Temperature (PET) is the temperature of a reference environment based on a heat balance model that combines various climatic and physiological variables including air temperature, relative humidity, solar radiation, air movement, clothing and metabolic rate to give a synergetic indication of human thermal comfort.
Radiative Cooling is the atmospheric condition in that an object loses more heat energy by radiation than it gains from its surroundings.
Sky View Factor (SVF) is a measure of the degree to which the sky is obscured by the surroundings for a given point. In urban climatology, it is mainly used to characterise the geometry of urban canyons in urban climatology. Its value is a ratio ranging from zero to one. When obstacles fully block the sky, the factor is zero. When the sky is completely visible, the factor is one.
Thermal Load measures the heat load of particular localities of urban areas and it mainly depends on the building volume (which has an impact on heat storage, and blocking the sky view slowing the city‘s cooling at night), the topography and the availability of green spaces for cooling effect.
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Urban Climatic Analysis Map (UC-AnMap) collates meteorological, planning, land use, topography and vegetation information, based on which, their relationship and effects on winds and thermal comfort are analysed and evaluated spatially.
Urban Climatic Map (UC-Map) is an information and evaluation tool to integrate urban climatic factors and town planning considerations.
Urban Climatic Planning Recommendation Map (UC-ReMap) gives strategic and broad town planning practical guidelines to improve the urban climate and wind environment based on the UC-AnMap and practical constraints.
Wind information gives the background wind speed and direction information at above urban canopy layer (UCL) level. It takes into account surrounding topography. It allows air paths and air mass exchange to be understood.
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ACRONYMS
AVA Air Ventilation Assessment AVAS Air Ventilation Assessment System BD Buildings Department BSA Building Site Area BSAR Building Site Area Ratio BV Building Volume BVD Building Volume Density CASBEE – HI Comprehensive Assessment System for Building Environmental Efficiency- Heat Island CFD-LES Computational Fluid Dynamics – Large Eddy Simulation CFD-RANS Computational Fluid Dynamics –Reynolds-averaged Navier-Stokes CUHK The Chinese University of Hong Kong DP Dynamic Potential DEM Digital Elevation Model EPD Environmental Protection Department FAR Floor Area Ratio GC Ground Coverage GIS Geographical Information System GroundFA Ground Floor Area GIC Government, Institution or Community HKO Hong Kong Observatory H/W Building Height to Street Width Ratio HKUST The Hong Kong University of Science and Technology HKPSG Hong Kong Planning Standards and Guidelines LVp Local Spatial Average Vp LVR Local Spatial Velocity Ratio IR Invitation for Response LAI Leaf Area Index MM5/CALMET Fifth-Generation NCAR/Penn State Mesoscale Model MoE The Ministry of the Environment of the Japan Government NVDI The Normalised Difference Vegetation Index O Open Space OZP Outline Zoning Plan PET Physiological Equivalent Temperature PlanD Planning Department PNAP Practice Notes for Authorized Persons, Registered Structural Engineers and Registered Geotechnical Engineers PNAP APP-151 PNAP APP-151 on ―Building Design to Foster a Quality and Sustainable Built Environment‖ by the Buildings Department PNAP APP-152 PNAP APP-152 on ―Sustainable Building Design Guidelines‖ by the Buildings Department PR Plot Ratio RH Relative Humidity RSL Roughness Sub-Layer SVF Sky View Factor SDC Council for Sustainable Development Ta Air Temperature
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TL Thermal Load TMG Tokyo Metropolitan Government Tmrt Mean Radiant Temperature UBL Urban Wind Boundary Layer UC-AnMap Urban Climatic Analysis Map UC-Map Urban Climatic Map UC-ReMap Urban Climatic Planning Recommendation Map UCL Urban Canopy Layer UCPZ Urban Climatic Planning Zone UHI Urban Heat Island VDI The Association of German Engineers Vp Median Hourly Mean Pedestrian Level Wind Speed Vavg Average Wind Speed VRw Overall Wind Velocity Ratio VRi Directional Wind Velocity Ratio Vs Wind Speed at the Site Wind Availability Level WMO World Meteorological Organization
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INTRODUCTION: THE URBAN CLIMATIC MAP AND STANDARDS FOR WIND ENVIRONMENT - FEASIBILITY STUDY
PROLOGUE
Hong Kong is a high density city situated in the sub-tropical climate region with hot and humid summer months. Owing to our high density urban development, Hong Kong is suffering from the Urban Heat Island (UHI) effect. Our urban areas are significantly warmer than the rural surroundings. As a result of the UHI effect, the number of very hot days (maximum air temperature greater than 33°C) and very hot nights (minimum air temperature greater than 28°C) has increased dramatically. This leads to uncomfortable urban living, heat stress and related health problems, and increase in energy consumption. All in all, this has resulted in poor living quality.
There is a need to optimise the planning and design of our city to facilitate more wind penetration through the city fabric, and to attain a higher quality urban living environment with thermal relief and reduction of heat stress, especially in the public realm.
1.1 BACKGROUND
Based on the “Feasibility Study for Establishment of Air Ventilation Assessment (AVA) System” (AVAS Study) completed by the Planning Department in November 2005, a set of planning guidelines for promoting better air ventilation was added in Chapter 11 (i.e. Urban Design Guidelines) of the Hong Kong Planning Standards and Guidelines (HKPSG) and promulgated in August 2006. In tandem, the then Housing, Planning and Lands Bureau and Environment, Transport and Works Bureau jointly issued a Technical Circular No. 1/06 on Air Ventilation Assessments, setting out a framework for AVA and requiring all major government projects to include AVA as one of the planning and design considerations. As there is no benchmark, the AVA System adopts an “option-comparison-and-improvement” approach. The AVAS Study suggested that apart from considering the urban air ventilation environment, a more holistic approach to reviewing Hong Kong’s urban climatic conditions for better planning decision making at the territorial and district levels should be targeted.
In July 2006, the Planning Department commissioned the consultancy on the “Urban Climatic Map and Standards for Wind Environment – Feasibility Study” (the Study) to comprehensively and scientifically assess the urban climatic characteristics of different parts of Hong Kong and to formulate holistic planning and design measures to achieve long-term improvement of the urban living environment.
1.2 STUDY OBJECTIVES
The Study provides a more scientific and objective basis for identifying climatically valuable and sensitive areas and assessing the urban climatic and air ventilation impacts of major development and planning proposals.
This Study has four main tasks, namely “Formulation of Urban Climatic Maps of Hong Kong”; “Wind Tunnel Benchmarking Studies”; “Establishment of a Wind
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Performance Criterion”; and “Refinement of the AVA System”.
1.3 STRUCTURE OF THE REPORT
For easy reading and reference, the Final Report is divided into 4 parts. Each part is dedicated to one of the four major tasks listed above. The four parts are as follows:
PART I: Urban Climatic Map;
PART II: Wind Tunnel Benchmarking Studies;
PART III: Establishment of Wind Performance Criterion; and
PART IV: Refinement of the AVA System.
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PART I: URBAN CLIMATIC MAP (UC-MAP)
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PART I(A): URBAN CLIMATIC MAP (UC-MAP)
PART I(A)-1 INTRODUCTION
There is a general understanding that ―A different climate is produced by the built environment in urban areas – the urban climate.‖ Today, the term "urban climate" also encompasses the change in the natural composition of the air through anthropological influences (air pollution and aerosols). Every structure has an influence upon the individual climatic elements. Large built-up areas divorce themselves in a climatic sense from their surrounding landscape. The significant causes contributing to the production of a separate urban climate lie in the far-reaching alteration of the heat budget and the local wind field. The character of a typical urban climate is first and foremost dependent upon the size of the city, but is also influenced by the topography, urban form, and the proportion of open space. Although there are elements of the urban climate that differentiate themselves very little based on the location in the city (such as sunlight and precipitation), other climatic elements – affected by the heat retention capacities of buildings, by the soil capping, by altered water budgets, and by heat discharges – show substantial spatial variation (such as temperature and wind patterns). Small spatial variations can be found in areas of buildings, streets, and green spaces.‖ [See ―Climate Booklet for Urban Development‖1]
There is a vision to design a city that is sustainable, healthy, comfortable, and a place that its inhabitants could enjoy. To achieve this, it is necessary to factor the urban climatic considerations holistically and strategically into the planning process. UC-Map is considered an important information tool (Scherer et al., 1999) to present urban climate information relevant for planning, so that planners could easily make reference to during the planning and design process.
UC-Map is an information and evaluation tool to integrate urban climatic factors and town planning considerations to assist planning decision. UC-Map typically has two main components. The Urban Climatic Analysis Map (UC-AnMap) collates meteorological, planning, land use, topography and vegetation information, based on which, their relationship and effects on winds and thermal comfort are analysed and evaluated spatially. Secondly, the Urban Climatic Planning Recommendation Map (UC-ReMap) gives strategic and broad
1 ―Climate Booklet for Urban Development, Reference for Zoning and Planning‖, by the Office for Environmental Protection, City of Stuttgart. (http://www.staedtebauliche-klimafibel.de/Climate_Booklet/index- 1.htm)
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This report firstly explains the concept of UC-Map and outlines a general understanding of the UC-AnMap through desktop studies on international examples of urban climatic mapping in Part I(A). Secondly, in Part I(B), following the state-of-the-art knowledge of UC-AnMap guidelines, the scientific basis of the methodology of UC-AnMap for Hong Kong is developed and explained from Thermal Load and Dynamic Potential aspects based on Hong Kong‘s unique urban morphology. Finally, based on expert evaluation and synergising the urban climatic factors and urban planning parameters, the UC-ReMap for Hong Kong would be presented in Part I(C).
1.1 DEFINITION OF UC-MAP
UC-Map consists of two individual components, i.e. UC-AnMap and UC-ReMap. Their differences are that the former map is climate-oriented while the latter map is planning- oriented.
The UC-AnMap presents a classification system of different climatopes 2 , based on the climatic characteristics of Dynamic Potential3 and Thermal Load4; it also contains wind, air path and air mass exchange information. An UC-AnMap of a city displays the spatial characteristics and classification of climatopes representing areas of distinct local climates. Based on available information collated, the map takes into account a balanced expert evaluation of positive and negative effects of the local climate, topography, vegetation, urban morphology, and wind patterns.
Based on the analysis obtained from the UC-AnMap, a UC-ReMap can be created to show the corresponding planning recommendations together with their rationales. The UC-AnMap
2 Climatopes are spatial units which exhibit relatively homogenous urban climatic characteristics. For example forest climatopes, water climatopes or urban climatopes. Factors with considerable influence on the urban climate include land use and type, state of vegetation cover, etc.
3 Dynamic Potential evaluates the ground roughness and therefore the availability of wind and cool air mass exchange of particular localities of urban areas. It mainly depends on the site coverage, availability of natural landscape on slopes, and the proximity to openness.
4 Thermal Load measures the heat load of particular localities of urban areas and it mainly depends on the building volume (which has an impact on heat storage, and blocking the sky view, thus slowing the city‘s cooling at night), the topography and the availability of green spaces for cooling effect.
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The UC-ReMap is an understanding of the UC-AnMap based on planning considerations which results in guidelines that planners can make reference to. Based on the analysis obtained from the UC-AnMap, similar climatopes are grouped into climatic planning zones. The UC-ReMap can be developed to include the corresponding planning recommendations and guidelines of each zone with the aim of mitigating the current negative situation and protecting the positive situation. These zones are represented in different colours and symbols to illustrate their respective recommended actions. Urban climatologist and planners must work closely together to ensure that the climatic knowledge and evaluations of the UC- AnMap are accurately translated into appropriate planning recommendations under the UC- ReMap.
1.2 STATE-OF-THE-ART OF UC-MAP
Since the 1980s, researchers in the field of urban climatology from Europe, North America, Asia and South America have tried to develop the idea of urban climate assessment and analysis (Figure I-1)(See Part I-Appendix 1). Among them, Germany is a leading country in conducting urban climate analysis. After the re-unification of Germany, several cities in the former German Democratic Republic were analysed in terms of urban climate and synthetic climate function maps were constructed.
By introducing the concept of UC-Map, key urban climatic factors including meteorological data for climate assessment are mapped on to the base map of land use, topography and urban geometry. This UC-Map makes available the necessary climatic information to planners in a comprehendible manner, which otherwise, would only be legible to scientists and climate experts.
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Figure I-1 UC-Map around the world
In Germany, there is a strong emphasis on urban climate research that also includes human- biometeorology. This is partly because of the legal requirement that climate issues have to be considered in regional and urban planning projects. Guidelines VDI 3787 (Part 1), regarding the urban climate mapping details, was published by the Association of German Engineers (VDI) in 1997. The Guideline contains expert recommendations on methods and symbols to be used for drawing up the UC-Maps.
Based on the VDI guideline, UC-AnMap characterises a balanced consideration of the heat exchange – including Dynamic Potential, the trans-evaporation, topographical, and the Thermal Load. It further takes into account Wind Information5 in local weather conditions within the Urban Canopy Level6 (UCL) layer. The process of making UC-AnMap is one of expert evaluations based on the spatially mapped information of various factors. The key is to have a synergetic approach that takes a balanced consideration of the conditions of all the factors in an order to provide interpretation in planning terms. Scientific and mathematical precision is typically either not possible or not necessary for the scale of operation in the planning process. Based on the UC-AnMap, UC-ReMap could be formulated to establish the in-principle suitability for an intended development from the urban climatic point of view.
5 Wind Information gives the wind speed and direction information of prevailing winds at above urban canopy layer level. It takes into account surrounding topography. It allows air paths and air mass exchange to be understood. For this study, MM5 simulated wind information data, summer and annual, will be collated, evaluated and considered.
6 Urban Canopy Layer is the layer between the ground surface and the roof of buildings in the urban region.
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Besides Germany, the idea of UC-Map has also been developed and adopted by many countries and researchers around the world. (PART I-Appendix 1 summaries the relevant UC-Map studies in Sweden, Switzerland, Norway, Greece, Poland, Brazil, Japan and Thailand.) Among them, Germany and Japan are the two focused countries for desktop research in this study.
1.3 MODUS OPERANDI OF UC-MAP
The study provides objective urban climatic information which is useful and relevant to town planning in Hong Kong in considering:
. Land Use . Layout . Development Bulk . Building Disposition . Open Spaces . Greeneries and Landscaping
Two urban climatic factors: Wind and Thermal Load, are important for town planning and urban design in Hong Kong. They will be the focus of the study particularly in relation to the Thermal Comfort of the built environment.
The UC-Map usually consists of a series of individual maps (layers), which take into account various climatic factors and geographical factors influencing urban climate. These factors could be about solar radiation, air temperature, humidity, land use, wind, etc. Typical scales for maps on climate-dependent planning are presented in the following Table I-1. For regional analysis and master plan for a city (a scale from 1:50,000 to 1:100,000) and district planning (1:5,000 to 1:7,500), UC-Map is considered a suitable tool to provide urban climatic guidelines for town planning. Detailed microclimatic analysis may sometimes be needed at a scale smaller than 1:500 at estate or building design levels.
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Table I-1: Typical scale levels for climatic maps
Scale Planning Level Tool
master plan; 1:50,000 to 1:100,000 UC-Map regional planning
1:5,000 to 1:7,500 district planning UC-Map
estate or 1:500 & smaller microclimatic analysis building design
UC-Map emphasises more on district-level guidelines than site-specific guidelines. The creation of UC-Map should be coherent with the actual planning strategies. From the perspective of district planning, Outline Zoning Plan (OZP) is the primary land use planning framework in Hong Kong. The OZP is a statutory plan at the district level. Figure I-2 shows all the current OZP scheme areas in Hong Kong. OZPs are typically prepared at a scale of 1:5,000 to 1:7,500.
Based on the desktop research, and making reference to the professional planning process of Hong Kong. It is determined that the most suitable UC-Map scale of operation for Hong Kong is at a scale of 1:5,000 and the UC-Map will be reported at 100m x 100m grid. With this resolution, the order of climatope patterns and Thermal Load and Dynamic Potential of the urban morphology is at a scale suitable and necessary for district planning purposes.
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Figure I-2 A map of OZP coverage of Hong Kong (as at 4.5.2012)
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PART I(A)-2 DESKTOP STUDIES
2.1 OVERVIEW
Planning strategies and policies must be tailored to suit different climatic, cultural, economic and urban contexts. The merit of a desktop study of international experiences mainly lies in obtaining an understanding of UC-Mapping issues that could be usefully adapted to the context of Hong Kong.
Pioneering work in the following selected cities, Stuttgart and Kassel in Germany and Tokyo in Japan. (Figure I-3), are useful references to understanding the basis, framework and application of UC-Map.
Figure I-3 Desktop studies on selected international cities
The concept of UC-Map started in Germany in the early 1980s when there was intense public opinion and political will to plan for the future in a responsible and sensitive moment, with respect to the natural environment. In Germany, the law explicitly states that no new development should adversely affect the natural environment. Within this context, planners, meteorologists and scientists in Germany started to draft UC-Maps, and have attempted to synergise climatic, topographical and urban planning parameters in order to objectively guide the planning decision making process.
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An early Air Path Map (being a basis of the UC-AnMap) of Munich is shown below (Figure I-4). The Air Path Map was an attempt to understand the urban air ventilation routes of the city so that no new developments would obstruct these paths which could transfer the fresh cool air into the central urban areas. A summary of the studies of UC-Map for other countries is presented in PART I-Appendix 1.
Figure I-4 Air path analysis map for Munich, Germany (Matzarakis & Mayer, 2008)
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2.2 CASE STUDY I – STUTTGART, GERMANY
2.2.1 Background and Context
2.2.1.1 City Description
Geography: Located in southern Germany; Total area is 207 km2 ; Urbanised area is 49% (102 km2 ); Forest area is 25%;
Population: Total population is about 590,000; Population density is 2,850 /km2
Topography: Lowest point is 207m above sea level; highest point is 549m above sea level
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2.2.1.2 Basic Climatic Conditions
Stuttgart‘s climate is mild with an average annual temperature of about 10 o C at the centre of the city and about 8.4 o C in the more elevated outskirts (City of Stuttgart, Office for Environmental Protection, 2006).
In general, wind blows only lightly in Stuttgart, because the city centre is located in the basin and surrounded by four surrounding mountainous regions (Black Forest, Swabian Alb, Schurwald and Swabian-Franconian Forest) (Figure I-5). The light wind conditions are further intensified by the small air pressure differences common to the southwest of Germany. The average wind speed per year is about 1.5 m/s in the city centre and about 2.5 m/s in the higher regions. This light wind condition and topographical characteristics raise the issue of insufficient natural air ventilation and also heat island effects, especially in the city centre.
Figure I-5 City of Stuttgart
2.2.1.3 Expanding of Stuttgart’s Settlement Areas
Stuttgart has developed from a rural settlement (occupying 6% of the total area) with a population of 270,000 in 1900, to a highly-urbanised city (occupying about 50% of the area) with a population of 586,000 in 2000. Although the population has not increased much in the past 100 years, the built-up areas including commercial and residential developments within the city have expanded 9 times than that of 100 years ago (Figure I-6).
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Figure I-6 Development of Stuttgart in the last 100 years (Baumüller, 2006)
Therefore, the increase of urbanised area brings with it urban climatic concerns, such as UHI effect. The intensification of urbanisation process also brings with it transportation and thus air pollution issues.
2.2.1.4 Climate as a Public Interest in Planning and Zoning
It has been recognised in Germany that intensive land uses put burden on the environment. The government considers adopting cautious planning approach and using co-ordinated regional and urban development planning as a means for environmental protection. This emphasis is also enshrined in the German Constitution, which defines environmental protection as a state goal under Article 20a.
According to Chapter 1(5) of the German Federal Building Law (Figure I-7), urban development planning has to be sustainable, and must cater for social, economic and ecological needs. Urban development plans have to contribute to an environment fit for human beings by balancing the protection and use of natural resources. They also have to develop the townscape and landscape with responsibility for future generations. A site control plan that has been developed in accordance with the land use plan of a municipality has binding authority to determine whether land areas are used in a manner that the environment could justifiably accommodate.
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Figure I-7 German Federal Building Law
2.2.1.5 Rise of a Need for Information-Based Maps
In order to impose proper control on new residential and commercial development, fundamental studies of urban climate and air ventilation are gaining increasing importance in land use planning in densely – urbanised areas.
Since planning controls refer to specific areas, the use of maps as an information base is recommended. Maps are, therefore, very useful tools for planners, and are also a convenient means of communicating information to politicians and the public. These maps are expected to contain spatially – related cartographic data, with well-defined climatic and air ventilation goals. Furthermore, with the assistance of climatic maps, important questions concerning climatic aspects in urban planning could be answered, in terms of:
- Reduction of UHI effect - Reduction of air pollution - Ventilation for better urban climate - Ventilation for better air quality - Minimising shadowing on buildings
2.2.2 Methodology
2.2.2.1 Responsible Researchers
A research team (shown in Figure I-8) led by Prof. Dr. J. Baumüller in the Office of Environmental Protection for the Department for Urban Climatology, in Stuttgart is responsible for maps on urban climate, air pollution, and noise abatement planning.
This Department of Urban Climatology has been established in the municipality of Stuttgart since the year 1938. Methodology on urban climate analysis has therefore been well developed for the city.
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Figure I-8 The Team of the Department of Urban Climatology in Stuttgart
2.2.2.2 Collection of Basic Data
The production of such climatic and air ventilation maps requires the collection of technical measurements for individual parameters, with map – scale representation as well as simulations with statistical regression models (Gerth, 1986) or macro-scale models (Fiedler, 1991).
The collection of basic data includes two infrared aerial images taken of the entire study area. In addition, for a period of one year, the German Weather Service carried out an extensive field measurment programme (of temperature, humidity, and wind) and produced cartographic representations of various climatic elements from the collected data. All together, the important bases for producing climatic and air ventilation maps include the following information:
- Topographic Maps - City Maps - Land Use Plans - Aerial Photographs - Infrared Aerial Images (An example is in Figure I-9, which shows a thermal map of the Stuttgart city area in the evening situation)
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- Meteorological base data (An example is in Figure I-10, which shows average daily wind velocity in Stuttgart city area) - Air ventilation information
Figure IThese-9 Thermal basic map maps of the are Stuttgart incorporated city area into in a CD ―UrbanFigure ClimateI-10 Average 21‖ (dailyFigure wind IA -velocity11), in whichthe evening includes situation basic materials (averaged) for urban climate and for the planning,Stuttgart prepared city area by (Source: Nachbarschaftsverband Stuttgart, 1992). (Source: Nachbarschaftsverband Stuttgart, 1992). The Office of Environmental Protection within Department of Urban Climatology of the Stuttgart city is responsible for compiling the information, which is based on the ISY-Raum system (a computer-based system) to present data, perform calculations and visualise results as a planning instrument for answering urban climatic questions arising in the context of the Stuttgart 21 Project. The CD is available for public use.
Figure I-11 CD-ROM “City climate 21”
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2.2.2.3 Production of Urban Climatic Analysis Map
The study results, including the above information maps for each individual climatic elements, are summarised and depicted in analysis maps of 1: 20,000 scale, which corresponds to that of land-use plans. The methodology to derive a UC-AnMap is mainly a classification and summary of climatopes and cold air collection areas. The symbols used in the maps correspond largely to the VDI 3787, Section 1.
Since the microclimatic characteristics of built-up areas are determined basically by the land use and the type of development, the climatopes are named after the dominant land-use type or building use. These climatopes include water climatope, open land climatope, forest climatope, greenbelt climatope, city climatope, commercial climatope, industry climatope and the others.
The Climate Atlas (Figure I-12) produced by the Stuttgart Regional Federation for the territory of the federation and the bordering parts of the Middle Neckar Region show how the concerns of climate and air ventilation can be incorporated into cartographic representations for land-use planning (Baumüller et al., 1992a). Figure I-13 is one example of the climate analysis maps depicting the local-climatic conditions in this region as a cartographic overview.
Figure I-12 Climate Atlas produced by the Stuttgart Regional Federation for the territory of the federation and the bordering parts of the Middle Neckar Region (Nachbarschaftsverband Stuttgart, 1992).
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Figure I-13 Example of a climate analysis map for Stuttgart city areas
2.2.2.4 (NachbarschaftsverbandProduction of Maps Stuttgart,with Recommendations for Planning 1992). Following the UC-AnMap, an UC-ReMap with recommendations for planning actions (shown in Figure I-14) is produced. This map contains an integrated assessment of the materials presented in the analysis map alongside spatial planning considerations. The symbols denote the sensitivity of the subjectland areas against changes in land use, from which climatically-based conditions and measures can be recommended for planning and zoning purposes.
The first and foremost goal of the planning recommendations, as considered by German researchers, is to enable the planners to give more weight to climatic considerations and criteria (Beckröge, 1990). As such, a planning project should incorporate the guidelines of the ―Planning Recommendations‖ map. It is also suggested that planners and politicians must objectively weigh urban climatic compatibility against other planning considerations. To avoid negative climatic effects as far as possible, detailed appraisals and assessments in planning are usually necessary.
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Both UC-AnMap and UC-ReMap are not specific to the level of individual land parcels. Tolerances can be up to 100m.
Figure I-14 Example map with recommendations for planning for Stuttgart city areas (Baumüller et al., 1992a)
2.2.3 Implementation
With the assistance of UC-AnMap and UC-ReMap, researchers suggest the following climatically-responsive planning objectives that can be targeted when the planning actions are undertaken:
- Improving living conditions in terms of climatic comfort - Improving on ventilation of developments - Supporting fresh air provision through local wind systems - Reducing the release of air pollutants and greenhouse gases - Properly evaluating current or expected pollution levels - Properly reacting to polluting situations by adjusting land uses
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Furthermore, since the basic improvement measure for the urban climate is the provision of green spaces and vegetation in the built-up areas of the city, the focus of climatically- responsive urban planning would primarily be on the preservation and reprovision of natural vegetation.
To complement the plan, all planning relevant climatic studies have been incoporated into a ―Climate Booklet for Urban Development – References for Zoning and Planning‖ (Figure I- 15), released both in print and available on the Internet by the Office for Environmental Protection of Stuttgart, under the Ministry of Economy of the Federal State. Selected topics and concrete planning recommendations are the highlights of the booklet, in which the planning, technical, and legal possibilities and limitations for climatically-responsive urban development are explained. The Ministry of Economy hopes to assist all those concerned with urban development and planning to gain further knowledge of the urban climate.
Figure I-15 Climate Booklet for Urban Development, Reference for Zoning and Planning, by the Office for Environmental Protection, City of Stuttgart
2.2.4 Lessons for Hong Kong
The Office for Urban Climatology in Stuttgart was established more than 70 years ago and has been responsible for urban climate studies for the city ever since. It is demonstrated that planners have to collaborate closely with urban climatologists over a long period of time in order to collect and acquire climatic information useful for building up an urban climatic understanding. Field measurement data and the urban canopy level data are particularly important. However, such data are generally unavailable from observatories.
The public should be consulted at various stages of the planning process. Furthermore, more comprehensive urban climatic studies can contribute to sustainable development. There is also a call for coordinated planning effort in tackling environmental issues, including air quality, noise, and air ventilation.
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2.3 CASE STUDY II – KASSEL, GERMANY
2.3.1 Background and Context
2.3.1.1 City Description
Geography: Located in central Germany; Total area of 106.77 km2 ;
Population: Total population is 194,176; Population density is 1,819 /km2
Topography: Situated in a valley surrounded by mountains with a height difference of 500m (lowest point is 133 m above sea level; highest point is 615 m above sea level) within a range of 10 km
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2.3.1.2 Basic Climatic Conditions
The monthly average temperature for Kassel is lowest in January (about -0.2ºC ) and highest in July (about 21.9ºC ), as measured from a weather station at the elevation of 233 m (Figure I-16). Due to topographical characteristic, which is surrounded by relatively high mountains (Figure I-17), the UHI intensity of Kassel is about 2ºC. Surrounding mountains lead to strong thermal-induced ventilation system across the city. However, the wind condition within the city area is still weak with a mean wind speed below 2 m/s.
Buildings
Monthly average of max
daily temperature Monthly average of min daily temperature
Figure I-16 Monthly average of the minimum and maximum daily temperatures (o C) for Kassel, Germany
Figure I-17 Pictures for City of Kassel, Germany
2.3.1.3 Pursuing the Goal of “Ideal Urban Climate” The city of Kassel is subject to German Federal Building Law, same as the city of Stuttgart. As such, climatic issues have to be taken into consideration in urban planning. In the context of existing climatic conditions and problems in Kassel, Professor Lutz Katzschner of the University of Kassel proposed that the definition of ―ideal urban climate‖ should be a goal for
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In early 1980‘s, when the city expansion plan for Kassel was under review, the local government was aware of the adverse effects of Kassel‘s geographical location within a valley. The public‘s awareness of the problems of air pollution and thermal comfort have been raised since. The city government thus started to consider environmental effects of new plans and buildings before their actual construction. Subsequently, the Regional Planning Board of Kassel decided to include clearer information of urban climatic evaluation in regional planning and master planning. Under these circumstances, the first version of urban climatic map was produced by Professor Lutz Katzschner in 1990 to address the problem of thermal comfort. It was then updated in 2003, especially with new information on land use. Within the 13 year interval, the extent of greenery and industry areas have been largely modified. GIS is used as the main tool to produce the second version of this urban climatic map.
2.3.2 Methodology
2.3.2.1 Purpose
UC-Maps were created as a tool to evaluate the human – biometerological conditions, because these maps could cover the detailed information of the urban climate pattern including heat island effects and ventilation. The bioclimatic conditions were then expressed using the thermal index of the Physiological Equivalent Temperature (PET), based on the heat balance model (Höppe, 1993, 1999).
2.3.2.2 Process
The UC-AnMap was created by Professor Lutz Katzschner by classifying urban climatic conditions into an 8-class system. The main determining parameters for thermal comfort were the mean radiation temperature and wind velocity. The following figures (Figure I-18) show the major study framework and steps.
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investigation and evaluation of the existing data 1
classification of the classification of topographical classification of structures situation land use for dynamics slope and air path for thermal aspects classification
air pollution 2
measure- measure- ments ments
dynamic analysis thermal anaysis 3
urban climate map drawings of qualities and processes 4
analysis of problem areas 5 evaluation of climatic processes with different classifications
urban climate advice map with planning advices following climatic judgements 6
Figure I-18 Structures and methods for thermal comfort zoning
2.3.2.3 Urban Climatic Map
Figure IA-19 First version of UC-AnMap of Kassel Created in 1990 by Professor Lutz Katzschner
This UC-AnMap was derived based on a theoretical approach of calculating the thermal load and dynamic potential pattern using data on land use, topography, vegetation percentages, effective building heights, and roughness length (Figure I-19). These parameters were combined and calculated by a GIS program on urban climatic characteristics. (See Figure I-
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20). All processing data are in the resolution of 10m x 10m. An UC-ReMap could then be produced with eight planning classifications (Figure I-21).
Figure I-20 GIS calculations and classifications for UC-AnMap
Figure I-21 Land use map [left], thermal condition map [middle], UC-ReMap [right]
A detailed analysis map in the district of southwest Kassel was also developed (Figure I-22). After the thermal and dynamic based climatic map was developed, the meteorological data were then further inputed to calculate the PET value. Figure I-23 demonstrates a more in- depth investigation carried out with measurements and calculations of the thermal index PET.
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Figure I-22 UC-AnMap for Kassel city [left] and for Southwest Kassel [right]
Figure I-23 UC-Map of the investigation area in a scale of 1: 5,000 (Katzschner, 2005)
2.3.2.4 Planning Recommendation Map
Based on 8 classifications in the above UC-AnMap, an UC-ReMap was developed to provide planning guidelines for each classification zone. (See Figure I-24). Within each zone, special planning guidelines were provided to ensure that the urban climatic situation within that zone will not be worsened, and possibily even improved.
Based on the strategic understanding of the UC-ReMap, planners could more objectively and scientifically prepare the master plan of the city with strategies towards attaining the desired
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Figure I-24 UC-ReMap for Kassel (Katzschner, 2005)
2.3.3 Implementation
The UC-ReMap serves as a piece of basic information to guide all development projects. For each project, theUC-ReMap should be referred to and applied throughout the whole development process. More importantly, planners have to demonstrate how they have considered urban climatic issues.
Once the UC-ReMap was created, it was incorporated into master plan prepared by the Regional Planning Board of Kassel. According to the UC-ReMap, critical areas in terms of urban climate are identified for zoomed-in investigation. When these critical areas are subject to development, each project would undergo a detailed climatic study. Based on such studies, a detailed climatic map of larger scale of 1:2,000 for that particular area was then created by certificated consultants. This larger-scale climatic map finally goes back to the Regional Planning Board for the ultimate decision making.
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2.3.4 Lessons for Hong Kong
In the case of Kassel, implementation of the UC-ReMap recommendations is mainly through prescriptive means. The UC-Map is incorporated into a master plan of a scale of 1:5,000, which is not a performance-based guide. The UC-ReMap clearly specifies rigid restrictions on building coverage (together with building orientation), percentage of greenery, gaps between buildings and building height.
Regarding metrological data collection, more long-term data (i.e. solar radiation, wind, temperature, etc.) along with the vertical wind profile within urban canopy level are needed for a comprehensive understanding of distribution of urban climatic parameters. The interactions between regional climate and urban structures should be better understood; hence, a comprehensive long-term monitoring programme with data collection is essential, both to obtain additional information, and to monitor progresses and results.
Since the UC-Map is used together with the master plan, its review should coincide with the regular updating of master plan. The review process in Kassel is every 6 years (every 10 years in the past).
The UC-Map for Kassel has 8 classifications for the city region. But in Hong Kong, the classifications should fit in with its more topographical characteristics. It should be noted that Kassel has just one dominant topography, i.e. valley. The wind environment is thus more homogeneously distributed among the city region.
Close cooperation among GIS experts and town planners in the Planning Department is also anticipated for better data integration.
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2.4 CASE STUDY III – TOKYO, JAPAN
2.4.1 Background and Context
2.4.1.1 City Description
Districts: As an administrative region of Japan, it consists of 23 central ―special wards‖ and many suburban cities.
Geography: Near the center of Japan, occupying 2,187 km2 in area.
Population: Total population is 13 million, which is about 10% of the total population of Japan; Population density is 5,796 / km2.
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2.4.1.2 Basic Climatic Conditions
Tokyo has a generally warm and humid climate (please refer to Figure I-25 & Figure I-26). Its yearly average temperature is 16 o C, with August being the hottest and January the coldest. There is a temperate difference of about 20 o C between summer and winter. Excessive heat in the summer months is more of a problem than severe coldness in the winter; the situation is becoming more severe in recent years. In particular, in the summer of 2004, temperature hit record high at 42.7 o C in the centre of Tokyo. Temperatures of over 30 oC had continued for more than one month. This was partly due to global warming, but it is also caused by the UHI effect, which is a common phenomenon in high density cities, with Tokyo being one of them (Figure I-27).
Figure I-25 Normal temperatures in Figure I-26 Normal rainfall and relative Tokyo humidity in Tokyo
Figure I-27 The high-density, high-rise urban development in Tokyo
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2.4.1.3 Recognition of UHI as a Key Environmental Issue
Tokyo is one of the cities in the world where energy is consumed on a massive scale. By mitigating the UHI effect, this will not only be beneficial to the city itself, but would also enable Tokyo to play a more important role in combating global warming.
With a recognised rising trend in energy consumption and excessive urban heats (with increasingly intensified ―twin warmings‖, i.e. UHI phenomenon and global warming) every year, the Tokyo Metropolitan Government (TMG) has implemented a policy named ‗Tokyo Challenge‘, to combat the ―twin warmings‖ since 2002.
by Urban and Global Environmental Planning Section, Bureau of the Environment, Tokyo Metropolitan Government
2.4.1.4 Impact of UHI effect
Tokyo and five other Japanese cities have seen average temperature rises of 2 – 3oC, much higher than the global average of 0.6oC. As such, it could be said that the UHI effect is more pronounced in Tokyo than the effects of global warming.
2.4.1.5 Causes of the UHI effect
Regarding the causes of the UHI effect, four main factors are identified. i) Increased anthropogenic heat release: Heat release resulting from energy consumptions in urban areas ii) Changes in surface cover: Reduced surface evapotranspiration capacity due to fewer green areas; The heat storage effect of man-made construction materials such as concrete and asphalt iii) Urban structure: Heat stagnation due to densely packed buildings; Expansion of urban areas iv) Others: The greenhouse effects of fine-particulate air pollution in the urban atmosphere
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2.4.1.6 Mitigation Measures to UHI
Many sporadic measures to mitigate the UHI effect have been put into practice. They include: . rooftop greening . exterior wall greening . water-retentive pavement . thermo-shield pavement
As one of the proactive mitigation measures, the ‗Comprehensive Assessment System for Building Environmental Efficiency- Heat Island‘ (CASBEE – HI) system was developed in 2005 as a tool for evaluating the effectiveness of these mitigation measures and to assess the overall environmental performance of buildings. (See Figure I-28). .
Figure I-28 CASBEE for new construction and CASBEE – HI in Japan (IBEC, 2006)
Moreover, where the above measures were found to be ineffective in combating the UHI effect, regional mitigation measures are recommended in the early process of urban planning to be implemented at the same time in order to produce satisfactory results. Intensive environmental investigations should be carried out before urban redevelopment and renewal.
In this context, a ―Thermal Environment Map‖ was produced for Tokyo, as one of the approaches adopted by the government in combating the UHI effect.
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2.4.2 Methodology
2.4.2.1 Thermal Environment Map
The Tokyo Metropolitan Government produced a ―Thermal Environment Map‖ in April 2005.
Figure I-29 Thermal Environment Map for Tokyo (TMG, 2005b)
This Thermal Environment Map, with a resolution of 500m x 500m, (Figure I-29) shows the atmospheric impact (Thermal Load) of anthropogenic heat release and surface cover conditions in Tokyo‘s central 23 wards.
2.4.2.2 Area Classifications
Legends and explanations for the Tokyo Thermal Environment Map is illustrated in Figure IA-30. In particular, Type I (high – density commercial areas) and Type II (high – density residential areas), whose atmospheric impacts are relatively large, are classified and designated by different colours according to their Thermal Load.
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Figure I-30 Legends and Explanations for Thermal Environment Map (TMG, 2005b)
Altogether, there are 17 regional factors in Table I-2 identified for the UHI phenomenon. They are grouped into 5 classifications based on their thermal environmental characteristics and plotted and color-coded on the map, according to their relative size of loading on the atmosphere.
Table I-2 Regional factors per grid square (TMG, 2005b) Categories Item Heat radiated from buildings Heat radiated from district cooling Heat radiated from automobiles Anthropogenic Heat Heat radiated from railways Heat radiated from businesses Anthropogenic heat (sensible heat) Anthropogenic heat (latent heat)
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Water-area ratio Bare land and grassland-area ratio
Ground Surface Covering Vegetation-area ratio Asphalt-area ratio
Buildings-area ratio
Average building width Average building height Shape of Building Sky view factor
Proportion of office floor space Building Use Proportion of residential floor space
2.4.3 Implementation
The Thermal Environment Map enables the planning decision makers to appreciate the regional distribution of factors contributing to the UHI phenomenon, and also the magnitude of their thermal loading on the atmosphere.
2.4.3.1 Four Designated Areas where special attention is needed
Based on this map, the Tokyo Metropolitan Government has designated four areas as ―areas for the implementation of UHI effect mitigation measures‖ (Figure IA-29). Within them, Central Tokyo Area and Shinjuku Area are business cluster areas; Osaki & Meguro Area is a high-density residential area; Areas surrounding Shinagawa Station is a future development area.
These four Designated Areas were selected based on the following criteria: relatively large thermal loading according to the Thermal Environment Map Priority areas for redevelopment with the potential to attract environmentally friendly development by the private sector areas where a wide range of development can be expected and where adequate planning control should be systematically introduced
Efforts are now underway to implement mitigation measures designed to suit the characteristics of each area.
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2.4.3.2 “Guidelines for UHI Mitigation Measures”
Furthermore, in July 2005, the Tokyo Metropolitan Government developed the ―Guidelines for UHI Mitigation Measures‖ to encourage private businesses and the Tokyo public to implement mitigation measures according to the thermal environment in which they operate or live in (TMG, 2005a). These guidelines comprise: i) the Thermal Environment Map ii) a set of area-specific mitigation measures iii) a set of building-specific mitigation measures
With the designated areas adopted as model areas by the central government, the Tokyo Metropolitan Government then established the ―UHI Mitigation Measures Designated Areas Council‖ to undertake concerted efforts to implement the program. This involves collaboration with the central government and all parties concerned, including private businesses.
2.4.3.3 Examples of Initiatives in the Designated Areas
Examples of planning projects on existing environmental conditions initiated in the designated areas are listed below:
Private-sector re-vegetation projects include a Tokyo Midtown Project in Roppongi, Tokyo (Figure I-31). In this project, extensive planting on unoccupied public land is planned to produce more cool air production areas.
Figure I-31 Tokyo Midtown Project (Roppongi)
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As shown in Figure I-32, the Osaki Station West Exit A zone was proposed to be redeveloped to actively introduce greenery along boundary walls.
Figure I-32 Redevelopment of the Osaki Station West Exit A zone
Apart from increasing vegetation areas in the city, there are also projects to address the UHI effect from the air ventilation aspects. One of them is to examine the implementation of ―wind or ventilation paths‖ for air breezes to pass through the city, to ensure sufficient wind paths in areas where major developments will be undertaken (including Shinagawa vicinity) (Figure I-33).
Figure I-33 Shinagawa
2.4.4 Lessons for Hong Kong
Hong Kong shares similar climatic characteristics with Tokyo, especially in the summer months, such as high temperatures and high humidity. In addition, fast urbanisation has led to high density of population and urban developments in both cities. The resultant urban climates are similar and both cities face similar problems. However, Hong Kong has a relatively hilly terrain that Tokyo does not enjoy. This necessiates the consideration of topography in the formulation of the Urban Climatic Map for Hong Kong.
The Thermal Environment Map of Tokyo is area-based, where climatically sensitive areas and problematic areas are shown on the map. Area-based guidelines are then generated to guide detailed studies. Each of these areas would mitigate UHI effect on a project-by-project basis. This approach enables the Thermal Environmental Map to be broadbrush, but still useful to guide urban design and planning.
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The Tokyo Environment Map does not take into account the Dynamic Potential of the city. It is therefore a simpler version of the German examples of UC-Map.
2.5 A SUMMARY OF GENERAL LESSONS LEARNT FROM CASE STUDIES
- There is a general global trend in the heightening of public awareness towards sustainability and environmental design of cities, with urban climatic issues becoming increasingly topical. The public is demanding more to be done.
- Increasingly, UC-Map is being used by governments for urban planning purposes. Based on the scientifically evaluated UC-AnMap, and the policy-based UC-ReMap, strategic planning and development proposals could be formulated.
- UC-Map is a ―synthetic‖ and ―evaluative‖, as opposed to an ―analytic‖, understanding of the factors and parameters affecting the urban environment. It attempts to define climatopes, and to balance, prioritise and weigh the combined effects of the parameters appropriately in view of the nature of the planning decisions that need to be made.
- UC-Map is useful in assisting planning decision-making, from the regional scale of 1:100,000 to the district scale of 1:5,000. UC-Map provides a holistic and strategic understanding upon which detailed and further site specific micro-scale studies could be identified and conducted.
- In Tokyo, the Thermal Environment Map with an emphasis on Thermal Load was created in 2002 to ―highlight‖ the 4 problem areas of the city that the Tokyo Metropolitan Government could focus its policies, investigations and actions to improve. In Germany, with more than 30 years of experience, the study of UC-Map is more sophisticated and has emphasised on Dynamic Potential and Wind Information factors.
- UC-Map should be a starting point to synergising the government and private sector‘s efforts towards better urban design. The making of climatic maps is not an one-off attempt but a continuous and long-term commitment.
- The making of UC-Map needs to call for participation of interdisciplinary experts from, but not limited to, climatologist, meteorologist, computer experts, architects, planners, development trade and the general public. The working of the UC-Map is
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also multi-disciplinary in nature. It works best with the concerted efforts of different disciplines under the lead of the planning authority, and with full political backup from the government.
- Holistic urban climatic consideration should eventually, in the intermediate term (about 5-10 years time), be attempted by combining various environmental factors such as air ventilation, solar radiation, noise, daylight, as well as air quality. This will allow a more comprehensive urban planning decision making process to take place.
- Public awareness on climatic issues could be raised. A concerted effort to inform and to educate is needed. Participation should be encouraged.
- Once the UC-Map is created, the process of improving and updating the UC-Map is on-going in nature. It requires professional monitoring on the use and the effectiveness of its application, as well as collecting further data as the basis of evaluation, updating of urban morphological data and refining the scientific basis as new knowledge develops.
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PART I(B): URBAN CLIMATIC ANALYSIS MAP FOR HONG KONG
1.1 INTRODUCTION
German and Japanese researchers have conducted pioneer work in the field of UC-AnMap and provided methodologies for implementation. In particular, the German guidelines VDI- 3787-Part1 (VDI, 1997a) and Part2(VDI, 1997b) are useful references for this study. When drafting the UC-AnMap for Hong Kong, the German experiences are evaluated and further refined taking into consideration of Hong Kong‘s unique urban morphology.
For example, in Germany, land use zone is typically used as input information for analysing building morphology and ground coverage in UC-Map. However, simply using land use information for Hong Kong may not be sufficient due to Hong Kong‘s more complicated and varied high density and high-rise urban morphology. It has been established early in the study that there is a need for further refinement and understanding of building volume density and ground coverage. Hence, instead of simply using land use zoning information, the UC- AnMap includes ―Building Volume Layer‖ and ―Ground Coverage Layer‖ to better suit Hong Kong‘s conditions.
The climatic data (from the HKO) and land use data (from the Planning Department) are key factors for creating the UC-AnMap for Hong Kong.
The following work procedure for this study is adopted:
Collate and evaluate existing data of Hong Kong ↓ Determining data layers of UC-AnMap ↓ Input information into the layer structure of GIS ↓ Evaluate classification categories of each layer ↓ Evaluate the positive and negative effects of all the layers based on Thermal Load and Dynamic Potential understanding to formulate the UC-AnMap ↓ Input Wind Information for air paths and air mass exchange understanding ↓ Final UC-AnMap ↓ Refinement and Verification
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On this basis, the framework of this study is presented below:
Urban Climatic Planning Recommendation Map
Methodology for Urban Climatic Map
1.1.1 Climatic Data
Air Temperature and wind data up to 2004 are provided by HKO in July 2005.
. Mean temperature by hour – 24 stations . Mean wind speed and direction by hour – 40 stations . Mean wind speed and direction by month – 40 stations . Wind roses – 40 stations
In addition to the data above, the study refers also to HKO‘s yearly summary of Meteorological Observation (from 1999 to 2006) and the MM5 simulation wind data by HKUST.
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1.1.1.1 Air Temperature
The HKO has an extensive network of weather stations around Hong Kong to collect various weather information (Figure I-34). An example of air temperature data from January to December based on HKO station data is shown in Figure I-35.
Figure I-34 Locations of HKO weather stations Monthly temperature data of Hong Kong
35
30
25
Max
20 C o Mean 15
Min degree 10
5
0 1 2 3 4 5 6 7 8 9 10 11 12 Figure I-35 An understating of Max., Mean andmonth Min. air temperature of Hong Kong from January to December based on HKO data (data from: http://www.weather.gov.hk/cis/normal/1971_2000/enormal01.htm)
The following understanding is based on a set of information provided by HKO in July 2005, containing mean temperature (by hour) for 24 stations (an example is shown in Table I-3):
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Base on an evaluation of the long term temperature data provided by HKO, it is noted that the summer months, especially June to August, have relatively high air temperatures. Further additional thermal (heat) load due to buildings will elevate air temperature. Moreover, the hourly temperature data provides an understanding of daily temperature variations. In general, urban air temperature is highest between 2 PM to 4 PM. As such, the study needs to focus more on this timeframe when evaluating the intra-urban climatic conditions in drafting the UC-AnMap.
Table I-3 A part table example of hourly mean temperature (July) ( HKO data)
The summer months are considered more critical for urban thermal comfort in Hong Kong, and the summer dataset is a key focus of the UC-AnMap. In contrast, Hong Kong has relatively mild winters (Table I-4), with January urban air temperatures of around 15 to 18℃. According to the result in the user survey conducted as part of the Study, the winter neutral PET (nPET) is lower, (at 14.6℃) under HK typical winter conditions. Around 70% of the surveyed subjects would express neutral Thermal Sensation (nTS) when PET is in the range of 14-16 ℃. Even at PET of 13℃ or lower, only 42% of the surveyed subjects express Thermal Sensation (TS)=-1 or lower (see Table I-5 for detail). For Hong Kong‘s typical mean winter air temperature of 16.3 ℃, assuming Tmrt of 17℃ (in shade), wind speed needs to exceed 3 m/s to result in PET of 13℃ or lower. Hence, apart from some exposed conditions in very windy days, thermal discomfort due to wind in the winter months is unlikely to be an issue, and this is the reason why the UC-AnMap focuses on summer condition for analysis.
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Table I-4 A part table example of hourly mean temperature (Jan) ( HKO data)
Table I-5 A part example of users thermal comfort survey result
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1.1.1.2 Wind Information
A. HKO Wind Data Wind data are currently available from 40 HKO stations (Table I-6), including information on wind roses by month, by season and annually. An example of the wind rose is shown in Figure I-36. Two examples of winds of stations by hour and by month are shown in Table I- 7 and Table I-8.
Table I-6 List of HKO weather stations
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Figure I-36 An example of wind roses provided by HKO
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Table I-7 A table of wind speeds and wind directions by hour provided by HKO
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Table I-8 A part table example of wind speeds and wind directions by month
In addition to the weather data, reference was made to meta-files of the stations provided by HKO. Of the 40 stations, data of 32 stations (excluding those on hilltop locations) are considered and expertly evaluated for the purpose of the UC-Map study. The HKO data of the 32 stations was collated spatially to gain information on: - main wind directions (annual wind rose and summer wind rose) (Figure I-37a and I-37b) - daily variations of wind directions
HKO stations are commonly located at exposed sites. As such, most wind roses from HKO are useful to evaluate background and regional winds synoptically. Although they typically represent the background conditions and not the urban climatic conditions, they can still be expertly evaluated to gain insight on land and sea breezes, thermal air mass movements, downhill air movements and topographical effects. The evaluation looks for characteristic patterns of wind flows so that air paths, air mass exchange, etc. that are useful considerations for urban climate could be assessed. The reasons for why they are enhanced or depressed by the prevailing wind can also be noted.
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Due to varying geographic and site conditions of the HKO stations (Table I-9), the stations should not be treated equally in a simple way. They could be used spatially to derive a set of wind information.
Table I-9 Meta information and an expert evaluation of 38 selected HKO station conditions and topographical information (with working note by Professor Lutz Katzschner (right column) when evaluating the data characteristics of the station (Figure IB-1) Keywords of Expert Evaluation of the station characteristics: Station No Height Sensor Code City structure Latitude N Longitude E C = City; R = Rural, A = air after map NN height path, T = thermal circulation B = background wind 1 Kings Park KP 64 89 Park in centre 22°18'47" 114°10'13" Urban park climate 2 HK Observatory HKO 31 73 City centre park 22°18'13" 114°10'19" Moderate city climate, does not represent dense intra-urban structures C 3 Int Airport HKKO 6 14 Airport 22°18'34" 113°55'19" Ventilation area, low roughness 4 Ta Kwu Ling TKL 12 27 Rural out territory far 22°31'50" 114°09'13" R north 5 Lau Fau Shan LFS 34 49 out terr north 22°28'14" 113°58'52" Rural climate, R 6 Shek Kong SEK 16 26 Out territory after 22°26'02" 114°05'06" Represents northern territory R mountain barrier (north) rural 7 Tai Mo Shan TMS 944 968 Mountain area north 22°24'40" 114°07'29" Mountain, no urban influence, background wind, B 8 Sha Tin SHA 5 16 Racecourse 22°24'11" 114°12'31" Air path, land sea breeze, A 9 Tates Cairn TC 575 588 Mountain barrier 22°21'34" 114°12'55" Background wind, B between HK and out territory 10 Sha Lo Wan SLW 58 70 Near airport island rural 22°17'28" 113°54'25" Dowhill air movements 11 Nei Lak Shan NLS 757 Island moutnain south 22°15'48" 113°54'40" Background wind, B 12 Cheng Chau CCH 71 98 Hill rural 22°12'04" 114°01'36" Island, no urban influence 13 Waglan Island WGL 55 82 Island reference station 22°11'01" 114°18'02" Island, no urban influence Background wind, B 14 Ping Chau EPC 29 39 Small island far away 22°32'54" 114°25'33" Island, no urban influence 15 Tai Mei Tuk PLC 55 70 Out territory lake 22°28'36" 114°14'06" No urban influence 16 Tap Mun TAP 24 37 Island in very north 22°28'22" 114°21'29" Island, no urban influence 17 Tsak Yue Wu TYW 5 22 Roof rural 22°24'11" 114°19'24" Rural /valley, R 18 Tseung Kwan O JKB 32 51 City with high buildings 22°18'56" 114°15'20" Valley 19 Tuen Mun TUN 62 69 City out terr west 22°23'32" 113°58'27" City climate; valley influence, C 20 Sai Kung SKG 3 30 City east near sea 22°22'38" 114°16'18" Land sea breeze effects 21 Ching Park House CPH 125 136 Bridge near harbour 22°21'00" 114°06'24" Channelling effects and thermal island winds, land and sea breeze effects, A 22 Wong Chuk Hang HKS 5 29 South HK island 22°14'54" 114°10'15" Southeast sea breeze effect T 23 Shell Tsing Yi SHL 33 42 Bridge 22°20'54" 114°05'02" No disturbance 24 Sha Chau SC 21 31 Island out west 22°20'45" 113°53'28" Island, land sea breeze T 25 Kowloon Tsai KLT 90 105 City with high buildings 22°20'12" 114°10'57" City climate, C 26 Cheng Sha Wan CSW 20 29 City near harbour 22°20'04" 114°09'05" City climate with sea breeze effects, C, T 27 Yau Yat Chuen YYC 40 64 Near city kowloon, 22°20'02" 114°10'13" City climate, C 28 Tai Mo To TMT 5 14 island 22°19'47" 113°58'00" Thermal induced circulation pattern, T 29 Kai Tak ICT 3 16 old airport 22°18'40" 114°12'39" Some land sea breeze effects, air path A, T 30 Siu Ho Wan SHW 0 14 Near road airport island 22°18'21" 113°58'45" Channeling effects, A 31 Star Ferry Pier SF 0 17 Sea side 22°17'35" 114°10'07" Land sea breeze effects 32 North Point NP 3 26 Pier HK island 22°17'40" 114°11'59" City climate, wind exposed C 33 Green Island GI 88 105 Island mountain 22°17'12" 114°06'37" Island, no urban influence 34 Star Ferry Central CEN 7 18 Pier centre 22°17'08" 114°09'31" Land sea breeze effects T 35 Central Plaza WCN 0 378 Tower HK island 22°16'53" 114°10'16" Urban overflow 36 Sham Wat SW 3 12 Sea shore near airport 22°16'07" 113°53'13" Influence from sea T island 37 Yi Tung Shan YTS 742 752 Highest mountain on 22°15'33" 113°57'51" Background wind B island south airport 38 Tai O TO 95 105 Island mountain top 22°15'22" 113°51'17" Influernce from sea T
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Figure I-37a An understanding of the territorial wind conditions based on annual wind roses of HKO stations – with topography background
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Figure I-37b An understanding of the territorial wind conditions based on summer (July) wind roses of HKO stations – with topography background
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B. MM5 Wind Data
The MM5 (i.e. Fifth-Generation NCAR/Penn State Mesoscale Model) is a regional mesoscale model which is applicable to many different types of atmospheric simulations, such as real- time regional weather forecasts, tropical cyclone prediction and climate change simulation. In this study, the MM5 simulation has been employed for investigating wind information (wind speed and wind direction) in Hong Kong for each and every month of the year 2004. The MM5 computer simulation was conducted by the Institute for the Environment in the HKUST (Yim et al., 2007). With acceptable accuracy, the grid size is 100 meters by 100 meters and the lowest level of height is 60 meters. This set of MM5 data provides a useful reference in the consideration of the prevailing winds in Hong Kong.
An example of wind rose presentation produced by MM5 simulation data has been shown in Figure I-38a. The wind rose has 16 directions which have finer directions compared with the HKO 12-direction wind rose. The corresponding MM5 wind roses have been presented for selected locations on the topographical map for the entire year of 2004 and the summer month of 2004 (July) respectively in Figure I-38b and Figure I-38c. The selected locations have been chosen to represent the HKO observation sites. By using the MM5 data and the HKO field measurements of winds data and considering the characteristics of Hong Kong climate, the prevailing wind directions will be identified and presented in this report.
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Figure I-38a An example of wind roses (MM5 simulation) provided by HKUST
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Figure I-38b An understanding of the territorial wind conditions based on annual (2004) wind roses of HKUST MM5 simulations – with topography background
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Figure I-38c An understanding of the territorial wind conditions based on the July (2004) wind roses of HKUST MM5 simulations – with topography background
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1.1.2 Topography, Urban Morphology and Greenery Data Topography, greenery, building and planning data are provided by the Planning Department (PlanD) in July 2006 and updated in 2009.
. DEM of Hong Kong topography in 2m by 2m grid . Land Use information . Buildings, including podium information, 2009 . Road information
1.1.2.1 Topography Hong Kong has a complex topography, which is hilly with high peaks (Figures I-39a and I- 39b). Apart from land formed by reclamation on both sides of Victoria Harbor, the only large areas of flat lands are in the northwest of the New Territories, which is far away from the city centre. Due to the surrounding topography, winds demonstrate differentiated patterns at different areas. Correspondingly, the urban pedestrian wind environment is influenced by the surrounding hills and slopes.
Most of Hong Kong‘s dense urban areas are located on land nearer to the sea level. Hence, temperature differential due to altitude may not be an important and useful consideration. Vegetated hill slopes next to urban areas can have beneficial thermal effects. Valleys can form useful air paths into the urban fabric. They should be mapped and considered.
Figure I-39a 3D Topography of Hong Kong
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Figure I-39b Contour of topography of Hong Kong
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1.1.2.2 Urban Morphology Local microclimate is heavily influenced by the ―structure‖ of the city (Givoni, 1998). Accordingly, the urban geometry and profile, including height, building sizes, building shape, etc, all have an impact on the urban climate.
Hong Kong is an extremely high-density city with a population of about 7 million people living within 1,100 square kilometres of land (Figures I-40a and 40b). In some areas of Hong Kong, the urban density can exceed 60,000 persons per square kilometer. This compact urban form of Hong Kong originates from its topographical constraints and shortage of land for development. The general urban characteristics of high-rise and high-density buildings are summarised below:
Densely packed buildings with narrow streets in between Construction materials of very high heat storage capacity Very high degree of impervious horizontal surface (asphalt, concrete, cement, stone paving) The street block geometry generally traps radiation and creates stagnation Very tall and sharp edged buildings Very low density of vegetation within the urban environment High levels of heat and anthropogenic waste heat from human activities
Figure I-40a A typical densely built urban area in Hong Kong
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Figure I-40b Extract of Building Volume Map of urban Hong Kong based on the building data from PlanD
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1.1.2.3 Greenery
Figure I-41 Map of Greenery in Hong Kong based on NVDI image (Courtesy of Prof. Janet Nichol)
Greenery area can affect the surrounding air temperature, solar exposure of pedestrians, and the wind speed in the streets. To be precise, vegetation mitigates Thermal Load not by cooling the air, but by warming the air less (Kurn et al., 1994). Some studies (Gόmez et al., 1998) have investigated the microclimatic effects of vegetation on mitigating the negative Thermal Load of the urban environment. Shashua-Bar and Hoffman‘s study (2000) found that the effect is not only confined within the green area, but extends beyond itself. Its cooling effective area is perceivable up to 100m from the boundary depending on the surrounding obstructions. Dimoudi and Nikolopoulou (2003) also confirmed the same result.
Natural greenery bordering urban areas, as well as parks and greenery within the urban fabric need to be considered. In addition to PlanD‘s land use data, we have obtained a NVDI (The Normalized Difference Vegetation Index) image from the Hong Kong Polytechnic University for analysis. The NVDI image is created from an ASTER image taken at October 2005 (Figure I-41).
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1.2 KEY ANALYSIS
For generating the UC-AnMap, three key levels of analyses are needed.
1.2.1 Thermal Load
Thermal Load measures the stored or emitted heat intensity of particular localities of urban areas and it mainly depends on the building volume (which has an impact on heat storage, and blocking the sky view, and slowing the city‘s cooling at night), the topography and the availability of green spaces for cooling effect.
Thermal Load can be defined as the intra-urban air temperature variations due to the urban forms and surfaces (Evans, 1996). A key problem of urbanisation is the Thermal Load it generates due to buildings and artificial/man made surfaces. The Thermal Load is considered to be the main reason of the intra-urban temperature rises. For Hong Kong‘s hot and humid sub-tropical climatic conditions, Thermal Load adds to heat stress in the summer months. Inhabitants of the city are less likely to feel comfortable outdoor. In addition, energy consumption within buildings would increase.
1.2.2 Dynamic Potential
Dynamic Potential evaluates the ground roughness and therefore the availability of wind and cold air mass exchange of particular localities of urban areas. It mainly depends on the site coverage, availability of natural landscape on slopes, and proximity to openness.
Air Ventilation is an effective way to mitigate the adverse effects of Thermal Load as it carries away the excessive heat of the city, replacing it with cooler ambient air (Golany, 1996; Kuttler, 2002; Weber & Kuttler, 2003). Air movement in hot and humid summer months of Hong Kong could also help reduce heat stress and improve human thermal comfort.
1.2.3 Wind Information
Wind Information gives the background wind speed and direction information at above urban canopy layer (UCL) level, taking into account the surrounding topography. It allows air paths and air mass exchange to be understood. For this study, MM5 simulated wind information data (summer and annual) will be collated, evaluated and considered.
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The considerations of Thermal Load and Dynamics Potential are urban morphologically- based. They depend on buildings on ground, greenery and topography etc. Wind Information allows main air paths and air mass exchange to be identified. For preparing UC-AnMap, researchers rely on observatory station data, as well as simulated data, if necessary.
1.3 UC-ANMAP AND PET
The consideration of Thermal Load and Dynamic Potential need to be brought together to become the draft UC-AnMap (without Wind Information). It is noted that the use of a human urban thermal comfort indicator as a synergistic element to collate the UC-AnMap of Hong Kong seems to be appropriate. This study uses Physiological Equivalent Temperature (PET)(Höppe, 1993, 1999) as the said indicator. It is an index widely used to understand the thermal comfort environment of outdoor spaces.
‖Physiological Equivalent Temperature (PET) is the temperature of a reference environment based on a heat balance model that combines various climatic and physiological variables including air temperature, relative humidity, solar and environmental radiation, air movement, clothing and metabolic rate to give a synergetic indication of human thermal comfort.‖
Based on the magnitude of a parameter (e.g. land use, building volume or green space) for increasing or decreasing PET, the classification values could be defined on the UC-AnMap. This allows a balanced and synergetic consideration in formulating the UC-AnMap when all the parameters are collated. It is assumed that a parameter increase of the PET value by at most 1 ℃, would lead to the parameter being categorised as 1 class. For example, taking the Building Volume as a parameter, the variation of Thermal Load due to different volumetric heat capacity of the buildings can attain the PET value of up to 5℃, hence the parameter would have 5 positive categories from 1 to 5.
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40 34
35 32
30 30
28 PET(Deg C) PET(Deg 25 C) (Deg PET 26
24 20 22
15 20 20 22 24 26 28 30 32 34 0 0.5 1 1.5 2 2.5 3 3.5 4 Ta (Deg C) Wind (m/s)
(a) PET vs. Air Temperature (b) PET vs. Wind Speed Figure I-42 The relationship between PET and the urban climatic factors (Air Temperature and Wind Speed)
According to the study on the relation between PET and its environmental factors, especially air temperature and wind speed (Figure I-42), it is found that an increase of air temperature by 1℃ corresponds to the PET value rising at about 1℃. But the PET value is inversely proportional to the wind speed, i.e. an increase of wind speed from 0.5 to 1.5 m/s has an effect of decreasing PET by about 2 ℃.
Hong Kong is located in the sub-tropical climatic zone with hot summer months and mild winter months. Based on the technical input of outdoor thermal comfort study of Hong Kong, it is found that at a typical summer temperature of about 28℃, more than 75% of the people surveyed reported a thermal sensation of warm, hot or too hot. Whereas at a typical winter temperature of about 15℃, less than 21% people reported a thermal sensation of slightly cold and only 2% reported cold. Hence, for urban thermal comfort, the problems in Hong Kong are in the hot and humid summer months – June, July and August. For this reason, a UC- Map of summer conditions would be more important and relevant, as far as wind and urban thermal comfort are concerned.
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1.4 DATA COLLECTION AND PROCESSING
The principle of the proposed methodology consists of mainly an evaluation and classification system of the urban climatic conditions. The method is to first transform urban climatic conditions into a 6-layer classification system, in which various parameters for Thermal Load and Dynamical Potential are designated. With the aid of GIS, climate-relevant land use, building and topographical data from the Planning Department are stored, calculated, classified, and combined by using a synthetic method. With this layered structure of information (as illustrated in Figure I-43), the model could easily be updated, added and modified.
Buildings Landuse Topography
Building Volume Topography Green Space Ground Coverage Natural Landscape Proximity to Openness
+
Thermal Load Dynamic Potential
Draft UC-AnMap Wind Information Final UC-AnMap
+ =
Figure I-43 An Illustration of Workflow for Creating the UC-AnMap (100m x 100m raster based)
Creation of the UC-AnMap for Hong Kong requires various meteorological data and planning data provided by the HKO and the Planning Department respectively. Meteorological data are used for climatic evaluation, while planning data are extensively used in the GIS analysis.
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1.5 LAYERS AND THE CLASSIFICATION SYSTEM
The urban climate of the city can be characterised with a balanced consideration of ―negative‖ effects, i.e. the Thermal Load (e.g. building bulks) and ―positive‖ effects, i.e. mitigation factors to reduce Thermal Load (e.g. green spaces) and promote Dynamic Potential (e.g. air ventilation).
The layering structure of the UC-AnMap is in Table I-10.
Table I-10 Overview of GIS layers for the UC-AnMap
Physical Criterion Effect Scientific Basis Input layers
Layer 1 Negative Building bulk Building Volume Map
Layer 2 Thermal Load Altitude and Elevation Topographical Height Map Positive Layer 3 Bioclimatic effects Green Space Map
Layer 4 Negative Urban permeability Ground Coverage Map
Bioclimatic effects Layer 5 Dynamic Potential - Cold air movement Natural Landscape Map Positive Air mass exchange and Layer 6 Neighbourhood effects Proximity to Openness Map
Layer 7 MM5 Simulation and Not Wind Information Layer Wind Information HKO field applicable － Prevailing Wind Directions measurement (Summer)
A classification system of each of the respective layer is drawn up based on the ―UC-AnMap and PET‖ relationship as outlined in Section 1.3. For each layer, the characteristics of the concerned physical criteria are classified. The classification values are basically a numerical assignment (positively and negatively) of the factor‘s likely physical effects to the urban climate.
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The value is assigned according to their probable degrees of effects on increasing or decreasing the PET values. Positive numbers are assigned when the categories would add to the PET values. Negative numbers are assigned when the categories would lower the PET values.
When the classification values of all the layers are collectively considered, the UC-AnMap is then generated. In short, six layers have been examined for determining Thermal Load and Dynamic Potential, with Layer 6 containing three sub-layers. Layer 7 is to examine the wind information and it does not have an effect in determining Thermal Load and Dynamic Potential.
Layer 1 – Building Volume Map Buildings store a significant amount of the solar energy received which elevates the temperatures (surface and air) of the city, especially at night when it is released back to the sky. A principal cause of high Thermal Load is the blocking of sky view by buildings which reduces cooling in the night time. Buildings built close together block each others the amount of heat energy that could be released back to the atmosphere. 6 classification values are assigned, ranging from ―Very High heat capacity‖ to ―No Building‖.
Layer 2 – Topographical Height Map In general, air temperature varies according to altitude; with higher ground being cooler than the lower ground. 4 classification values are assigned, ranging from ―Low topographical height‖ to ―Very High topographical height‖.
Layer 3 –Green Space Map Green area can affect the ground air temperature. Vegetation has a cooling potential to the city and thus mitigate the adverse effects of Thermal Load. 2 classification values are assigned, ―No‖ and ―Yes‖.
Layer 4 – Ground Coverage Map The amount of land occupying by buildings is known to be directly related to the wind permeability of the location. In general, a neighborhood with higher ground coverage (by buildings) will have lower Dynamic Potential. 3 classification values are assigned, ranging from ―High‖ to ―Low‖.
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Layer 5 – Natural Landscape Map Natural vegetation (together with slopes of the hill (Layer 6)) creates cooler air movement. This has a cooling potential to the city. 2 classification values are assigned, ―Woodland‖ and ―Urban area and Grassland‖.
Layer 6 – Proximity to Openness Map The dynamic movement of air ventilation always mitigates the adverse effects of Thermal Load. There are 3 sub-layers that are important in this regard.
. Layer 6a – Proximity to Waterfront Map Land and sea breeze is an important consideration for coastal areas. In general, the benefits of sea breeze depend on the location‘s distance from the sea. 3 classification values are assigned.
. Layer 6b – Proximity to Open Space Map Urban open space can benefit its surrounding areas. 2 classification values are assigned.
. Layer 6c – Slope Map Cooler air moves downhill and in general along the valleys. This cooler air is beneficial. 2 classification values are assigned.
Layer 7 – Wind Information Layer – Prevailing Wind Directions (Summer) In addition to the 6 layers above, Layer 7 is included to give key wind direction and speed information for the prevailing winds of different parts of Hong Kong in the summer.
The UC-AnMap of Hong Kong Based on the scientific understanding of ―positive‖ and ―negative‖ effects, 8 classifications have been identified and they are collated to become the UC-AnMap for Hong Kong at a grid resolution of 100m x 100m.
1.5.1 Thermal Load
Thermal Load has two effects which are considered to be the important factors in creating the UC-AnMap for Hong Kong. If the site contains high heat storage such as large building bulks, then its has ―positive‖ Thermal Load, i.e. an increase in PET value, which is presented in Layer 1. In contrast, higher altitude and greening have ―negative‖ Thermal Load, i.e. a
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Layer 1 – Building Volume Map Description: Urban geometry has a complex influence on the microclimate of the urban environment. For example, difference between urban geometry and building density may result in intra-urban air temperature differences (Chandler, 1965; Eliasson, 1990-1991; Oke, 1987). High building volume not only increases the localised heat capacity (i.e. Thermal Load), but also reduces the Sky View Factor7 (SVF) which is a major influence of slowing the radiative cooling effect in city at night. The most important aspect of this effect is that built-up areas predominantly obstruct the open sky and delays the cooling of the surface during clear, calm nights (Oke, 1981). If the building volume density is high, the long-wave radiation could be blocked and the energy would be released back into the sky more slowly. Therefore, the cooling process within the city centre tends to be slower than its surrounding areas leading to relatively higher temperatures.
In short, the higher the building volume density, the larger the heat capacity, which in turn, is significant to the increase of Thermal Load. Urban density is also a major factor to determine the urban ventilation conditions and the urban temperature. In general, an urban area having higher density of the buildings would experience a poorer urban ventilation condition and a stronger UHI effect (Givoni, 1998; Hui, 2001).
In warm and humid regions such as Hong Kong, these conditions would elevate the level of thermal stress experienced by residents (Leung et al., 2008; Ng, 2009). To aggravate the problem, the heat produced by air conditioning raises the urban air temperature yet further and thus reinforces the Thermal Load. Since wind is one of the major driving force to mitigate the effect of Thermal Load, the density of building blocks also significantly affects the local micro-wind environment (Niu, 2004). As a result, high building volume is a major contributor to Thermal Load.
For the past three decades, researchers have attempted to analyse the temperature variation in particular to urban street canyons caused by the urban geometry, i.e. the height-to-width ratio
7 Sky View Factor (SVF) is a measure of the degree to which the sky is obscured by the surroundings for a given point. In urban climatology, it is mainly used to characterize the geometry of urban canyons. Its value is a ratio ranging from zero to one. When obstacles fully block the sky, the factor is zero. When the sky is completely visible, the factor is one..
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(H/W) and SVF. Oke (1981) first developed a scale model to evaluate the role of building geometry on the UHI effect. He showed that the UHI effect is directly related to the SVF, as it controls the rate of the radiative cooling at street level within the city.
On the other hand, many studies (Barring & Mattsson, 1985; Eliasson, 1990/91; Goldreich, 1992; Montaveza et al., 2008; Svensson, 2004a; Unger, 2004; Unger, 2009; Upmanis & Chen, 1999b) have demonstrated that the relationship between H/W ratio and SVF can be employed as a measure of urban geometry. This shows the trends and variations of air temperature in urban and in rural areas. A longitudinal review was given in Unger (2009).
Lindberg (2007) has also demonstrated that the areal mean of SVF (r = 100 m) is highly correlated to the intra-urban air temperature variations, but is relatively less correlated to the SVF taken from a point source location. The usefulness of areal mean of SVF was further proven by Gal et al (2009). It is important to apply this relationship to urban planning and urban design in order to mitigate the UHI effect. A preliminary investigation of the relationship between SVF and UHI in Hong Kong was given in Chen and Ng (2009; 2010). In this study, the SVF is employed as a means to reflect the building volume information.
Input Data: Buildings data (bldg_merge.shp; pod_merge.shp), DEM data (hk2mgrid raster) and Land Use data (final_2005_20060710.shp).
Methodology: This layer is derived from knowledge-based processing.
The land use in Hong Kong has been considered in both Layers 1 (Building Volume Map) and 4 (Ground Coverage Map). As discussed, building volume is a major factor of heat capacity and temperature variation in urban areas.
Layer 1 contains the building volume information area in grid size of 100m x 100m resolution and volume is in cubic meters. However, in the GIS model the building volume values have to be converted to percentages of the highest volume grid which is found in the region. 6 classification values are assigned and ranged from ―no buildings‖ as ―0‖ to ―more than 25 % of maximum building volume‖ as ―5‖ (Table I-12).
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The linear relation between SVF and temperature variation has been adopted (Brown et al., 2001; Eliasson, 1990-1991; Svensson, 2004b; Upmanis & Chen, 1999a; Voogt, 2007). Our parametric model reveals a logarithmic relation between building volume (BV) and SVF, i.e. SVF c* BV
This forms the basis for the threshold value of the classification value in Layer 1. It is noted that the SVF is evaluated based on the method proposed by Eliasson and Svensson (2003). The calibration of the SVF is carried out by the field measurement and SVF simulation for the Tsim Sha Tsui area (Figure I-44). Hence, the proposed formula for the temperature variation and the SVF is as follows: T 4.18 9.09 SVF
Some numerical results for the above formula are presented in Table I-11.
Table I-11 T-SVF-Building Volume relation for selected points in the field measurement T (°C) SVF Building Volume (%) 28.2 0.59 2.0 29.2 0.33 6.0 30.7 0.22 12.8 31.8 0.07 21.6
Tref = 28 °C
Figure I-44 SVF classification of Tsim Sha Tsui
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Based on Table I-11 and the SVF map above having the designated threshold values (4%, 10% and 25%), a further calibration for the building volume classification was made (Chen et al., 2010) to further refine the building volume classification map, to be consistent with the field measurement results.
GIS Operation Procedures: 1. Derive the correct absolute building height from the value of building top and building base by: a. Converting DEM file of topography height to 10mx10m shapefile b. Spatially join the shapefile of topography height to building/podium shapefile c. Use the resultant field as a new base and calculate the absolute building height by setting ―height=top-base‖ 1. Convert the newly joined building and podium shape file to raster file, i.e. raster value = height of 1m x1m resolution; 2. Merge the building and podium raster file by using the ‗mosaic‘ function and select ‗maximum‘ as the option; 3. Aggregate the resulting raster file into a 100m x100m resolution by using the ‗sum‘ option, where the highest value is chosen to be 1,200,000m3 = 100%, being the highest building volume value based on 2006 dataset. This is adopted as the basis for the UC- AnMap calibration; 4. Divide the raster by the highest value using ‗Raster calculation‘; 5. Classify the result into 5 classes (0%, ＞0%~4%, 4%~10%, 10%~25%, and greater than 25%); 6. Use the Land Use shape file to select ‗no building but concrete areas‘ and convert to raster of 100mx100m resolution; 7. Use ‗mosaic‘ to add the new raster to the result, choose ‗last‘ option; 8. Reclassify and define classification value.
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Result:
Layer 1- Building Volume Map
Figure I-45 Building Volume Map
Table I-12 The Classification of Layer 1 Building volume Tentative Classification Thermal Load (percentage range) (%) Value Zero 0 (no building) 0 Very low 0 (paved area only) 1 Low >0 – 4 2 Medium >4 – 10 3 High >10 – 25 4 Very high >25 5
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Layer 2 – Topographical Height Map
Description: The environmental lapse rate demonstrates that air temperature decreases with height at a rate of approximately 10°C per km (Golany, 1996). Being a relatively hilly city, the topography is therefore an important factor when dealing with Thermal Load in Hong Kong.
The environmental lapse rate changes the sensible thermal load of a region. In general, the higher the elevation, the greater the wind speeds as the magnitude of the wind in the free atmosphere is uniform (Aronin, 1953). The upper level wind is generally not affected by ground roughness, such as man-made structures. In her studies, Svensson and her colleagues (2003) had recorded the highest wind speeds at the high altitude district.
The variation of air temperature depends on the characteristics of the ground surface. In Hong Kong, the local topographical features modify the thermal load in the urban environment. The local wind is accordingly affected by the altitude of the region.
Input Data: DEM data (hk2mgrid raster).
Methodology: This layer is derived from knowledge-based processing.
Layer 2 represents the topographical height in meters according to the Digital Elevation Model provide by the Planning Department. Gridharan (2005) had thoroughly studied the Hong Kong UHI and suggested that at a level of 10 m above sea level, altitude has a marginal influence on daytime and nocturnal UHI. However, beyond the threshold level of 10 m, altitude differences will produce rather substantial changes in both daytime and nocturnal UHI. As such, it is reasonable to group those areas of topographical heights of less than 10 m above sea level as one area, where UHI is more significant than higher levels.
Between 200m and 300m above sea level (which is above the urban canopy layer), the wind profile will be less influenced by urban structures. Besides, the UC-Map for Hessen (MRD, 1996) had found that the UHI effect is much more severe in areas of lower topographical height, so the threshold classification value is not chosen linearly. Based on expert evaluation, 4 classification values are assigned, ranging from ―Low topographical height‖ to ―Very high topographical height‖ (Table I-13).
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GIS Operation： 1. Aggregate DEM data to 100 m resolution, using ‗mean‘ option; 2. Reclassify and define classification values: assign -3 for greater than 400 mPD, -2 for >200 – 400mPD, -1 for >50 – 200mPD and 0 for 0 - 50mPD.
Result:
Layer 2- Topographical Height Map
Figure I-46 Topographical Height Map
Table I-13 The Classification of Layer 2 Topographical Tentative Classification Topographical Height (mPD) Height Value Very high >400 -3 High >200 – 400 -2 Medium >50 – 200 -1 Low 0 – 50 0
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Layer 3 – Green Space Map
Description: Green space represents well-vegetated areas covered by trees or grasses etc. The process of evapotranspiration in plants absorbs large amount of heat from the air which cools the surrounding air temperature. In general, vegetations absorb a substantial proportion of infrared radiation but reflect most of the near-infrared radiation during the process of photosynthesis. The absorbed energy by the vegetation then evaporates waters on the surface of the leaves (Dimoudi & Nikolopoulou, 2003; Miller, 1997). Many studies have shown that greenery is an important factor in dealing with Thermal Load (Ali-Toudert & Mayer, 2007; Ca et al., 1998; Chudnovsky et al., 2004; Emmanuel et al., 2007; Fahmy & Sharples, 2009; Gao, 1993; Shashua-Bar & Hoffman, 2000, 2004; Spangenberg et al., 2008; Yu & Hien, 2006). In urban areas, besides reducing the surrounding air temperature, green space also provides shading for pedestrians on sunny days, and can affect the wind speed in the streets (Givoni, 1998).
It is estimated that for every 100 m2 of vegetation added to a park, it can effect a 1 °C decrease in air temperature (Dimoudi & Nikolopoulou, 2003). Shashua-Bar and Hoffman‘s (2000) investigated that the green space effect contributes about 0.5°C cooling of the air temperature comparing to the shading effect. In Gao‘s model (1993), for the case of bulk ratio 600% and road ratio 20%, 30% green area can reduce the air temperature by nearly 1 oC and 50% green area by nearly 2 oC. Based on multi-regression analysis of all the simulation results, out of three effects of bulk ratio, green land and artificial heat release, the coverage ratio of ground space greatly influences the average and maximum air temperature, with relatively weaker influences on the minimum air temperature. According to another study by Dimoudi and Nikolopoulou (2003), doubling the size of the park can reduce air temperature by 1 oC, whilst tripling the size of a park leads to further reduction of air temperature by 1.5 – 3 oC. Moreover, as the H/W ratio increases, the wake effect increases too and therefore, mixing of air is reduced, which keeps the effect of the park relatively local. Overall, as a rule of thumb, a 0.8 oC reduction in ambient air temperature is to be expected for a 10% increase to the ratio of green to built area, for the urban fabric under consideration in the study.
Moreover, this cooling effect can extend beyond the subject green space. According to field measurements by Saito(1990/91) in Kumamoto, Japan, high temperature regions were found in the dense built environment. The higher the ratio of the green area, the lower the air temperature. Even small green areas (60mx40m) show a remarkable cooling effect. It was found that the maximum temperature difference between the small green area and its surroundings was 3ºC.
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The green space effect provide a positive mitigation for Thermal Load. Urban planning and design should therefore seriously consider greening as a key strategy for pursuing a better urban living environment (Shashua-Bar & Hoffman, 2000). Research work led by the US government suggests that air ventilation can be greatly enhanced with the use of vegetation, which can be used to redirect the air flow and create channeling effect in order to reduce the air temperature (Hebert & Rouge, 1991).
Input Data: NVDI (Normalized Difference Vegetation Index) image from ASTER image taken in 2005 October (NVDI.tiff)
Methodology: This layer is derived from knowledge-based processing.
Layer 3 is about green space which is created from the NVDI dataset. The thresholds of the NDVI image are listed below: NDVI<=-0.1: urban/ bare soil; NDVI>-0.1: vegetation, where NDVI>0.6: tree -0.1
GIS Operation： 1. Import the NVDI dataset into ArcGIS and convert it to raster format; 2. Reclassify the raster, NVDI<=0.1 0, NVDI>0.1 1; 3. Resample the raster in the previous step to 1m resolution; 4. Aggregate the raster in the previous step, option = ―SUM‖; 5. Reclassify the raster in the previous step, value<=3300 0, value>3300 -1.
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Result:
Layer 3 - Green Space Map
Figure I-47 Green Space Map
Table I-4 The Classification of Layer 3 Tentative Classification Green Space Value Yes - 1 No 0
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Layer TL –Thermal Load Map
By adding the specific classification values of the above 3 layers (Layer 1, Layer 2 and Layer 3) at each grid (Figure I-48a), the classification values for the composite layer of Thermal Load are derived, (shown in Figure I-48b).
Input Data: Building Volume Map (Layer 1), Topographic Height Map (Layer 2) and Green Space Map (Layer 3).
Methodology: This layer is derived from raster-based calculation.
GIS Operation: 1. Use ‗raster calculation‘ to sum up Layer 1, Layer 2 and Layer 3 and the result is in 100mx100m resolution;
Thermal Load Map
(a) Layer 1 (b) Layer 2 (c) Layer 3 Figure I-48a Components of Thermal Load Map
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Figure I-48b Layer of Thermal Load of the UC-AnMap
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1.5.2 Dynamic Potential Apart from Thermal Load, Dynamic Potential is also an important factor that is required to be taken into consideration for climatic effects.
Layer 4 – Ground Coverage Map
Description: The performance of air ventilation is one of the key considerations in urban planning and building design. Oke (1987) first provided the logarithmic wind profile in a thermally neutral atmosphere. In general, urban built-up structures can affect this wind profile by obstructing the local wind in both horizontal and vertical sense, and also block the outlet for air circulation (Landsberg, 1981; Murakami et al., 1999; Perry et al., 2004).
Hence, reliable evaluation of the aerodynamic characteristics of urban areas is significant to depict and predict the urban wind behaviours (Grimmond & Oke, 1998). There are several morphological empirical models established to estimate such aerodynamic characteristics of urban areas (Bottema, 1996; Kutzbach, 1961; Lettau, 1967; Macdonald et al., 1998; Raupach, 1992). Coupling with a spatially continuous morphological characteristics database, such morphological estimation models help planners and researchers to depict the surface roughness of urban areas (Gál & Sümeghu, 2007; Ratti et al., 2002).
In this layer, the amount of ground coverage is expressed in terms of a Ground Coverage ratio of the actual ground floor areas of the buildings physically occupied in a locality. This can be an indicator of urban permeability.
Ground Coverage ratio represents the density of built-up areas; the greater the Ground Coverage, the lower the wind speed. Ground coverage has been adapted as a useful indicator of the intensity of UHI and the value of wind velocity ratio (Kubota et al., 2008). Yoshie (2006) investigated the relationship between the gross building coverage ratio (similar to Ground Coverage) and the wind velocity ratio for cities. His findings showed an inversely proportional relationship (Figure I-49), where low building coverage will experience a high wind velocity ratio, and vice versa. In this subsequent study, we have utilised Yoshie‘s (2006) study by extrapolating additional data points (Table I-15).
The two-dimensional Ground Coverage ratio, which is readily available, can be used to predict the area average pedestrian level urban ventilation of the city (Ng et al., 2010).
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Extensive studies have been conducted to identify the cause of air ventilation degradation by the Ground Coverage ratio. The aim of the studies is to improve outdoor thermal environments (Barlow & Belcher, 2002; Cook, 1978; Davenport, 1961; Jensen & Franck, 1965).
Figure I-49 Relationship between Gross Building Coverage Ratio and Wind Velocity Ratio (Modified from Yoshie 2008)
Table I-15 Estimation of wind velocity (Based on Yoshie (2006) analysis) Gross Building Coverage (%) VR V (m/s) 0 - 30 ~ 0.2 ~ 2 >30 - 50 ~ 0.15 ~ 1.5 >50 <0.1 <1
Input Data: Buildings data (bldg_merge.shp; pod_merge.shp) DEM data (hk2mgrid raster) Land Use data (final_2005_20060710.shp)
Methodology: This layer is derived from knowledge-based processing.
To study the characteristics of the land use in Hong Kong, in addition to Layer 1 (Building Volume Map), Layer 4 (Ground Coverage Map) has to be investigated. Layer 4 fully integrates information on building coverage with ground roughness, by illustrating the extent of building form within the city.
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This map is calculated from two original government data sets from, namely, building data and podium data in vector formats. Figure I-50 shows the results of conversion from shape file to 1mx1m raster. The raster files store information of built-up areas in matrix which are combined to form a larger grid of 100m x100m; the built-up area within each 100m x100m grid is then calculated. Three classification values are assigned (Table I-16).
Building A Grid area storing
Podium ground area coverage value Built-up areas
Figure I-50 Creation of Ground Coverage Map using GIS
GIS Operation: 1. Merge building and podium shape files by using ‗Union‘ function; 2. Add a new field ‗Cover‘ of the resulting shape file and set ‗Cover = 1‘; 3. Convert the shape file to a 1mx1m resolution raster file and set ‗raster value = cover‘; 4. Aggregate the raster to 100mx100m resolution; 5. Use ‗raster calculation‘ to divide the raster value by 10,000 to get the ground coverage percentage value; 6. Reclassify and define classification values.
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Result:
Layer 4 - Ground Coverage Map
Figure I-51 Ground Coverage Map
Table I-16 The Classification of Layer 4 Ground Coverage Air Ventilation Ground Coverage Tentative Classification (Buildings) Potential (%) Value Low High 0 -30 - 2 Medium Medium >30 – 50 - 1 High Low >50 0
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Layer 5 – Natural Landscape Map
Description: Natural vegetation can promote and facilitate movement of cold air, which is important in understanding Dynamic Potential. Research work have been extensively conducted to study the differences in surface roughness in affecting the wind velocity within the urban environment (Bowne & Ball, 1970; Brook, 1972; Landsberg, 1981; Oke, 1987, 1988).
The greenery area has lower roughness length than the built-up areas. Table I-17 shows the aerodynamic properties of natural and building surfaces (Oke, 1987).
Table I-17 Aerodynamic properties of natural and building surfaces (altered from (Oke, 1987) and (Landsberg, 1981)) Roughness length, Surface Remarks Z0 (m) Water Still-open sea 0.000001- 0.00001 Sand, desert 0.0003 Soil 0.001- 0.01 0.02- 0.1m 0.003- 0.01 Grass 0.25- 1.0m 0.04- 0.10 Deciduous 1.0 - 6.0 Forest Coniferous 1.0 - 6.0 Building 1.5 - 5
Input Data: NVDI (Normalized Difference Vegetation Index) image from ASTER image was taken in Oct 2005. The image of NVDI is in tiff format.
Methodology: This layer is derived from knowledge-based processing.
Layer 5 is a correction of Layer 4 with regard to roughness length, because in Layer 4, trees and grass are treated indiscriminately which overestimates the Dynamic Potential of trees. For calculation purpose, the urban area is assigned zero value since it is not to be considered in this layer. The following section explains the reason for the overestimation.
Oke (1987) showed that the wind profile has similar structures above city centres, woodlands or the suburban areas. This is evident by the similar roughness lengths listed in Table I-17. However, for land having low-roughness such as grassland, the wind profile shows some
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Z VVforest 0 ln Z forest and Z VVgrass 0 ln Zgrass
For a conservative estimation, assume Z forest 1 m, Zgrass 0.1 m, and the friction velocity
V0 0.5 m / s , at the level of Z = 2 m, the velocity difference between grassland and woodland is approximately 1 m/s. This is the basis of our classification.
In Layer 4, vegetation including both tree and grass has the classification value of -2, so in Layer 5, a correctional reclassification value of +1 will be added to trees indicating lower Dynamic Potential compared to grass. The conventional threshold of 75% is used to determine whether a grid is woodland or not. Two classification values are also assigned (Table I-18).
GIS Operation: 1. Refer to Green Space Map (Layer 3); 2. Reclassify NVDI raster image, NVDI<=0.6 0, NVDI>0.6 1; 3. Resample the raster in the previous step to 1m resolution; 4. Aggregate the raster in the previous step, option = ―SUM‖; 5. Reclassify the raster in the previous step, value<=7500 0, value>7500 1.
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Result:
Layer 5 - Natural Landscape Map
Figure I-52 Natural Landscape Map
Table I-18 The Classification of Layer 5 Tentative Classification Natural Landscape Value Woodland 1 Urban area and grassland 0
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Layer 6 – Proximity to Openness Map
Introduction: The location of buildings may affect wind penetration into a certain area. Proximity to open sea or open land is a key factor in understanding Dynamic Potential. Field measurements showed that there is an interaction between open landscape and urban areas due to the unique condition of Hong Kong. Layer 6 consists of 3 Sub-layers, namely, Layer 6a: (Proximity to Waterfront Map), Layer 6b (Proximity to Open Space Map) and Layer 6c (Slope Map).
Layer 6a – Proximity to Waterfront Map
Description: In constructing large-scale climatic maps (Svensson et al., 2003), the distance measured from the coastline for sea breeze is a major consideration. Similar to Layer 4 (Ground Coverage Map), differences in roughness length result in different wind conditions.
Input Data: Land use data (final_2005_20060710.shp) Ground Coverage Map (Layer 4).
Methodology: This layer is derived from knowledge-based processing.
Sub-layer 6a shows proximity to waterfront characteristics in Hong Kong. Three classification values are assigned (Table I-19). Seashore areas are classified and assigned the value of ―-2‖ or ―-1‖ or ―0‖ according to their distance to the sea. A logical function is established using Ground Coverage information as a criterion determining whether or not to assign the value. The logical function applied to a grid (i) of 100m x 100m resolution is as follows: If Layer4(i) = -2 (Ground Coverage <= 30%): o If D(i) < 70: raster value = -2; o If 70<=D(i)<=140: raster value = -1; o If D(i) > 140: raster value = 0; If Layer4(i) = -1 (30% < Ground Coverage <= 50%): o If D(i) < 70: raster value = -1; o If D(i) >= 70: raster value = 0; If Layer4(i) = 0 (Ground Coverage > 50%): raster value = 0.
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT where Layer4(i) is the pixel value of grid (i) in Layer 4, and D(i) is the distance of pixel (i) from the sea. This logical function is implemented as a macro embedded in ArcGIS. Large water bodies are assigned the value of -1. Three classification values are assigned (Table I- 19).
GIS Operation: 1. Select coastline data (Hong Kong and portion of China) from the land use data; 2. Use ‗buffer‘ function to buffer it twice (-70 m and -140 m) and two ring shapes will be displayed; 3. Add new field ‗index‘ to the two ring shapes (outer = -2, inner = -1) and this is ‗proximity to sea shape file‘; 4. Select the two lakes from land use data and buffer it with 70 m and 140 m. Add new field ‗index‘ ( inner = -1, outer = -2) and this is ‗proximity to lake shape file‘; 5. Union ‗proximity to sea shape file‘ and ‗proximity to lake shape file‘. Convert the result to 100mx100m resolution raster and set raster value = index; 6. Use the raster file together with Layer 4 to calculate the proximity to waterfront raster based on the macro; 7. Select water body from the land use data with grid code = 91, 92, 62. Convert it to 100mx100m resolution raster and set raster value = -1; 8. Combine step 6 and step 7 using ‗mosaic‘ function with ‗minimum‘ option.
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Result:
Sub-layer 6a – Proximity to Waterfront Map
Figure I-53 Proximity to Waterfront Map
Table I-19 The Classification of Layer 6a Sea Breeze Tentative Proximity to Waterfront District Classification Value I High: short distance from coastline (0-70m) -2 with low ground coverage(<=30%) II Medium: short distance from coastline (0- - 1 70m) with medium ground coverage (30%- 50%) or medium distance from coastline (70- 140m) with low ground coverage(<=30%) III Low: long distance from coastline (>140m) or 0 high ground coverage (>50%) or medium distance from coastline (70-140m) with medium ground coverage (30%-50%)
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Layer 6b – Proximity to Open Space
Description: Urban open space, such as park and open area, has a substantial effect on the urban climate and has positive influence on the surroundings (Lo et al., 2003; SDUDB, 2008). The effect allows strong wind penetration into the urban areas producing a long distance air path and resulting in a cooling effect for neighboring areas (Koomena et al., 2007). Open space plays an active role in air quality improvement (Lewis, 1996).
Input Data: Building Volume Map (Layer 1) and Ground Coverage Map (Layer 4).
Methodology: This layer is derived from knowledge-based processing.
Sub-layer 6b shows the proximity to open space map in urban area. An area of a size of 100m x 100m with Building Volume value smaller than 5% and Ground Coverage value smaller than 5% is considered as open space. An open space grid has the potential to benefit its 8 neighbouring 100m x 100m grids. A logical function is established to determine whether a neighborhood grid (n) is a beneficiary. The logical function is as follows: If Layer4(n) = -2 (Ground Coverage <= 30%): beneficiary; If Layer4(n) = -1 (30% < Ground Coverage <= 50% ): beneficiary; If Layer4(n) = 0 (Ground Coverage > 50%): not beneficiary. where Layer4(n) is the pixel value of grid (n). The logical function is implemented as a macro embedded in ArcGIS. Two classification values are assigned (Table I-20).
GIS Operation: 1. Use Building Volume Map and Ground Coverage Map of 100mx100m resolution raster files to define open space (building volume < 5% and Ground Coverage < 5%); 2. Use Ground Coverage 100mx100m resolution raster file to define potentially beneficiary areas (Ground Coverage <= 50%); 3. Use the raster file together with Layer 4 to calculate the ―proximity to openness‖ raster based on the macro; 4. Assign all other pixels classification value = 0.
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Result:
Layer 6b – Proximity to Open Space Map
Figure I-54 Proximity to Open Space Map
Table I-20 The Classification of Layer 6b Proximoty to Open Space Tentative Classification (Benefit from neighborhood open space) Value Yes - 1 No 0
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Layer 6c – Slope Map
Description: The phenomenon of katabatic winds8 is frequently found in long, narrow and steep valleys in mountainous areas (Fernando et al., 2001). Local variations in topography may affect greatly the wind conditions. Colder air generally moves downhill along the valleys. This colder air is beneficial. The down-slope winds are only of local significance, especially for the location at the bottom of the slopes (Lazar & Podesser, 1999). These winds originate from the production of cold air which is a consequence of the negative balance of radiation.
Input Data: DEM data (hk2mgrid) and Layer3.
Methodology: This layer is derived from knowledge-based processing.
Sub-layer 6c shows the slope map of Hong Kong. Steeper topography (>=40%) with greenery has the potential to strengthen air circulation and wind movement around the topography. A logical function is established to determine this benefit. Akin to Layer 3, green space is defined by the NVDI image where NVDI>0.1 (grass and trees). When the greenery data is aggregated to 100m x 100m grid, the conventional threshold of 75% is used to determine whether a grid is green space or not. For a 100m x 100m grid (i), the logical function is as follows: If Slope(i) >= 40% and Green(i) = 1 (green space), for any of its 8 neighborhood grids (n): o If Topo(i) > Topo(n): pixel (n) is a beneficiary of (i). where Slope(i) is the slope value of the grid (i), Green(i) is whether the pixel (i) is green space or not, and Topo(i) is the topographical height of pixel (i), and (n) likewise. The logical function is implemented as a macro embedded in ArcGIS. Two classification values, ―-1‖ and ―0‖ are assigned (Table I-21).
GIS Operation: 1. Use ‗slope‘ function to produce slope map from the DEM data and take the ‗percentage‘ option, the result is 2m resolution; 2. Aggregate the result to 100m resolution, using ―mean‖ option;
8 Katabatic Wind is a high density air flow from a higher elevation mountain down a slope under the force of gravity.
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3. Reclassify: slope >= 40% pixel value is 1; slope < 40% pixel value is 0; 4. Refer to Layer 3, using 75% threshold to generate greenery raster, greenery pixel value is 1, not greenery pixel value is 0; 5. Use the resulted 2 raster files in the previous steps to calculate ―slope‖ raster based on the macro; 6. Assign all other pixels classification value = 0.
Result:
Sub-layer 6c – Slope Map
Figure I-55 Slope Map
Table I-21 The Classification of Layer 6c Proximity to Slope Tentative Classification (Benefit from neighborhood slope areas) Value Yes - 1 No 0
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Conclusion The three sub-layers (Layer 6a, Layer 6b and Layer 6c) can now be combined to form Layer 6 (Proximity to Openness). The rule for the combination is that the Dynamic Potential values will not be calculated redundantly. This is to say that only the maximum value will be selected from one of the three sub-layers to represent the Dynamic Potential value for Layer 6. For example, if Layer 6a obtained the largest Dynamic Potential value, then values for Layer 6b and Layer 6c will be ignored.
GIS Operation: 1. Use ‗Mosaic‘ to add Layer 6a, Layer 6b and Layer 6c , with ―minimum‖ option, and the resulted Layer 6 is in 100m x 100m resolution.
Result:
Layer 6 – Proximity to Openness Map
Layer 6a Layer 6b Layer 6c
Figure I-54 Proximity to Openness Map
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Layer DP – Dynamic Potential Map
By using simple addition of classification values for Layer 4, Layer 5 and Layer 6 at each grid, the resultant classification value is the Dynamical Potential value. Figure I-57b illustrates the Dynamic Potential map.
Input Data: Ground Coverage Map (Layer 4), Natural Landscape Map (Layer 5) and Proximity to Openness Map (Layer 6).
Methodology: This layer is derived from raster-based calculation.
GIS Operation: 1. Use ‗raster calculation‘ to add Layer 4, Layer 5 and Layer 6 and the result is in 100m x 100m resolution.
Dynamic Potential Map
Layer 4 Layer 5 Layer 6
Figure I-57a Components of Thermal Load Map
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Result:
Figure I-57b Dynamic Potential Map of the UC-AnMap
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1.5.3 Wind Information Layer
1.5.3.1 Introduction
Hong Kong is located at the southern coast of China (Figure I-58). Although it is only about 1,100km² in area, 75% of Hong Kong is characterised by mountains (with the highest peak at 957m), alongside an extensive coastline and numerous islands (Chiu & So, 1986). Thus, the wind environment in Hong Kong is complex. .
Figure I-58: Hong Kong’s location and its satellite image
For UC-AnMap, various wind data are considered. This report presents the methodology for understanding the wind data to develop the wind information layer of the UC-AnMap for Hong Kong.
Firstly, the report reviews related studies in Germany and Japan. We aim to understand the methodology and the kind of wind data typically used for UC-Map studies.
Secondly, based on the observed wind data from the Hong Kong Observatory (HKO) stations and the MM5/CALMET model simulations (by researchers of HKUST), the data is coded and mapped on to the GIS based UC-AnMap of Hong Kong providing a spatial understanding suitable for further evaluation. The important wind data for summer months (June-August) of Hong Kong is the main information basis of expert evaluation. Additional information such as the annual wind data of Hong Kong is also collated for background reference. Together with the topographical information, greenery and ground roughness information, the wind data is evaluated and summarised to become the wind information layer of the UC-AnMap.
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1.5.3.2 Objectives
The objectives of the investigation of wind information layers are:
. To desktop review what kind of wind data is typically needed for UC-Map studies, and what kind of wind information are commonly provided; . To collate and code the wind data from HKO stations and MM5/CALMET model simulation into the GIS based UC-AnMap of Hong Kong; . To evaluate, summarise and spatially visualise the prevailing wind directions and patterns in the summer months (Jun-Aug) of Hong Kong; and . To create the wind information layer for the UC-AnMap of Hong Kong.
1.5.3.3 Overview
Pioneering works in Stuttgart, Germany and Tokyo, Japan (Figure I-59) have been reviewed to provide the basis and framework of utilising wind information in this Study.
Figure I-59: Desktop studies on Stuttgart (Germany) and Tokyo (Japan)
Guideline VDI 3787, Part1, Germany
In 1997, Guideline VDI3787 Part1: Environmental meteorology climate and air pollution maps for cities and regions was published as a national standard by the working group of the Urban Climatic Map Committee of Applied Climatology. It aimed to offer expert advices on the methodology of creating UC-Map and also to define the micro-climatic and meso-climatic symbols and representations used in UC-AnMap and UC-ReMap. As
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Germany is the pioneer of UC-Map studies, the Guideline became an international reference for conducting UC-Map studies around the world.
For planning purposes, the Guideline recommends that key wind patterns (wind roses) and the prevailing wind directions be taken into account (Figure I-60). Based on the wind information, the air exchange relationships such as cold and fresh air corridors, and ventilation paths useful for urban planning understanding could be expertly evaluated.
Figure I-60: An example of wind information as in the Guideline VDI 3787, Part1 (The two red boxes highlight the symbols related to wind information)
Cold Air Drainage Area: Nocturnal cold/fresh air production on open sites;
Cold Air Catchment Area: Cold air accumulation in relative depressions, cold air transport tracks;
Stagnant Cold Air, Cold Air Pool: Cold air pool owing to buildings, embankments, forest barrier (not available for Hong Kong).
Downslope winds: Two-dimensional cold air drainage guided by the land relief, i.e.
slopes;
Mountain/Valley Breeze System: Intensive cold air flow directed downward along the
valley (not available for Hong Kong).
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Breezeway / Main Air Path
Wind Rose: The wind data from meteorological stations can be used to represent the
weather observations on the ground. i.e. observed wind direction and frequency on the ground
1.5.3.4 Case Study I-Stuttgart, Germany
Figure I-61: The location of Stuttgart in Germany and its surrounding topography
Stuttgart is an industrial city located in a basin terrain and surrounded by many hills (Figure I-61). According to recent climatic analysis study ("Klimaanalysekarte Stuttgart," 2008) , it is found that 38% of the area in Stuttgart region is poorly ventilated. Due to the surrounding hills, the city suffers from extended periods of weak winds.
Since the 1930s, climatologists, city planners, landscape designers, and architects have worked together to implement a plan to improve the urban wind environment of Stuttgart. Based on an expertly evaluated air flow understanding, the city began to restrict development in some key areas. An open space network system extending from the rural outskirts of the city to its centre was also recognised.
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Wind Statistics The basic wind statistic is the wind rose measured at the observatory stations and used by climatologists of Stuttgart. It gives the frequency of the occurrence of individual wind directions in percentage. Due to the complex terrain, the measured wind directions across Stuttgart are quite different (Figure I-62).
Figure I-62: The measured wind roses in Stuttgartz
The Wind Field Model DIWIMO For understanding of the wind field near the ground, Stuttgart researchers conducted model simulations using the meso-scale diagnostic wind field modeling named DIWIMO (Schaedler & Lohmeyer, 1996). It helped to quantitatively compute the influence of the orthography of
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT individual points9 with a resolution of 250m. The model can produce the air flow pattern maps at near ground level above the urban canopy layer; and the synthetic wind statistics are shown as wind roses of 16 directions (Figure I-63).
(a) (b) Figure I-63: (a) calculation result and (b) synthetic wind roses generated with DIWIMO
Securing the Local Air Exchange
(a) (b) Figure I-64: (a) the evaluated air-flow patterns in Stuttgart, Germany; (b) evaluated preserved areas in Stuttgart for fresh cool air flowing to the city centre (Baumüller et al., 1992b)
9 The orthography of individual points refers to the conversion of 3-D topographic data into 2-D information of individual points on the map. For detailed information, please refer to section 4.3.2 of Climatic Booklet for Urban Development. http://www.staedtebauliche-klimafibel.de/Climate_Booklet/index-4.htm
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Based on the data and study results, climatologists evaluated the air flow pattern in Stuttgart (Figure I-64a). For securing local air exchange, those areas relevant to the ―climatically active surfaces‖10 have been carefully preserved and improved (Figure I-64b) since the 1970s. The whole system of cold air flows consisting of Cold Air Production, Fresh Air Supply, Ventilation and Green Corridors and particularly the “Ventilation Corridors” for transferring fresh air is strictly regulated by planners. One hundred meters is the preferred minimum width for these air flow corridors, which are planted with grass and shrubs.
For instance, based on the wind information understanding, climatologists had identified a potential area for a Ventilation Corridor in Vaihingen some ten years ago, which could enhance air flow. Based on the climatologists‘ advice, the planners defined this area as a Ventilation Zone in the land use plan (Figure I-65a) and the local development plan (Figure I- 65b). The affected areas are demised as green areas under the plans. This area is now covered with vegetation and is beneficial to the exchange of air mass with the neighbouring residential communities (Figure I-66).
(a) (b) Figure IB-65: (a) Ventilation zone as green area in the land use plan; (b) Ventilation zone as green area in the local development plan (Baumüller, 2006)
10 The term of ―climatically active surfaces" refers to both the thermal and the topographical requirements of the local air exchange and also refers to the entire system of cold air production areas and air flow corridors (Baumüller et al., 1992b).
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(a) (b) Figure IB-66: (a) Ventilation zone in an aerial photo; (b) current view of the ventilation corridor in Vaihingen; (Reuter, 2008)
The Stuttgart experience is most applicable to cities with frequent low wind speeds. Other cities in Germany and other countries have since followed Stuttgart‘s approach. By harnessing air flow to ventilate the city, Stuttgart has improved poor air ventilation of the city.
1.5.3.5 Case Study II-Tokyo, Japan
Wind Environment Study Since 1999, Ministry of the Environment (MoE) and Ministry of Land, Infrastructure and Transport and Tourism of Japan Government have worked actively on the study of mitigating the UHI effect. Tokyo Metropolitan‘s 23 wards were chosen to carry out the case study as an example for other cities in Japan. The Eight Local Governments Action Plan (エコウェーブ, 八都県市地球温暖化防止一斉行動) of Tokyo Metropolitan Government has been carried out. In the study, the wind environment of Tokyo Metropolitan Area has been examined and the focus has been on the summer months.
Figure I-67: The location of Tokyo and Tokyo Metropolitan’s 23 wards
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Tokyo Metropolitan is a coastal city located in Tokyo Bay (Figure I-67) and most of its areas are located on the flat Kanto Plain. Only the western part is hilly. So it is evaluated that the wind environment of Tokyo Metropolitan consists mainly of land breeze, sea breeze, valley wind and mountain wind, with the sea breeze being the most dominant.
The wind information for Tokyo Metropolitan Areas In the UHI study of Tokyo (MOE, 2001), other studies on wind conditions were conducted. Firstly, it focused on the local wind analysis based on the wind data from Japan Meteorological Agency. The map of wind roses and prevailing wind directions are considered as the basis for understanding (Figure I-68). Secondly, Japanese researchers conducted ventilation analysis studies at the city level. At the ward level, the major air paths are evaluated based on the terrain information (Figure I-69). Three kinds of wind conditions were evaluated by experts based on an understanding of terrain and land use, including land and sea breezes, mountain and valley wind, and air movements from parks (Table I-22 & Figure I-70). The general descriptions focus on their scales, range, time and directions, and are shown in Table I-22. Table I-22: Three Wind Conditions and Their Characteristics Kind Scale Range Time Direction Wind Speed Effect Early Decrease the Large Metropolitan Morning S to SE ＞5 m/s temp of to Night downtown Sea Breeze Before to Decrease the Land & Sea Medium Ward After SEE ＜5 m/s temp of coastal Breezes Noon area Saitama Mid Moderate the Prefecture to the night to Approximately Land Breeze Medium N to NW condition of north part of Early 2 m/s Nettaiya Tokyo city Morning Night to (no data) Moderate the Mountain Bottom and Medium Early W to NW estimated high temp in Wind hillsides area Morning around 1 m/s night time Mountain Moderate the &Valley (no data) high temp of Wind The outlet areas Valley Wind Medium Daytime E to SE estimated the warm of valley around 1 m/s slopes in day time (no data) Moderate the Downhill air Downwards Small Daytime S to SE estimated > 1 temp rise in Air movements Area m/s day time Movements from Parks Night to (no data) Moderate the Cool air small Neighbourhood Early All estimated 0.1 to condition of Morning 0.3 m/s Nettaiya11 Translated from (八都県市首脳会議環境問題対策委員会幹事会, 2007; 三上岳彦, 2005)
11 Nettaiya: Japanese word to express the Tropical Night when daily minimum temperature equals or exceeds 25 deg.C.
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(a)
(b) Figure I-68 (a) Map of Wind roses at near ground level; (b) Prevailing wind directions (measured by Japan Meteorological Agency in Aug.1998-1999) (MoE of Japan Government, 2003)
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Figure I-69: Example of major air paths in Minato-ku ward, Tokyo (MoE of Japan Government, 2003)
Figure I-70: Evaluated wind information of Tokyo Metropolitan areas (三上岳彦, 2005, 2006)
National Research Project on Kaze-No-Michi (ventilation path) Based on the strategic wind information evaluation, the Ministry of Land, Infrastructure, Transport, and Tourism (the National Institute for Land and Infrastructure Management, the Building Research Institute, and the Geographical Survey Institute ) conducted a detailed 3-
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT year research project starting in 2004 to make the best use of the cool sea breeze (AIJ, 2008). To apply Kaze-no-michi (ventilation path) in urban planning, Japanese researchers classified it into 3 types (Figure I-71) based on the understanding of the sea breeze condition of Tokyo. . Type 1: Kaze-no-michi created by the sea breeze that flows from the coast into the city along the ground surface and along routes such as streets and rivers. . Type 2: Kaze-no-michi that originates from sea breeze aloft. The sea breeze is directed to the earth‘s surface in the city by building complexes along streets and rivers. . Type 3: Kaze-no-michi generated by sea breeze blocked by skyscrapers.
Figure I-71: 3 Types of Kaze-no-michi (ventilation paths) , which brings cool sea breezes into urban areas (AIJ, 2008)
Japanese researchers are continuing their research to implement the study result of Kaze-no- michi in the urban planning system of Japan. For example, incorporating Kaze-no-michi into the UHI Countermeasures and Guidelines (AIJ, 2008).
1.5.3.6 A Summary Of Gerneral Lessons Learnt
Desktop studies of German Guideline [VDI3787 Part1: Environmental meteorology-Climate and air pollution maps for cities and regions] have been conducted. Together with case studies of wind information used in the making of Stuttgart and Tokyo urban climatic and Environmental map, the following key lessons have been learnt:
Wind data is typically collated from observatory data – especially stations in the city. Model simulated data can be used to supplement it.
For planning purposes, the collated wind data is expertly evaluated taking into account topography, land use, water body and greenery understanding of the city and its surrounding areas.
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For urban air ventilation, the background wind, localised land and sea breezes, topography affected channeling and valley winds, cool air production, cool air drainage and downhill air movement, whever applicable are expertly evaluated.
Key wind directions, air circulations and ventilation areas are then coded onto the wind information layer of the Urban Climatic Analysis Map (UC-AnMap).
1.5.3.7 Wind Data For Hong Kong
Based on the desktop studies, the followings are assembled and collated to be expertly evaluated for UC-AnMap of Hong Kong: Wind data from the Observatory Model simulated wind data Topography and landscape/greenery/land use information
HKO Wind Data Hong Kong Observatory (HKO) stations provide a useful and reliable long term data source of the wind environment in Hong Kong (Figure I-72).
Figure I-72: Locations of HKO weather stations
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For this study, a representation of wind data up to 2004 from 40 stations has been assembled and was made available for the study by HKO in July 2005.
The July 2005 dataset was subsequently supplemented with an updated dataset to December 2007 that was made available to the study by HKO in January 2009.
The wind roses have been superimposed onto Hong Kong‘s topographical map. This gives an overall spatial picture of Hong Kong‘s territorial wind environment taking into account the topographical and surrounding land-sea characteristics.
The 1998-2007 dataset has been coded onto the UC-AnMap GIS layers (Table I-25, Figure I- 73 and Figure I-74). An example of the coded data is shown as Figure I-75.
Table I-25: HKO data coded Data Format Raw Data of wind GIS Data of HKO Wind Data Sets Wind Rose speed and direction Wind Rose (.pdf format) (.txt format) (.shp format) Summer (Jun-Aug) √ √ 2004 Annual (Jan-Dec) √ √ Summer (Jun-Aug) √ √ √ Day (11:00am-16:00pm) √ √ 1998-2007 Night (1:00am-6:00am) √ √ Annual (Jan-Dec) √ √ √
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Figure I-73: Summer-July wind roses of HKO stations – with topography background
Figure I-74: Annual wind roses of HKO stations – with topography background
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Figure I-75: An understanding of the territorial wind conditions based on seasonal wind roses of HKO stations – with topography background (1998-2007 Jun-Aug)
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MM5 Wind Data
Mesoscale models like MM5 (Fifth-Generation NCAR/Penn. State Mesoscale Model) are commonly used by meteorologists to predict the wind field based on the regional weather input data. Typically, wind is resolved to 1.5 km x 1.5 km grid resolution over large areas. Scientists at HKUST further resolve this by coupling the prognostic MM5 mesoscale model with the CALMET (California Meteorological Model) diagnostic model for producing high resolution wind fields with resolution of 100m x 100m.
HKUST has a set of MM5/CALMET model simulated data for Hong Kong of the year 2004. The observed horizontal wind from HKO have been used to nudge into the governing equations for analysis nudging, and cross checking work has been conducted to ensure quality (Yim et al., 2007; 2009) (see details in Appendix 6 and Appendix 7). The MM5/CALMET intranet website at HKUST reports wind roses and wind frequency tables of 30m, 60m, 120m, 230m and 450m. According to the building height information from PlanD, it could be found that the mean building height of HK is around 60m above the ground, which could be used to define the height of urban canopy layer of HK. The MM5 data at 60m is more appropriate to be used in this study. Thus, the MM5 data at 60m is selected for the wind evaluation. An example of the wind rose diagram of MM5/CALMET data is shown in Figure I-76. Wind data as summarised in Table I-26 has been extracted and referenced for this study. A prevailing summer wind direction map is in Figure I-77 and an example of the coded MM5 data (at 60m) is in Figure I-78.
Table I-26: MM5 Data sets Data Format MM5 Wind Data Sets Wind Rose Wind speed and predominant (hourly data & daily data) in .pdf in .shp wind direction in .shp Summer (Jul-Aug) √ √ √ Day(11:00am-16:00pm) √ √ √ 2004 Night(1:00am-6:00am) √ √ √ Annual (Jan-Dec) √ √ √
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Figure I-76: An example of wind roses (MM5/CALMET simulation) provided by HKUST
Figure I-77: Prevailing summer (2004 Jun-Aug) wind directions based on MM5/CALMET simulation – with topography background
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Figure I-78: An understanding of the territorial wind conditions based on summer wind roses of MM5 simulation – with topography background (2004 Jun-Aug)
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1.5.3.8 Issues & Considerations
In line with international practice, especially the experience gained by researchers in Germany and in Japan, for UC-AnMap studies, the collected information are expertly evaluated based on an understanding of the:
Background wind, Localised land and sea breezes, Topographically influenced (channeling) winds, Topographically influenced (downhill (katabatic)) air movements
Background Wind
Hong Kong is on the southeast coast of the Asiatic continent. Figure I-79 shows an understanding of the Monsoon circulation in January and in July.
winter condition (Jan) summer condition (Jul) Figure I-79: An understanding of Monsoon circulations in eastern and southern Asia (Trewartha, 1967)
A seasonal understanding of wind in Hong Kong has been summarised (Tam, 1987; Yan, 2007) (Figure I-80).
. In winter, referred to as the period from mid-October to early April, background winds are persistently between the north and the east.
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. Spring starts in mid-April and lasts till mid-May when northerly winds become infrequent. The prevailing wind direction is mainly between the east and the northeast. . In summer, the prevailing wind comes from the southwest and the background winds occur with much higher frequency between the west and the south. . By autumn, from mid-September to mid-October, the northerly winds return. The background winds are mainly between the north and the east.
Figure I-80: Seasonal mean wind directions (Yan, 2007)
Among all the HKO Weather Stations, Waglan Island station (WGL) is normally regarded as the reference station to capture the background wind condition by wind engineers (Figure I-81). It is located on a small island southeast of Hong Kong and less affected by urban structure, buildings or topography. Lam (2006) has found that there was no significant long- term trend in the wind speed at WGL. Based on the WGL wind roses, the annual prevailing wind in Hong Kong is from the northeast quadrant. The summer prevailing wind is from the south-west (Table I-27). The key wind environment of Hong Kong is the main wind conditions in the summer months, when the background wind at WGL is mainly from the south quadrant. According to their homogeneous or similar prevailing wind directions, the
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Figure I-81: Wind roses of WGL (Annual and Summer)
Waglan Island Prevailing Season Month Mean Wind Direction Speed (km/h) (deg.) January 070 25.4 Winter February 070 25.1 March 070 23.5 Spring April 070 21.2 May 080 20.2 June 230 23.3 Summer July 230 21.9 August 240 20.0 September 090 22.8 Autumn October 080 28.7 November 080 27.9 Winter December 070 26.5 Annual 070 23.9
Table I-27: Monthly Prevailing Wind Direction and Mean Wind Speed Recorded at the Observatory and Waglan Island between 1971 and 200012
It can be concluded that the summer background synoptic wind of Hong Kong is from the South- West. It is also in general weaker than the winter winds.
Localised Land and Sea Breezes
Figure I-82: An understanding of the daily mechanism of Land and Sea breezes. Note the common onset time of the sea breezes at just before noon (Simpson, 1994)
12 From: http://www.hko.hk/cis/normal/1971_2000/normals_e.htm#table7
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The basic sciences of land and sea breezes is well documented (Simpson, 1994) (Figure I-82). Land and Sea Breezes are thermally induced local circulation found in coastal regions (Oke, 1987; Wallace & Hobbs, 2005) (Figure I-83). They are driven by the different heating rates over the sea and the land, and occur most observably when the prevailing background wind is weak (Zhang & Zhang, 1997).
Day time Night time Figure I-83: An understanding of the Land and Sea Breezes13
Researchers have identified two scales of sea circulations. At the larger scale, sea breezes can have a thickness of 1 to 2 kilometers vertically (Figure I-84). Oke summarises, ―Commonly the sea breeze blows at 2-5 m/s, extends inland as far as 30 km, and affects the air flow up to a height of 1 to 2 km …‖ (Oke, 1987, p.169).
For undulating coastlines, more localised land-sea air circulations can be observed (Figure I- 84). They are normally smaller in scale and height (around 50-200m), do not penetrate too far inland, and are weaker and more turbulent. However, Oke noted, ―inhabitants of coastal settlements often find the cool sea breeze to be beneficial in offsetting a hot climate‖ (Oke, 1987, p.170).
(a) (b) Figure I-84: Two scales of sea breezes (a) the localised sea breezes that mainly flow perpendicular to the coastline; (b) the meso- scale sea breeze understanding of Tokyo Bay(浅井富雄，1996)
13 From: http://ess.geology.ufl.edu/ess/Notes/AtmosphericCirculation/daynight_lg.jpeg
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Hong Kong is a coastal city, and land and sea breezes can be observed. This is well demonstrated with studies by Dr Yeung (Figures I-85, 86 and 87); and by Prof Fung (Figure I-88).
at 8:00am at 14:00pm Figure I-85: Dominant wind direction observed at surface anemometer stations (Yeung, 1991)
at 8:00am at 14:00pm Figure I-86: Sea breeze simulation for 10 Dec 1990 (wind at 10m above terrain) (Yeung, 1991)
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Figure I-87: An expert understanding of the sea breezes at the western territory of Hong Kong on 17 Nov 2007 under weak background wind, after K K Yeung, 2007.
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Figure I-88: 24 hourly variation of wind field simulated by MM5-CALMET model on 28 Sep.2004, provided by Prof. Jimmy Fung of HKUST
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Based on HKO‘s 1997-2006 data, CUHK researchers have conducted a study on the differentials between WGL data and other HKO wind station data, and have concluded that weak background wind conditions are responsible for noticeable localised sea breezes vs. background wind at the stations shown in orange in Figure I-89, whereas at stations shown in blue, the differentials are not that noticeable. The study coincides with the results of other researchers.
(a) (b) Figure I-89: HKO stations and Land-Sea Breeze Effect in HK. (a) (Orange) dots show the HKO station studied that is notably affected by sea breezes. (Blue) dots show the HKO station studied that is not noticeably affected by sea breezes; (b) shows Ching Park House（CPH） wind directions under weak background (WGL) wind conditions. The larger differential between CPH and WGL wind directions in the afternoon can be attributed to the effects of sea breezes.
Based on the statistical analysis of meteorological data, Zhang and Zhang (1997) show that sea breeze occurs on an average of 69 days per year and at around 2m/s to 5m/s in Hong Kong. It is found that usually the sea breezes start between 10:00 and 11:00 am, reaching their maximum speeds between 13:00 and 15:00 pm, and then gradually subsiding between 15:00 and 20:00pm, after which it is replaced by the weaker land breezes at night. During the night, land cools quickly, flow of air returns from land to sea. Their understanding of the pattern and directions of the land and sea breezes is summarised in Appendix 5. For Hong Kong, the sea breeze generally influences more areas than land breezes.
Taking into account the effects of sea breezes in the afternoon of the summer months of Hong Kong, HKO summer daytime data is coded and visualised. Two examples are shown in Figure I-90 and 91.
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Figure I-90: Wind roses of HKO stations – with topography background (1998-2007, summer day time: 11:00am-16:00pm)
Figure I-91: Wind roses of HKO stations – with topography background (1998-2007, summer night time: 01:00am-06:00am)
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Topography Influenced (Channeling) Wind
The topography of Hong Kong is characterised by extensive mountain coverage (with the highest peak of 957m) (Figure I-92) (Chiu & So, 1986). For an understanding of the general (territorial) wind patterns and directions as affected by the topography, the issues on channeling wind and valley wind are examined.
Figure I-92: Topography map of Hong Kong
Channeling The channeling wind indicates that at the regional or territorial level, the winds approaching a broad valley will be forced to flow along the valley. Based on an understanding of the topographical conditions at the regional level of Hong Kong, it is evaluated that there are three main channeling valleys that affect the urban areas (Figure I-93). The summer wind roses of HKO‘s Sha Tin, Tuen Mun, Tsim Sha Tsui stations illustrate the channeling effects (Figures I-94 to 96):
1) the area along Tuen Mun River Channel from Tuen Mun to Lam Tei and Hung Shui Kui;
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2) the area along Shing Mun River Channel from Shatin to Tai Wai; and 3) the seafront area of Victoria Harbour and the Kai Tak old airport areas.
1 2
3
Figure I-93: Three observed channeling affecting areas in Hong Kong (including the Kai Tak old airport areas) shown within the red circles
Figure I-94: Summer wind rose of HKO Sha Tin station
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Figure I-95: Summer wind rose of HKO Tuen Mun station
Figure I-96: Summer wind rose of HKO Star Ferry (Tsim Sha Tsui) station
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Shielding
Detailed theoretical, numerical and experimental understanding from studies of wind flows over hills have been well documented (Jackson and Hunt, 1975; Mickle et al., 1988; Ross et al., 2004; Bitsuamlak et al., 2004; Tamura, 2007; Yim et al., 2007; Loureiro, 2009). This knowledge base is important for wind engineers working on site wind availability, as well as detailed design of buildings near hills. Urban climatologists typically generalise the understanding to evaluate the shielding effects to the urban areas (Xu and Taylor, 1995); it goes hand in hand with the evaluation on ―channeling‖ effect. With an understanding of the shielding and channeling effects of hills, the changes of the prevailing wind directions of an area could be evaluated.
Professor Lutz Katzschner has considered that 4 hill ranges are important when the wind information of HKO and MM5/CALMET are later evaluated (Figure I-97).
Figure I-97: Four main topographical barriers near urban areas and another one on Lantau Island identified
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Topographically Influenced (Downhill (Katabatic)) Air Movement
For UC-AnMap studies, the usefulness of the cool air production areas (forested, vegetated and unpaved areas), and their outflow to benefit the surrounding areas can be noted (Figure I- 98)
Figure I-98: Cool air and outflow analysis map of Berlin Climate Map
Hong Kong has a hilly topography. As established through international research, vegetated hill slopes next to urban areas are known to bring in cool downhill air movement to relief the warmer urban areas (Oke, 1987; Barlag & Kuttler, 1990/91; Hupfer & Kuttler, 1998; Weber & Kuttler, 2003). Using satellite imaging for Tuen Mun, Professor Nichol has noted the cooling effect of urban areas next to nearby vegetated slopes (Figure I-99) (Nichol, 2005).
(a) (b) (c) Figure I-99: The cooling effect of the vegetated hillsides of Tuen Mun Areas (a) Tuen Mun Areas (Google Image); (b) Surface Temperature from ASTER scene-corrected image at 21:40 pm, 06 Oct 2001 (Nichol, 2005); (c) The down slope air movement according to expert evaluation
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Researches have indicted that the thickness and the air velocity of the downhill movement depends on a number of parameter, as in equation 1. Bergen (1969) has established that the velocity of the down slope air movement depends on the temperature difference, the angle of the slope and the distance the air travels (the length of the slope) (Figure I-100). Other researches also have similar findings (Yoshino, 1984; McNider, 1984; Kondo and Sato, 1988). ½ ⅔ ½ Um (Δθ ) , Δθ∝R0 , Um/(γ ) x, (1) where
Um is the average air movement velocity, Δθ the potential temperature drop down the slope,
γ the sine of the angle of the slope to the horizontal along the streamline, x the downslope distance from the virtual origin of the flow measured along the streamline, and
R0 the average net radiation loss on the slope.
Figure I-100: [Left] the profile far left is an understanding of the velocity profile of the katabatic air movement; [right] possible velocities of downhill air movement
There is no known field measurement in Hong Kong that has estimated the strength and characteristics of the downhill air movement of slopes next to urban areas. Based on literature review, prudently, for a vegetated slope at an angle of 5 to 15 degrees, a slope length of a few hundred metres, and a temperature difference of 1-3 ○C, a down slope air movement of around 0.5 to 1 m/s can be expected (Stull, 988; Horst and Doran, 1986) (Figure I-100). The thickness of this gravity flow is not high, around 5 to 20m. Such a flow can easily be dissipated by intercepting building structures and warmer paved surfaces (Barlag & Kuttler, 1990/91; Hupfer & Kuttler, 1998; Weber & Kuttler, 2003). It is not anticipated that the flow can extend more than one building block from the bottom edge of the vegetated hill.
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1.5.3.9 Expert Evaluation
Figure I-101: An expert evaluation of the annual wind information by Dr K K Yeung of HKO (The prevailing wind directions can be noted. The channeling effects of the Victoria harbour, as well as in Shatin and in Tuen Mun are apparent. )
Figure I-102: An early and initial expert evaluation of shielding and channeling effects by Professor Lutz Katzschner (2006)
Expert evaluation of the territorial wind information can be conducted using wind roses of measurement stations (Figure I-101). Professor Lutz Katzschner has also expertly evaluated the topography of Hong Kong in terms of shielding and channeling (Figure I-102). Referring
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT to the meteorological wind data of HKO stations, he has also remarked on their key characteristics. He has attempted to understand the wind information characteristics that are captured by the respective stations.
In Hong Kong, according to HKO‘s previous studies and suggestions, there is only one station, namely Waglan Island Station (WGL) used as rural station to capture the background wind condition, as it is largely unaffected by urban structure, buildings and topography. For a better urban climatic understanding, it is important to have more detailed wind information for the UC-Maps. Wind at WGL is mainly from the south quadrant in summer months. According to their homogeneous or similar prevailing wind directions, key wind environments could be defined based on the expert evaluation of meteorological wind data, simulated MM5 data and topographical information.
The wind information layer gives a generic wind information understanding for the territory of Hong Kong and provides useful results and understanding e.g. summer prevailing wind directions, the availability of sea breeze, downhill air movements and breezeway for the site.
According to international experience on the presentation of wind arrows or wind regions, it is noted that the arrows only symbolise different winds, and are not relative to the intensity of wind speed or penetration power; the boundaries of the wind regions should also not be treated as being definitive. Expert opinions on the detailed and specific information on the boundaries of different wind regions could be sought if needed. In a nutshell, wind arrows of the wind information layer indicate the prevailing wind directions of the area whereas the wind regions further characterise them to include the quadrant of the key wind directions. The information side by side shows the wind characteristics of the area.
In line with international practice as explained in the desktop study section of this report, the collected information is evaluated. For the UC-AnMap, the evaluation has identified the prevailing wind direction of various climatic zones, as well as a brief description of their key characteristics. This information, when overlaid onto the Thermal Load and Dynamic Potential information of the UC-AnMap, allows the urban morphology to be further understood and for planning recommendations to be formulated with regards to the prevailing and critical air ventilation of an urban area.
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1.5.3.10 Layer 7 - Wind Information Layer － Prevailing Wind Directions (Summer)
For the UC-AnMap of Hong Kong, we focused on the summer months (Jun-Aug) – the annual wind has also been examined for reference. The outcome of the evaluation of wind information for summer, the Wind Information Layer, is illustrated as Figure I-103. The symbols are shown as Table I-28. As explained earlier, the 4 key considerations have been factored in:
(A) Background wind, (B) Localised land and sea breezes, (C1) Topographically influenced (channeling) winds, and (C2) Topographically influenced (downhill (katabatic)) air movements
(A) and (C1) are to be considered together as they are related to the background wind and the effects of topography. (B) is localised and is time dependent. This study assumes an afternoon condition when the sea breezes are more important to consider. (C2) is also localised and is related to the topography, vegetation, and the cool air production areas of the slopes.
The definition of the boundaries of different wind regions is mainly based on expert evaluation of the territorial wind information and topography information. Different wind regions are shown in different colours in the wind information layer and denoted as C1, C2, C3, C4, D, V, SE, E and S. In each wind region, there are one or two big black wind arrows, which show the key wind directions. For the area of sea breeze and downhill air movements, only those beneficial for urban areas are presented.
. SE, E and S According to the collected wind data, it could be found that the summer prevailing wind directions are mainly from a particular quadrant due to the topographical characteristic. So, the areas with winds mainly from the southeasterly quadrant are defined as SE areas; the areas with winds mainly from the easterly quadrant are defined as E areas; and the areas with winds mainly from the southerly quadrant are defined as S areas. The shielding effects and channeling effects are taken into account to define the wind regions, e.g. the boundaries between Area SE and Area S on Lantau Island, the boundaries between Area D and Area S on Hong Kong Island.
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. C1, C2, C3 and C4 Since the wind condition of the urban areas around Victoria Harbour and on Kowloon Peninsular is much more complex than other areas, experts decided to give more detail evaluation and to define the wind information of these areas as different city climates according to the meteorological wind data, MM5 simulated wind data, and the understanding of field measurement results in Tsim Sha Tsui East and Tsuen Wan areas. Thus, the whole Kowloon peninsular are divided into 3 city climate regions (Area C1, C2 & C3) with different climatic planning recommendations and also the north shore of Hong Kong Island are defined as Area C4.
. D The areas of the northern hillside of Hong Kong Island is very sensitive to its surrounding areas, especially the north shore of Hong Kong Island. As both of the downhill air movements and summer prevailing wind come from the southerly quadrant, this area with important downhill air movements for Hong Kong Island is defined as Area D. Experts suggested this area be highlighted so that more attention can be given in future planning and development to protect the downhill air movements, which could be beneficial to the leeward urban areas, such as the highly built-up areas of Sai Ying Pun, Sheung Wan, and Wan Chai.
. V In Hong Kong, due to the hilly topographical condition and existing river channel systems, 3 main channeling valleys formed by their local terrain can be found in Tuen Mun River Channel (from Tuen Mun to Lam Tei and Hung Shui Kui), Shing Mun River Channel (from Shatin to Tai Wai) and the seafront areas of Victoria Harbour and the Kai Tak old airport areas. The wind condition of these 3 main channeling valleys normally is affected by their surrounding terrain and the wind direction can be observed in both directions flowed along their central axis. Experts suggested areas of these 3 main channeling valleys should be highlighted so that more attention can be given in future planning and development to respect the channeling effect, which could be beneficial to the surrounding waterfront/seafront urban areas, such as highly built-up areas of Kowloon peninsula, Tuen Mun, Shatin and Tai Wai.
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Figure I-103: Wind Information Layer－ Prevailing Wind Directions (Summer)
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Table I-28: Wind information and symbols Regional Wind Pattern Name Type Symbols Key Wind Directions (summer months most frequent wind direction of the areas)
Channeling Wind in Both Directions Wind Arrows Sea Breeze
Downhill Air Movements for Urban Areas
C1 – City climate, SW ventilated
C2 – City climate of inland area, weakly ventilated
C3 – City climate, SE ventilated
C4 – City climate, various ventilation systems
D – Area with important downhill air movements for HK Wind Regions Island
V – Main air ventilated channels
SE – Areas with winds from the southeasterly quadrant
E – Areas with winds from the easterly quadrant
S – Areas with winds from the southerly quadrant
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1.5.3.11 Limitations
The data collation, assembly and codification, and the expert evaluation employed in this study follow a similar methodology to that of the German experience. Various wind data is simplified for working on urban climatic planning recommendations.
The study relies on data from existing HKO stations. Additional intra-urban observation stations would assist a better understanding of the more localised wind environment, like the land and sea breezes, and downhill air movements. Currently, only 2004 MM5/CALMET is available to the study team. A multi-year (say 3-5 years) dataset would be more representative.
The wind information layer is part of the UC-AnMap and should not be used for any other purposes, such as site-specific AVA studies, as it only gives a generic understanding of the wind environment in different parts of Hong Kong.
1.5.4 Steps of creating the UC-AnMap
The methodology of collating various layers of information for the UC-AnMap based on the understanding of Thermal Load and Dynamic Potential largely follows the experiences of Kassel, Stuttgart and Freiburg UC-Maps in Germany. Whilst the layers‘ own classifications are based on the parameter‘s impact on the PET value, the eventual UC-AnMap (based on the Thermal Load and Dynamic Potential layers) is synergetic and knowledge based in nature.
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Buildings Landuse Topography
Building Volume Topography Green Space Ground Coverage Natural Landscape Proximity to Openness
+
Thermal Load Dynamic Potential
UC-AnMap Wind Information Final UC-AnMap
+ =
Figure I-104 The structure of the 6 Layers for creating the UC-AnMap (100m x 100m raster based)
Figure I-105 Work steps for creating the UC-AnMap (Graphics used are indicative)
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The procedures of making the UC-AnMap are:
Step 1 Layer 1, Layer 2 and Layer 3 with pixel values at 100m x 100m grid are synergised through the function of raster calculation in GIS to become the Thermal Load map. This results in 10 classes from -4 to +5.
Step 2 Layer 4, Layer 5, Layer 6a, Layer 6b and Layer 6c with pixel values at 100mx 100m grid are synergised through the function of raster calculation in GIS to become the Dynamic Potential map. This results in 6 classes from -5 to 0.
Step 3 The Thermal Load and Dynamic Potential pixel values at 100m x 100m grid are synergised through the function of raster calculation in GIS. This results in 14 classes from -8 to +5.
Step 4 For the purpose of planning information needs, the 14 classes are simplified and collated, based on knowledge interpretation, into 8 classifications.
The characteristics of the 8 classifications are assigned based on knowledge interpretation of their likely impact on urban thermal comfort typical of Hong Kong summer conditions (Ta =28 ○C), from Moderately Cooling to Very Strong Warming (Table I-29). The PET interval between each classification is in the order of about 1 ○C. Typically, the practice is that the more critical mid-range values are kept whilst the two extreme ends are compressed. Class 3 (low Thermal Load and good Dynamic Potential) is evaluated to be neutral; hence Classes 1 and 2 are on the cooling side, and Classes 4 to 8 are on the warming side.
Table I-29 An understanding of the characteristics of the 8 classifications Impact on Thermal Urban Climatic Class Comfort
1 Moderately negative Thermal Load and ●● Moderate Good Dynamic Potential cooling 2 Slightly negative Thermal Load and Good Dynamic Potential ● Slight cooling
3 Low Thermal Load and Good Dynamic Potential - Neutral
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Some Thermal Load and Some Dynamic 4 ● Slight warming Potential
Moderate Thermal Load and Some ●● Moderate 5 Dynamic Potential warming ●●● Moderately Moderately High Thermal Load and Low 6 strong Dynamic Potential warming High Thermal Load and Low Dynamic ●●●● Strong 7 Potential warming
Very High Thermal Load and ●●●●● Very strong 8 Low Dynamic Potential warming The colour dots: ● denotes cooling and ● denotes warming. 1 moderately negative Thermal Load due to higher altitude and adiabatic cooling, and greenery and trans-evaporative cooling 2 slightly negative Thermal Load due to greenery and trans-evaporative cooling 3 to 8 various classes of warming impact due to increasing Thermal Load and decreasing Dynamic Potential
Impact on thermal comfort is evaluated and categorised using PET based on the intra-urban temperature differences due to Thermal Load and Dynamic Potential. Typically, from moderate cooling to neutral, the PET value differences are roughly 2 to 3 ºC ; from neutral to very strong warming, the PET value increases are approximately 3 to 5 ºC . All PET values quoted here assume conditions under shade in the summer month conditions of Hong Kong.
Step 5 Field measurements have been conducted to calibrate and verify the classifications. For example, if an area is of a ―Class 3 - neutral‖ condition and the corresponding PET is 28 ºC , then the PET of ―Class 7 - Strong Warming‖ could be estimated to be at most 4 ºC higher which is at 32 ºC . The higher PET in this case is mainly due to the relatively high Thermal Load and low Dynamic Potential of the area.
The field measurements also verify that the pixel pattern of the UC-AnMap and the results of the field measurements are in good agreement. Field measurements are presented in details in Section 1.8.
1.5.5 The UC-AnMap The Thermal Load and the Dynamic Potential layers (Figure I-106a) are evaluated and combined. The UC-AnMap of Hong Kong with 8 climatic classes has resulted (Figure I- 106b). As the main objective of the map is to describe and evaluate thermal comfort, PET is
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Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT used as a synergising index. The classification follows the thermal sensation based on the heat balance equation under steady conditions (Table I-30).
Input Data: Thermal Load Map Dynamic Potential Map
Methodology: This map uses raster-based calculation and reclassification.
GIS Operation: 1. Use ‗raster calculation‘ to add the ―Thermal Load Map‖ and the ―Dynamic Potential Map‖(Figure I-106a), the resultant map is 100mx100m resolution with 14 classification values; 2. Use ‗group value‘ function to group the 14 values into 8 classes (Figure I-106b).
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Result:
Urban Climatic Analysis Map for Hong Kong 100 x 100m resolution, raster based, without wind information
Thermal Load Map
Dynamic Potential Map
Figure I-106a Components of Urban Climatic Analysis Map combining Thermal Load Map and Dynamic Potential Map
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Figure I-106b The UC-AnMap (Classification at Table IB-28), 100 x 100m raster based, without wind information
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1.6 FINAL UC-ANMAP The wind information is incorporated into the final UC-AnMap. Air paths, air mass exchange and air circulation are considered. The Final UC-AnMap comprises 8 urban climatic classes as listed below.
Table I-30 Eight Classifications of the UC-AnMap Approximate PET Impact on Thermal Class Urban Climatic Class Difference Comfort 1 Moderately negative Thermal Load -2 Moderate Cooling and Good Dynamic Potential 2 Slightly negative Thermal Load and -1 Slight Cooling Good Dynamic Potential 3 Low Thermal Load and Good 0 Neutral Dynamic Potential Some Thermal Load and Some 4 +1 Slight Warming Dynamic Potential Moderate Thermal Load and Some 5 +2 Moderate Warming Dynamic Potential Moderately High Thermal Load and Moderately strong 6 +3 Low Dynamic Potential Warming High Thermal Load and Low 7 +4 Strong Warming Dynamic Potential Very High Thermal Load and Low 8 +5 Very strong Warming Dynamic Potential Note: 1 moderately negative Thermal Load due to higher altitude and adiabatic cooling, and greenery and trans- evaporative cooling 2 slightly negative Thermal Load due to vegetated slope and trans-evaporative cooling 3 to 8 various classes of warming impact due to increasing Thermal Load and decreasing Dynamic Potentials
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Figure I-107 The UC-AnMap (Classification at Table IB-28) of Hong Kong with Wind Information Layer - Prevailing Wind Directions (Summer) 1.7 DESCRIPTIONS OF THE UC-ANMAP The 8 urban climatic classes are explained below:
Moderately Negative Thermal Load and Good Dynamic Potential (Class 1) These areas are situated on the higher altitudes of mountains and steep vegetated slopes. Adiabatic cooling 14 and trans-evaporative cooling are prevalent to bring about good dynamic potential and moderately negative thermal load. As a result, the temperature is usually very cool. These areas are sources of cool and downhill wind. This urban climatic class includes the summits of various mountains and peaks, e.g. Victoria Peak, Kowloon peaks, Tai Mo Shan, Pat Sin Leng, Lantau Peak, etc.
Slightly Negative Thermal Load and Good Dynamic Potential (Class 2) These areas are extensively covered by natural vegetation, greenery, including the hilly slopes and natural coastal areas. Trans-evaporative cooling is prevalent to bring about good dynamic potential and slightly negative thermal load. As a result, the temperature is generally cooler. These areas are sources of cool and fresh air. This urban climatic class includes many country park areas, beaches and outlying islands e.g. Plover Cove, Clear Water Bay, Po Toi, etc.
Low Thermal Load and Good Dynamic Potential (Class 3) These areas usually consist of more spaced out development with smaller ground coverage and more open areas, and situated very close to the sea. As a result, the temperature is mild. This urban climatic class includes some undeveloped coastal urban areas and many low- density developments in the urban fringe areas or sub-urban outskirts e.g. Mui Wo, Shek O, Tseung Kwan O South, Pak Shek Kok Science Park, etc.
Some Thermal Load and Some Dynamic Potential (Class 4) These areas usually consist of low to medium building volumes in a developed yet more open setting, e.g. in the sloping areas with a fair amount of open space between buildings. As a result, the temperature is slightly warm. This urban climatic class includes areas such as Mid-Levels on Hong Kong Island, Upper Happy Valley, Chinese University of Hong Kong, and other hillside development areas, etc.
Moderate Thermal Load and Some Dynamic Potential (Class 5)
14 Adiabatic Cooling involves no heat gained or lost during the process of air cooling. For example, a rising air parcel expands and cools as the atmospheric pressure decreases upward
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These areas usually consist of medium building volumes situated in low-lying areas further inland from the sea or in areas fairly sheltered by natural topography. As a result, the temperature is warm. This urban climatic class includes many medium density developed urban areas with urban greenery, e.g. Discovery Bay, Fairview Park in Yuen Long, Hong Lok Yuen in Tai Po, etc.
Moderately High Thermal Load and Low Dynamic Potential (Class 6) These areas usually consist of medium to high building volumes located in low-lying development areas with relatively less urban greenery. As a result, the temperature is very Map showing areas with predominantly warm. This urban climatic class includes e.g. the peripheral of the main urban area and class 5 to class 6 climatic zones many development areas of new towns.
High Thermal Load and Low Dynamic Potential (Class 7) These areas usually consist of high building volumes located in low-lying well-developed areas with few open areas. As a result, the temperature is generally hot in these areas. Most of the developed parts of the main urban areas in Kowloon and north shore of Hong Kong Island and core development areas of the new towns are typical of this urban climatic class.
Very High Thermal Load and Low Dynamic Potential (Class 8) These areas usually consist of very high and compact building volumes with very limited open areas and permeability due to shielding by buildings. Full and large ground coverage is Map showing areas with predominantly prevalent and air paths are restricted from the nearby sea or hills. As a result, the temperature class 7 to class 8 climatic zones is very hot in these areas. This urban climatic class includes some highly developed core areas, e.g. Tsim Sha Tsui, Yau Ma Tei, Mong Kok, Lai Chi Kok, Sheung Wan, Central, Wan Chai, Causeway Bay, North Point, etc.
1.8 CALIBRATION AND VERIFICATON OF THE UC-ANMAP Different climatic factors work synergistically to determine the urban climate of Hong Kong. The analysis of various climatic factors in each layer of the UC-AnMap provides basic understanding of the relationship between urban environment and urban climate of Hong Kong and forms the basis of the classification of the UC-AnMap. This classification is further calibrated with consideration of Hong Kong‘s unique urban microclimatic characteristics.
Two case studies of on field measurements are conducted in Tsim Sha Tsui and Tsuen Wan (Figure I-108) respectively. The result of Tsim Sha Tsui measurement provides useful data to be referenced for calibrating the classification of the UC-AnMap for Hong Kong (Figure I- 109). The results of Tsuen Wan measurement are compared against the UC-AnMap (Figure I-
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110) and as shown in Figure I-111, it demonstrates that the classification of the UC-AnMap and the field measurement results are in good agreement.
TTsssuueenn WWaann
TTsssiiimm SShhaa TTsssuuiii
Figure I-108 Spot measurement in Tsim Sha Tsui and Tsuen Wan
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Figure I-109 The Map of PET Pattern compared with UC-Map for Field Measurement on Tsim Sha Tsui on 19 Sep 2006
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Figure I-110 The Map of PET data compared with UC-Map for Field Measurement on Tsuen Wan site on 15 May 2008 An example of the relationship between PET values calculated from the field measurement‘s results and the classes of the UC-AnMap in Tsuen Wan Areas is plotted to find their linear trend (Figure I-111). It can be found that 1 level difference in UC-Map Class equals to 1 degree of PET value and the relationship is strong (R2≈0.74). That means the classification of UC-AnMap and the predicted human comfort pattern in UC-AnMap are reasonable and in good agreement with the real climatic condition on site.
Figure I-111 The relationship between PET and the classes of UC-An Map based on the result of spot field measurement in Tsuen Wan areas on 15 May 2008
1.9 UPDATING OF UC-ANMAP
The first version of the UC-AnMap for Hong Kong was developed in GIS based on the 2006 version of buildings, land use and topography data. Since all layers and UC-AnMaps are developed and managed in GIS, and UC-AnMaps are created in layers, it is easy to update the layers by incorporating any new developments via GIS, especially for Layer 1 and Layer 4 which are based on the buildings data. Thus, having obtaining the 2009 version of buildings data, the second version of UC-AnMap for Hong Kong has been developed.
Building geometry, urban morphology Land use layer, building shapefile, podium shapefile, DEM raster files could be updated every 5-6 years. Once they are updated, the UC-AnMap can be re-generated.
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Scientific development Additional climatic information will become available. In addition, from time to time, there will be new scientific understanding and/or new technology allowing a better map to be created. On the whole, scientific updating could for instance be done every ten years.
Differences between 2006 version and 2009 version of UC-AnMap Urban Climatic Analysis Map for Hong Kong 100m x 100m resolution, raster based, without wind information
2006 Version 2009 Version
Figure I-112 The differences between 2006 version and 2009 version of UC-AnMap The differences between 2006 version and 2009 version of UC-AnMap could be observed from Figure I-112. The analyses on comparison are:
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(i) Because of the new building data set (2009 version), the areas with increasing value of urban climatic classes are mainly observed in the northern part of New Territories, such as Tuen Mun, Yuen Long, Shap Pat Heung, and Hong Kong Airport etc. (ii) Since the new greenery data (NVDI) with more precise vegetation information is incorporated into Layer 3, Layer 5 and Layer 6, the values of major greenery areas are decreased by 1 to 3 classes. For example, in 2009 version, the urban climatic class identified for CUHK is more appropriate, since there are lots of trees on campus as presented by new greenery data (NVDI). (iii) New logic functions are employed into Layer 6 (refer to its detail description and methodology part), so the values of areas covered by vegetation are decreased.
1.10 UC-ANMAP IN GIS FORMAT
Since the UC-AnMap is mainly created, manipulated and stored in the software of ArcGIS containing all separate layer files, they could not be included in this paper report. Therefore, all data files for UC-AnMap have been submitted in a separate CD.
1.11 FUTURE WORK
Refinement and adjustment of the UC-AnMap can be further made according to new expert knowledge obtained. Based on the final UC-AnMap, the UC-ReMap can be prepared. This will be explained in Part I(C).
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PART I(C): URBAN CLIMATIC PLANNING RECOMMENDATION MAP FOR HONG KONG
PART I(C)-1 INTRODUCTION
1.1 INTRODUCTION
There is a vision to design a sustainable, healthy, and comfortable city for its inhabitants. To achieve that, it is necessary to factor the urban climatic considerations holistically and strategically into the planning process.
The Urban Climatic Planning Recommendation Map (UC-ReMap) is planning oriented. Based on the information and analysis obtained from the Urban Climatic Analysis Map (UC- AnMap), UC-ReMap and planning recommendations from the urban climatic point of view can be formulated. Accordingly, the valuable areas, the problem areas, climatically sensitive areas and air paths can be identified spatially.
Firstly, the report reviews related studies of UC-ReMap in Germany and Japan so as to draw lessons and understand the best practices in forming a methodology of UC-ReMap and its work process of translating urban climatic information and analysis into planning recommendations.
Secondly, based on the UC-AnMap, the UC-ReMap is developed by refining the urban climatic class into urban climatic planning zones with relevant key planning recommendations from the urban climatic point of view. Some key parametric understanding of UC-AnMap for planning purposes – building volume, building heights, green areas, ground coverage, and air paths etc., on an area average basis, have been incorporated in the earlier part of the report for reference.
1.2 PURPOSE OF THE UC-REMAP
The UC-ReMap is an information platform and is planning oriented. With reference to the UC-AnMap, urban climatic planning zones can be formulated. For example, in Germany, different planning actions are recommended under various urban climatic planning zones of the UC-ReMap. The formulation of the UC-ReMap involves the collaboration between the planners and the urban climatologists with the UC-AnMap as their reference. The UC-
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ReMap provides the planners with general urban climatic information upon which strategic and district planning analysis, plan-making, and development control can make reference to.
1.3 STATE OF THE ART OF FORMULATING THE UC-REMAP
Germany is a leading country in conducting urban climatic mapping studies. Nowadays, the methodology of formulating UC-Map used in Europe, Asia and South America is mostly adopted from the German experience and followed the Association of German Engineers (VDI) Guidelines on Environmental Meteorology - Climatic and air pollution maps for cities and regions (VDI3787 Part 1). In Germany, based on the UC-AnMap and the UC-ReMap, planning advices are formulated by urban climatologists and planners with an aim to improving the urban climate of the city (e.g. mitigating urban thermal stress and improving thermal comfort). The main planning recommendations focus on reducing thermal load and improving dynamic potential through: . controlling building volumes and reducing coverage of ground surface; . preserving, maintaining and improving the existing urban ventilation paths and network of the city, charting new air paths if necessary; . Preserving, maintaining, improving and respecting the cool air production and drainage areas of the countryside and vegetated hillsides near urban areas; . Preserving, maintaining, improving and respecting the land-sea breezes; . Preserving, maintaining and improving urban greenery.
1.4 MODUS OPERANDI OF UC-REMAP FOR HONG KONG
The UC-ReMap provides an urban climatic based planning information platform at city and district scale of operation. When preparing the UC-ReMap for Hong Kong, due regard is paid to the existing planning framework of the area, the pre-defined OZP boundaries (Figure I-113) and broad groups of OZP areas with similar characteristics – bearing in mind that they may not always follow the urban climatic planning zones and urban climatic understandings.
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Figure I-113 A map of OZP coverage of in Hong Kong15 (as at 4.5.2012)
15 Refer to OZP index at www.ozp.tpb.gov.hk/ for details of the latest OZPs
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PART I(C)-2 DESKTOP STUDY FOR UC-REMAP
2.1 CASE STUDY – STUTTGART, GERMANY
2.1.1 Background and Context
Geography: Located in southern Germany; Total area is 207 km2 Urbanised area is 49% (102 km2) Forest area is 25%;
Population: Total population is 590, 000; Population density is 2,850 /km2
Topography: Lowest point is 207m above sea level; highest point is 549m above sea level
2.1.2 Planning Recommendation Maps
The planning recommendation map for Stuttgart contains an integrated assessment of the urban climatic analysis map and the related planning concerns. The map provides recommendations as to the sensitivity of different areas to changes or intensification in land
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The general planning advices of the UC-ReMap provide planners in Stuttgart with a generic and strategic basis upon which further detailed analysis/discussion can be carried out together with their in-house urban climatologists.
Figure I-114 Planning Recommendation Map for Stuttgart Stuttgart, Germany Planning Recommendation Map
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Table I-31 Planning Advices of Stuttgart Planning Recommendation Map
Open Spaces
Open areas with [HIGH urban climatic importance]: [Urban Climatically important open areas as they are directly related to the housing areas; high urban climatic sensitivity with respect to change of land use.
Open areas with [LESS urban climatic importance]: Little direct relationship to populated areas of activity; low urban climatic sensitivity with respect to change of land use.
Open areas with [LOW urban climatic importance]: No direct relationship to populated areas of activity; not urban climatically sensitive with respect to change of land use.
Built-up Areas
Built-up areas with small relevance to climate: No appreciable sensitivity in terms of climate/air pollution with respect to intensification of use and building agglomeration.
Built-up areas with some relevance to climate: Low sensitivity in terms of climate/air pollution with respect to intensification of use, e.g. consolidation, closure of gap sites etc. Built-up areas with a significant relevance to climate: Considerable sensitivity in terms of climate/air pollution with respect to intensification of use. Built-up areas with disadvantages in terms of climate/air pollution: Agglomerated settlement areas or buildings with a disturbing effect; In need of renewal from the point of view of urban climate. Streets with high emissions of pollutants and noise: Pollution forecasts are required, depending on the intended use, for planning of the area affected by the streets.
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2.2 CASE STUDY– TOKYO, JAPAN
2.2.1 Background and Context
Districts: As an administrative region of Japan, it consists of 23 central ―special wards‖ and many suburban cities.
Geography: Near the center of Japan, occupying 2,187 km2 in area.
Population: Total population is 13 million, which is about 10% of the total population of Japan; Population density is 5,796 / km2.
2.2.2 Investigation on the Environmental Impact of UHI by MoE (ヒートアイランド現象による環境影響に関する調査検討業務) Since 1998, the Ministry of the Environment (MoE) has begun to investigate the environmental impact of Urban Heat Island (UHI) and tried to find the possible measures for improving the thermal environment. Tokyo Metropolitan Area‘s 23 wards were chosen to be studied. UC-AnMap is one of their key efforts to analyse the urban thermal environment, through which a number of recommendations were made.
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2.2.3 Tokyo Thermal Environment Map
In April 2005, the Tokyo Metropolitan Government (TMG) produced a ―Tokyo Thermal Environment Map‖ (Figure I-115) (basically similar to an UC-AnMap although with a focus on thermal load). It presents the effects of thermal load and the condition of ground surface which contribute to the UHI phenomenon in Tokyo‘s 23 wards. Based on 17 regional factors contributing to the UHI effect, the areas of Tokyo have been grouped into five types based on their thermal environment characteristics and land use. The map has been plotted into raster with 500m x 500m grids and colour coded.
According to the urban climatic information and evaluation from the thermal environment map, the recommendations enable the TMG to identify four designated areas (Urban center district [Central Area], Shinjuku district, Osaki & Meguro Area and Area around Shinagawa Station) (東京都環境局都市地球環境部計画調整課, 2005) for further study and implementation of countermeasures against UHI for Tokyo‘s future urban renewal (Table I-32).
Figure I-115 Thermal Environment Map for Tokyo’s 23 wards and four designated areas (東京都環境局都市地球環境部計画調整課, 2005) Tokyo Metropolitan Area’s 23 Wards, Japan Thermal Environmental Map
Central Area
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Table I-32 Four Designated Areas
Name Area (ha) Characteristics Examples of Initiatives . Examine and The substantial heat load is implement ―wind or derived from artificially covered ventilation paths‖ to surfaces such as office building/ facilitate clear asphalt paving and excessive Central avenues for breezes 1,600 exhaust heat from buildings. Area to pass through the The temperature is high all day city; long. . Water retentive
paving
. Greening The substantial heat load is derived from artificially covered surfaces such as office . Water retentive Shinjuku 600 buildings, houses and asphalt paving Area paving. The temperature is high . Greening all day long.
Substantial heat load is derived from the ground surface, which . Water to be sprayed Osaki & makes it difficult for this dense using a road Meguro 1,100 residential zone to cool down at sprinkler Area night. (Area characterized by . Greening many tropical nights)
Extensive developments are . Examine and expected in the future and urban implement ―wind or Area development projects are to be ventilation paths‖ around carried out according to the plan 600 facilitating clear Shinagawa with preliminary consideration avenues for breezes Station given to heat island to pass through the countermeasures. city.
2.2.4 Guidelines for UHI Mitigation Measures
Consequently, with further detailed parametric studies based on the thermal map and the planning recommendations of the 4 identified key areas contained in Table I-32, in July 2005, the Tokyo Metropolitan Government further developed the ―Guidelines for UHI Mitigation Measures‖ (Table I-33) to encourage the central government and all parties concerned including private business to work together on improving the thermal environment for Tokyo.
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Table I-33 Menu of Heat Island Control Measures in the Problem Areas of Tokyo Menu of Heat Island Control Measures in the Problem Areas of Tokyo Area
Types Main areas Characteristics of each area Effective measures
Areas where thermal loads from the covering of the ground Around Kanda Station, surface are large day or night, and south of Ueno Station anthropogenic waste heat (sensible to around Okachimachi Main required heat) generated by buildings, etc. in Station, measures are to reduce the daytime is great. around Shinbashi the artificial covering . The percentage of the area of Station, around Ginza and anthropogenic the pavements in the road is the Station, around Tsukiji waste heat. highest at 55% and the percentage Station, around Mita Effective measures are of the area of the artificial covering Station, around to prevent heat from including buildings is also the Gotanda Station, being stored in highest at over 90%. around Shibuya buildings and the . In the daytime, approximately Station, Kabuki-cho, pavements and to Type 160 W/m2 of anthropogenic waste I-1 Shinjuku Ward, reduce waste heat from heat (sensible heat) is released and around Takadanobaba buildings, etc. this figure is the second largest Station, around among the areas in the type I. Ochanomizu Station . The percentage of the area of
the refractory walls is the highest. Menu of control measures* Greening Greening of Increased Water - Reductions in Rooftop of the building reflectance of retentive waste heat from greening premises** walls rooftops pavement buildings, etc. ○ ◎ ◎ ◎ ◎ ◎
Main areas Characteristics of each area Effective measures Higashi-Ueno, Taito Areas characterised by large Ward to Nishi-Asakusa, thermal loads from the covering of Ryogoku Station to the ground surface, day and night. around Oshiage Station, . The percentage of the area of around Iriya Station, buildings is high and the around Minowa Station, Main required
percentage of the area of the Type I (Crowded business area) Type(Crowded I
around Kitasenju measure is covering artificial covering is also as high Station, around installation and an as a little under 90%, which is the Kameido Station, effective measure is to second largest among the problem Okubo Station to install covering that areas in the type I. around will not store heat in . Among the areas in the type I, Type Shin-Okubo Station, buildings and the the average height of buildings is I-2 around Togoshi Station, pavements. the lowest and the width of around south of buildings is also the smallest, so Oimachi Station, that the shade is hard to appear on around Shimokitazawa the ground. Station, around
Sangenjaya Station Menu of control measures* ## Greening of Increased Water - Reductions in Greening of Rooftop building reflectance of retentive waste heat from the premises greening walls rooftops pavement buildings, etc. ◎ ◎ ○ ◎ v◎ △
Main areas Characteristics of each area Effective measures
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Type Area characterised by large I-3 anthropogenic waste heat (sensible heat) from buildings, etc. day and night. Around Roppongi Station, around Iidabashi Station, . The percentage of the area of around Hatchoubori buildings is small among areas in the Main required Station, around north of type I. measures are to reduce Shinjujuku-Gyoen-mae . In the daytime, approximately anthropogenic waste Station, around south of 280 W/m2 of anthropogenic waste heat, and an effective Omotesando Station, heat (sensible heat) is released and measure is to reduce around Takaido Station, approximately 160 W/m2 in the waste heat from Hachimanyama, Setagaya nighttime also, these figures are the buildings, etc. Ward, Yumenoshima, largest among the areas in the type I. Koto Ward, Keihinjima, Ota Ward
Menu of control measures* ## Greening of Increased Water - Reductions in Greening of Rooftop building reflectance of retentive waste heat from the premises greening walls rooftops pavement buildings, etc.
◎ ◎ ○ ◎ ○ ◎
Main areas Characteristics of each area Effective measures
Area characterised by large Around Nishi-Oi thermal loads from the covering of Station, around the ground surface in the daytime. Nakanobu Station,
around west of Nishi- Main required . The percentage of the area of Koyama Station, Nishi- measure is to reduce buildings is the highest among the Shinagawa, Shinagawa the covering and an areas in all types but the Ward, around south of effective measure is to percentage of the area of Asagaya Station, install the covering refractory rooftops is the smallest around south of Koiwa that do not store heat (the percentage of non-fireproof Type Station, around in buildings and the buildings is large). II-1 Machiya Station, ground surface. . The percentage of around north of Jujo anthropogenic waste heat releases Station, around Kasuya is small. Station . The average size of buildings is relatively small.
Type II (Crowded residential area) residential Type(Crowded II
Menu of control measures* ## Greening of Increased Water - Reductions in Greening of Rooftop building reflectance of retentive waste heat from the premises greening walls rooftops pavement buildings, etc. ◎ ○ △ ◎ ○ △
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Main areas Characteristics of each area Effective measures
Musashi-Koyama Area characterised by large Main required Station to around Fudo- thermal loads from the covering of measure is to reduce the Mae Station, around the ground surface, day and night covering and an effective Hatanodai Station, measure is to install the around west of Okubo . The percentage of the area covering that do not store Station, Tomihisa-cho, of buildings is high and the heat in buildings and the Shinjuku Ward to percentage of refractory ground surface. Ichigaya Daimachi, rooftops is the highest among Measures carried out in around south of Yutenji the areas in type II. fireproof buildings that Station, Shin-Nakano . The percentage of store heat till night are Station to around anthropogenic waste heat particularly effective. Type Nakano-Shinbashi (sensible heat) release is small. II-2 Station, around . The average size of Nishi-Sugamo Station, buildings is relatively small. around Mikawashima Station, around Keisei Hikifune Station, around Ojima Station Menu of control measures* ## Greening of Increased Water - Reductions in Greening of Rooftop building reflectance of retentive waste heat from the premises greening walls rooftops pavement buildings, etc.
◎ ◎ ○ ◎ ○ △
◎: Highly effective measures; ○: Effective measures; △ : Modestly effective measures
This menu of control measures is intended for types I and II with relatively heavy thermal loads. The guidelines spell out control measures also for types III to V. * This menu of control measures has been established based on the degree of the effectiveness of control measures which are weighed by the reductions in sensible heat that have been achieved by the control measures. The effectiveness of the control measures was estimated using the Urban Climate Simulation System (UCSS) developed by the Ashinaga Building Research Institute. ** At the time of reviewing this simulation, greenery by planting trees on the premises is assumed to be included in greening of the premises.
## Greening of the premises, rooftop greening, greening of building walls – increase trans-vaporation, enable better sensible heat conversion to latent heat, reduce artificial covering, provide shading to surfaces and reduce heat storage, and thus reduce the cooling loads of buildings.
Increase reflectance of rooftop – reduces heat absorption and thus reduce surface temperature and reduce the cooling loads of buildings.
Water retention pavement – increase sensible heat to latent heat conversion and reduces urban air temperature.
Reductions in waste heat from buildings – reduces sensible and latent heat release into the urban environment.
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2.3 LESSONS FROM CASE STUDIES
The Study has taken reference from the German Guideline VDI3787 Part1: Environmental meteorology-Climate and air pollution maps for cities and regions. Two case studies (the City of Stuttgart and the Metropolitan areas of Tokyo) have been conducted,which have revealed some key lessons for preparing Hong Kong‘s UC-ReMap.
. Urban climatic information and knowledge of the Thermal Load and Dynamic Potential characteristics of the UC-AnMap are the basis for formulating the recommended planning actions. The UC-ReMap provides a holistic platform of information for planning decision making and actions.
. The UC-ReMap provides an urban climatic based planning framework typically at the city and district scale of operation. Further studies at local planning scale are commonly needed for more detailed understanding and application.
. The UC-ReMap provides planning recommendations based on an evaluation of a number of planning parameters, including building volume, building heights, ground coverage of buildings, greenery coverage, air paths, and breezeways.
. The UC-ReMap presents a spatial evaluation of current urban climatic characteristics and identifies problem areas and climatically sensitive areas that are in need of strategic planning attention and improvement, for example:
a) According to the Tokyo Thermal Environment Map, the Tokyo Metropolitan Government has identified 4 designated areas where investigations have been done to identify appropriate improvement actions. b) In the City of Stuttgart, the ventilation corridors are highlighted as highly climatically sensitive areas in urban development, which should be respected and preserved with low roughness (i.e. the area should be open or only covered by low-rise buildings) for transfer of the fresh cool air to central urban area for mitigating the UHI effect.
. The UC-ReMap focuses on improving or preserving the existing greenery and open space, creating or protecting the ventilation path/corridor, and reducing the thermal load in built-up areas. They aim to mitigate the UHI effect and to improve outdoor thermal comfort and thus living quality, for example:
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a) For the City of Stuttgart, based on the UC-ReMap, the local government can conduct focused studies in order to update the Master Plan of Greenery. The focused studies have identified zones that prohibit tall buildings and/ or intensification of use, as well as for defining air paths. b) For the 4 designated areas identified in the Metropolitan Area of Tokyo, the urban climatic planning recommendations focus on improving building materials, ground surface cover, greening and reducing anthropogenic heat release. In the subsequent study of Kaze-no-michi (Ventilation Path) for one of the identified areas, the recommendations focus on encouraging sea breeze penetration into the inner urban areas, and enhancing greenery.
. The UC-ReMap itself is not a regulatory instrument (it is only an information platform). It however facilitates a participatory planning process by providing urban climatic information useful for the planning process.
PART I(C)-3 METHODOLOGY OF THE UC-REMAP FOR HONG KONG
3.1 PROCESS AND A PARAMETRIC UNDERSTANDING
The evaluation on thermal comfort and relevant climatic understanding from the UC-AnMap are translated and developed into the UC-ReMap. Five Urban Climatic Planning Zones and relevant general urban climatic planning recommendations are formulated and explained.
The following work procedure (Table I-34) is adopted to develop the UC-ReMap and Climatic Planning Advices for Hong Kong:
Table I-34 Work Process of the Hong Kong UC-Re-Map Overall Approach: Translate the urban climatic information and understanding from the UC-AnMap to UC-ReMap
A Based on the UC-AnMap, the 8 urban climatic analysis classes are consolidated into 5 Urban Climatic Planning Zones (UCPZ) according to urban climatic characteristics and planning implications. ↓ Based on A, key planning recommendations of the 5 UCPZs of the UC-ReMap B are formulated and elaborated. In preparation of the UC-ReMap, references have also been made to the discussion in the Technical Experts Engagement Workshop conducted in February 2009.
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3.1.1 Input Information for UC-ReMAP – the UC-AnMap for Hong Kong
The UC-AnMap with an appreciation of the OZP boundaries of Hong Kong is the key input information for generating the UC-ReMap. The UC-AnMap is reported at 100m x 100m grid. With this resolution, climatopes patterns based on Thermal Load and Dynamic Potential of the urban morphology at a scale necessary for planning could be derived. The spatial distribution of wind information has also been included in the UC-AnMap.
3.1.2 Key generic interpretation of the urban climatic parameters for planning recommendations The UC-AnMap takes into account various urban climatic related planning parameters as GIS input layers. They are then synthesised based on the parameters‘ respective thermal load and dynamic potential impacts. Physiological Equivalent Temperature (PET) is used as the consolidating indicator to measure the various parameters‘ positive and negative effect on urban climate (Table I-36).
Table I-36 Parameters and layers of UC-AnMap Physical PET Effect Scientific Basis Input layers Criterion Categories Layer 1 0 to 5 Negative Building bulk Building Volume Map Thermal Altitude and Layer 2 -3 to 0 Load Elevation Topographical Height Map Positive Layer 3 -1 to 0 Bioclimatic effects Green Space Map Layer 4 -2 to 0 Negative Urban permeability Ground Coverage Map 0 to 1 Dynamic Bioclimatic effects Layer 5 Potential - Cold air movement Natural Landscape Map Positive Air mass exchange Layer 6 -2 to 0 and Neighbourhood Proximity to Openness effects Map MM5 Simulation and Layer 7 - Wind - HKO field Prevailing Wind Directions Information measurements (Summer)
Layer 2 (topographical height) and Layer 5 (natural landscape) are largely ―given‖ and basically fixed. Layer 1 (building volume), Layer 3 (green space), Layer 4 (ground coverage) and Layer 6 (proximity to openness) are considered to be useful parameters in formulating appropriate planning controls and actions to address problem areas (Table I-37).
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Table I-37 UC-AnMap layers and planning parameters
Building Higher building volume leads Building volume, building density, floor Volume to higher PET area ratio and plot ratio Green Space Higher green space leads to Greenery and tree planting, city parks lower PET Ground Higher ground coverage leads Non building areas, building set back, open Coverage to higher PET spaces, building site coverage Proximity to Proximity to openness leads Waterfront, hillside, large open spaces and Openness to lower PET parks
3.1.2.1 Building Volume The planning parameter of Building Volume has an implication on Thermal Load. The quantitative effect of Building Volume on PET values has been studied. The investigation has selected 17 urban areas (Figure I-116) with mostly Class 4 and 5 UCPZs [site no. 1 to 17 in Table I-38], and 2 urban areas with mostly Class 3 and 4 UCPZs [site no. 18 to 19 in Table I-38] from the UC-AnMap. The building site area ratios (BSAR), i.e. the ratio of building site area to the total site area, of the test areas are calculated. The BSAR16 is typically found to be in the order of 50% in less dense areas like Fanling and Tai Po and at 60 to 70% in denser areas of Hong Kong (Figure I-117 and Table I-38).
16 For example, for a BSAR of 60%, 40% of the area will be open area. If 50% of the building site is not built upon (i.e. site coverage of 50%), another 30% (i.e. 60% x 50%) of the area will be open as well. The total open area will be 40% + 30%, i.e. 70%, and the ground coverage will only be 30%
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for comparsion purpose
Figure I-116 The selected dense urban areas of Hong Kong
Building Site Area Ratio 80% (BSAR) 70%
60%
50%
40%
30%
20%
10%
0%
Site 0 Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9 Site
Site 11 Site 12 Site 13 Site 14 Site 15 Site 16 Site 17 Site 18 Site 19 Site Site 10 Site Figure I-117 Building Site Area Ratio of the selected dense urban areas of Hong Kong
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Table I-38 The selected dense urban areas [designated and focused] for the calculation of TBV, BV on BSA, BVD, GC, SGC, BSAR and FAR Site No. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Test area (S) (km2) 0.12 0.74 0.32 0.63 0.68 0.39 0.43 0.64 0.61 0.5 0.49 0.47 0.42 0.48 0.56 0.91 0.83 0.82 0.57 0.51 Central, Causeway Quarry Hung Sheung Tsim Yau Cheung Lai San Central Bay & Kwun Tsuen Wan North Bay & Mong Sham Hom & Tuen Yuen Tai Fan- Wan & Sha Ma Sha Chi Po Location # East Wan Tong Wan Chai Point Shau Kei Kok Shui Po To Kwa Mun Long Po ling Sai Ying Tsui Tei Wan Kok Kong Chai Wan Wan Pun Building Site Area 0.57 0.65 0.59 0.72 0.61 0.57 0.65 0.71 0.66 0.58 0.6 0.61 0.63 0.65 0.6 0.71 0.72 0.54 0.51 0.49 BSA (km2) Total Building Volume TBV 46 19 24 20 22 21 21 21 17 12 17 11 11 19 14 12 16 8 7 5 [(„000,000) / km²] (m3) BV on BSA 45 17 23 20 21 20 21 20 17 11 16 11 11 18 13 12 15 7 6 5 [( „000,000) / km²] Building Volume 38% 15% 20% 17% 18% 17% 18% 17% 14% 10% 14% 9% 9% 16% 12% 10% 13% 6% 5% 4% Density BVD (%) Ground Coverage 49% 42% 41% 49% 44% 40% 44% 43% 44% 36% 42% 40% 35% 48% 44% 31% 34% 28% 25% 26% GC (%) Site Ground 86% 64% 69% 68% 72% 70% 68% 60% 66% 63% 70% 65% 56% 74% 72% 43% 47% 52% 49% 53% Coverage SGC (%) Building Site Area 57% 65% 59% 72% 61% 57% 65% 71% 66% 58% 60% 61% 63% 65% 60% 71% 72% 54% 51% 49% Ratio BSAR (%) Floor Area Ratio FAR ~20 7-9 10-13 7-9 9-11 9-12 8-11 7-9 6-8 5-6 7-9 4-6 4-6 7-10 6-7 4-6 5-7 3-4 3-4 2-3 (fl.ht. 4.0 to 3.0 m)
S = Size in km² of test areas of the various locations; Building Site Area (BSA) includes all land use zones that can be built on within S ##, normalised to 1 km²;
Total Building Volume (TBV) = total above ground building volume in S, normalised to 1 km² for cross comparative purpose among various locations; (BV on BSA) = above ground building volume on BSA in S, normalized to 1 km² for cross comparative purpose among various locations; Building Volume Density (BVD) [For the definition of BVD, please refer to Part I],17 in this case, the understanding is area averaged for S; Ground Coverage (GC) = total built over area in S / S, in this case, the understanding is area averaged for S; Site Ground Coverage (SGC) = GC / BSAR, in this case, the understanding is area averaged for S; Building Site Area Ratio (BSAR) = BSA / S, the understanding is area averaged for S; Floor Area Ratio (FAR) = [(BV on BSA) / floor height] / BSA, and the floor to floor heights (fl.ht.) are taken to be 4.0 to 3.0 (m), the understanding is area averaged for S; # For comparison purpose, an area of 300x400 m in Central (Site No. 0) with very high BVD is included as an illustration only ## Building Site Area includes Residential, Commercial, Industrial, Government, Institution & Community Facilities, and Other Urban or Built-up Land
17 Building Volume Density in % (BVD) is the above ground building volume in m3 of a 100m x 100m grid of land divided by a datum value of 1,217,000 m3
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By assuming typical building floor heights to be 3 to 4m, the 3-dimensional building volume understanding can be translated to the 2-dimensional floor area understanding. Since the UC- AnMap only considers above ground building volume, only above ground floor areas are accounted for. With the assumed building height and calculated BSAR, the threshold area average Floor Area Ratio (FAR) can be estimated. In contrast to Plot Ratio (PR) 18, FAR accounts for all above-ground floor areas including concessionary GFA, and is practically and realistically more directly related to building volume, and hence the thermal load understanding of the UC-AnMap. There is, however, no fixed and direct conversion between FAR and PR. In order to estimate the PR equivalent of FAR, a range of FAR to PR ratios of 1.2 to 1.5 have been used in column 5 of Table I-39, based on a recent study by the Development Bureau, HKSAR Government.
In the urban context of Hong Kong, given its high PR, high FAR and tall building heights, the focus is mostly in PET categories 3 or 4 of the building volume layer of the UC-AnMap. For planning purpose, on an area average basis, it is useful to note the threshold values of about “3”, “7” and “10” FAR being the upper limit of UC-AnMap PET categories 2, 3 and 4 respectively in the dense urban areas. It may be useful to make reference to these values when working out the allowable PR of various sites when taking into account concessionary GFA (Column 5 of Table I-39). When determining the threshold of 3, 7 and 10 in reading Table I-39, the principle of ―leniency‖ for the less critical low density conditions and the principle of ―prudence‖ for the more critical high density conditions have been used.
In areas having wider streets and more open spaces, on an area average basis, BSAR will be slightly lower (around 50 to 60%). It is therefore possible, if needed, to adopt a slightly higher FAR for such areas than areas having narrow streets and few or no open spaces (i.e. BSAR of 60 to 70%). In such areas, a threshold of FAR=8 may be used for UC-AnMap PET categories 3 and 4. However, it may be better, urban climatically speaking, to preserve/maintain these areas without bringing their densities up to the threshold.
18 Refer to the table in the Legislative Council Panel on Development (19 Dec 2008) paper titled ―Ranges of GFA Concessions Granted as a Percentage over Actual GFA of Sample Buildings‖. (http://www.susdev.org.hk/download/GFA_Concessions_Study_eng.pdf) Since 1 April 2011, the PNAP APP-151 takes effect and imposes a cap of 10% on GFA concessions for non-mandatory/non-essential plant rooms and services and specified green/amenity features, whilst the provision of facilities or features eligible for GFA concessions (e.g. mandatory features or essential plant rooms) are still subject to technical criteria laid down in relevant regulations under the Building Ordinance and/or design guidelines promulgated by the Building Department.
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Table I-39 The relationship between Building Volume Density (%) and Floor Area Ratio (1) (2) (3) (4) (5)
UC- Building =[(2) x 1.217 Floor Area Ratio (FAR) Plot Ratio AnMap volume density million m3 / = [(3) x Approximate Floor =(4) / (FAR/PR) Building (BVD) % fl.ht.(m)]/Appr Area (m2)]/ [grid (m2) x BSAR] Volume oximate Floor 2 Layer Area (m ) - PET categories
In UC-AnMap, Assume Assume average building site area BSAR=60% BVD= 100%, Its approximate (Building Site Area) to 100x100 value =1.217 floor area = 2 Assume FAR/PR of 2 grid ratio of … in an 1 km urban million m3 1000 m area BSAR (%) Assume fl.ht. =3 to 4m BSAR BSAR BSAR 1.2 1.5 50% 60% 70% 0 0 0 0 0 0 0 0 1 0 and paved 0 0 0 0 0 0 ~to ~ to ~ to ~ to ~ to 2 0 to 4% ~ to 12-16 2.4-3.2 2.0-2.7 1.7-2.3 1.7-2.3 1.3-1.8 ~to ~ to ~ to ~ to ~ to 3 4 to 10% ~ to 30-40 6.1-8.1 5.1-6.8 4.3-5.7 4.3-5.7 3.4-4.5 ~to ~ to ~ to ~ to ~ to 4 10 to 25% ~ to 75-100 15.2-20.3 12.7-16.9 10.9-14.3 10.6-14.1 8.5-11.3 > > > > > 5 25 to 100% > 75-100 15.2-20.3 12.7-16.9 10.9-14.3 10.6-14.1 8.5-11.3
In medium/high density areas, on an area average basis, a FAR in the range of 6 to 7 can be suggested as being ―reasonably optimal‖. To limit the increase in thermal load due to building volume, from a planning point of view, on an area average basis, it is recommended that FAR of 7 19 be adopted as the threshold from the outset, subject to consideration of other relevant factors. FAR of 8 to 9 is occasionally possible subject to provision of effective mitigation measures. In any case, FAR of more than 7 would demand careful design. Based on the Hong Kong UC-AnMap thermal comfort formulation, ―Hot - Strong‖ heat stress can be experienced under category 4 (4 ○C) of PET increase; this should be avoided. Higher FAR, if needed, is possible subject to mitigation measures like greening and reducing ground coverage. As shown in Table I-38, on an area average basis, most of the concerned areas in Hong Kong [e.g. areas in Central/ Sheung Wan, Causeway Bay, Kwun Tong, and Tusen Wan etc.] has FAR of 8 or above. Building Volume with FAR higher than 8 in high density areas (see Table I-39) may increase the thermal load significantly; as such, careful scrutiny of building volume is essential, and mitigation measures must be implemented.
It is important to bear in mind that the correlation between building volume and thermal load follows a logarithmic relationship, as evident in column 2 of Table I-39. This means that
19 Based on Table I-39, FAR of 7 for areas with BSAR 50%, +3 degrees in PET; for areas with BSAR 60%, +4 degrees (marginally); and for areas with BSAR 70%, +4 degrees.
School of Architecture, CUHK Page 199 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT whilst it is very effective to control building volume alone, and thus the urban thermal load in the range of FAR of 1 to 5, it is less effective when FAR is 6 or above. Other mitigation measures are also necessary and can be more effective in these high density areas. In the dense urban areas of Hong Kong, unless FAR can be dramatically reduced, given the already high FAR commonly practised, building volume control [and thus building height 20 21 and plot ratio control] must be complemented with other mitigation measures such as improving air paths, reducing ground coverage and increasing green spaces.
Overall, on an area average basis in planning terms, reducing/maintaining Building Volume in low/medium density areas with FAR of 1 to 5 is very effective and beneficial to lowering urban thermal load. In medium/ high density areas, FAR in the range of 6 to 7 can be suggested as ―reasonably optimal‖ when buildings are carefully designed. FAR of 8 to 9 is occasionally permissible but would require mitigation measures. In very high density areas, a FAR above 10 will increase the thermal load significantly, therefore careful scrutiny of building volume is essential and mitigation measures are required. To limit the building volume contribution to thermal load, it is recommended that FAR of 7 be adopted as a working threshold from the outset.
With regard to building height, based on the buildings‘ aerodynamic understanding of various flow regimes – isolated roughness flow, wake interference flow and skimming flow - it is effective to enhance air ventilation by controlling building heights in low/medium density areas with building height/street width ratio (H/W) of 2 and below. In general, varying building heights is useful to enhance turbulent mixing and improve dynamic potential. For urban areas with H/W of 2 or above, non-uniform building height bands of sufficient height contrast would be more effective to enhance air ventilation. Other parallel measures such as providing air paths or breezeways should be considered as well to enhance their effectiveness.
20 An urban area of varying building heights is typically better than one with uniform and monotonous heights. This is because of the higher turbulence and greater sky view factor (SVF) differentials that different heights of buildings of an urban area can create; this encourages mixing and is beneficial to pedestrian level urban ventilation; and this also results in higher overall SVF and hence assists urban heat dissipation. Variations of building heights do not mean a difference of a few, 10 or 20 meters. It means building height contrast of 0, 0.25, 0.5, 0.75H, H being the tallest building, randomly distributed and arranged in the area. This guiding principle should be applied with care and the building height controls/relaxations resulted should be justifiable taking into account other planning considerations.
21 Khan I M et al (2004) Effect of local and upstream geometry on flow dynamics in urban environment, in Proceedings of the International Conference on Urban Wind Engineering and Building Aerodynamics – Cost Action C14, Impact of Wind and Storm on City Life and Built Environment, edited by J P A J van Beeck, von Karman Institute for Fluid Dynamics, May 2004. [ISBN 2-930389-11-7] quoted as follows: ―Uniformity in height of buildings along parallel streets in an urban environment promotes shear at roof- level, thereby trapping fluid … within the canyon. … On the other hand, non-uniformity in building height and the presence of substantial upstream buildings promotes turbulence which helps in ventilation of street canyons. … the objective should be to reduce shear at roof-level and promote turbulence.‖
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Given the same FAR / PR, increase in floor-to-floor height will increase the building volume and thus the thermal load. Therefore, unreasonably high floor-to-floor height is not encouraged.
3.1.2.2 Greenery
Figure I-118 Greening, especially tree planting, is encouraged at ground or podium level for better cooling of the urban environment at the pedestrian level
Greening is beneficial to the amenity of the urban environment and also urban climate (Figure I-118). A survey study in Hong Kong (Lo et. al., 2003) shows that microclimate is the most important criterion for urban open space users in Hong Kong, followed by the lesser criteria of soft landscape, seating and hard landscapes. Among the sub-criteria, planting far outweighs the importance of the other criteria. This in turn reinforces the importance of microclimate as planting performs most of the functions in regulating microclimate of urban open spaces (Figure I-119).
Figure I-119 Global weightings for sub-design criteria
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In general, based on the CUHK‘s study of effect of the planning parameter of Green Space on Thermal Load using Envi-Met model simulation22, an area average of 30% of greenery coverage, with a mixture of tree planting (50%) and grass coverage (50%) in a 100mx100m grid, would lead to a reduction in one PET (Wang & Ng, 2010). Tree planting is far more effective than grass covering, as their canopy not only cools the air space at the pedestrian level, but also provide shading and thus lower direct radiation from the sun. Similarly, intensive tree planting with trees of high leaf area index 23 (>4 to 6, i.e. dense leaf canopy (Bréda, 2003)) is found to contribute to a reduction in 2 PET. On the other hand, grass mainly reduces the surface temperature and thus only lowers mainly the Tmrt [Mean Radiant Temperature] of the environment.
Pockets of green oasis, that is to say, large area (~ 70m x 70m) of tree planting, in urban areas are useful in providing localised thermal reliefs to the urban environment (lower PET by 1 to 2 classes for the immediate vicinity). Taking into account human thermal adaptation, in high density areas, they are extremely useful in providing thermal diversity to the built environment, such that people can choose and experience a cooler locality in the midst of high-rise developments. The effectiveness of these oases can be increased if air path connectivity, as explained later, can also be implemented.
For the purpose of counting the crown area of trees, a study by Professor CY Jim has indicated that the majority of trees in urban Hong Kong has crown diameter of less than 5m, with the mean being around 2-3m (Jim, 1998).
3.1.2.3 Ground Coverage
In Hong Kong, given the already high building density and building volume, reducing ground coverage is a useful strategy to encourage air ventilation and therefore lowering the PET (Table I-40). For planning purpose, in high density areas, it is useful to note the ground coverage threshold values of around ―30%‖ and ―50%‖ being the upper limit of UC-AnMap Ground Coverage Layer PET category -2 and -1 respectively (Table I-40). For example, in
22 The CUHK study finding(Wang & Ng, 2010) is in line with the Sustainable Development Unit‘s recent engagement exercise titled Building Design to Foster Quality and Sustainable Built Environment that recommended site greening of 20 to 25%; this is equivalent to 33 to 37% when it is normalised to the ―city area average understanding‖ of the UCMap. Japanese researcher Masakazu Moriyama has also recently obtained similar findings with his research in greening based in Osaka.
23 Leaf Area Index (LAI) is the ratio of total upper leaf surface of vegetation divided by the surface area of the land on which the vegetation grows. LAI is a dimensionless value, typically ranging from 0 for bare ground to 6 for a dense forest(Bréda, 2003). http://www.uni-giessen.de/~gh1461/plapada/lai/lai.html
School of Architecture, CUHK Page 202 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT urban areas where streets are narrow (e.g. in Sheung Wan and Kwun Tong), and Building Site Area Ratio (BSAR) is high i.e. 70%, it is important to consider measures such as providing non-building areas, building set back, as well as creating more open spaces so that the grid average ground coverage can be lowered to below 50%, with the grid average site ground coverage below 65%. Greening should be considered for the resultant non-building area [see the section on green space above for further information] (Figure I-120).
Figure I-120 Non-building areas (building set back) to reduce ground coverage is recommended. Greening is encouraged
Table I-40 The relationship between the planning parameter of Ground Coverage (%) and Site Gound Coverage (%) UC-AnMap Approximate Site Ground Coverage (SGC) (%) Ground Grid Ground ground area Assume building site area ratio (BSAR) in a Cover coverage covered (m²) in 100mx100m grid as follows: Layer PET- (GGC) a 100m x 100m BSAR 60 % BSAR 65 % BSAR 70 % categories grid -2 0 to 30 % 0 to 3,000 0 to 50 % 0 to 46 % 0 to 43 % -1 30 to 50 % 3,000 to 5,000 50 to 83 % 46 to 76 % 42 to 70 % 0 Over 50 % Over 5,000 > 82 % > 75 % > 70 % GGC = built over area / grid area of the UC-Map 100m x 100m grid. SGC = built over area / buildable land use zones within the grid area of UC-Map 100m x 100m grid.
3.1.2.4 Proximity to Openness and Connectivity The extensive coastline of Hong Kong is beneficial in allowing sea breezes into the urban area. From a strategic planning perspective, it is important to utilise this air movement by reducing ground coverage of developments near the waterfront, and create breezeways/air paths perpendicular to the waterfront to direct sea breezes inland (Figure I-121). Major breezeways can be around 100m in width or greater and should have very low ground roughness. Both landscaped and water channel breezeways are considered to be very effective in bringing cooler and cleaner air into the urban areas.
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With reference to BD‘s study24, for an urban area to benefit from its proximity to openness, a site permeability of 25 to 35% is suggested. Together with an aggregate of roads leading from the waterfront, open spaces, non-building areas, and gaps between buildings etc., this may result in an area average ground coverage equivalent to 50%; thus improving dynamic potential and lowering the UC-AnMap class.
Urban areas can also benefit from downhill air movement from vegetated hillsides. This katabatic air movement is basically gravity flow that can easily be stopped or interrupted by buildings and paved areas. It is therefore very important not to disturb the vegetation on these slopes. It is also useful to intensify them with further tree planting. To bring the katabatic air movement further into the urban area, it is useful to create ‗green fingers‘ to facilitate the flow. The key for urban permeability is to relate it with air ventilation connectivity; that is to say, the open spaces and air paths must be well connected.
Water – sea breezes
Reduced “thickness” “Thick” urban increases urban structure reduces permeability urban permeability
Vegetated hill slopes
Figure I-121 Ways of creating breezeways and air paths in the urban fabric
The free flow of air ventilation through the urban fabric (for example on the northern shore of the Hong Kong) can be greatly assisted by connecting the waterfront with the vegetated hill slopes through a ―connection‖ of breezeways, air paths, open spaces, greeneries, green oasis and ‗green fingers‘. Various connection strategies can be considered (Figure I-122).
24 BD‘s consultancy study on Building Design that Supports Sustainable Urban Living Space in HK [Buildings Department The Government of the Hong Kong Special Administrative Region (2009), Consultancy Study on Building Design that Supports Sustainable Urban Living Space in HK.]
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Figure I-122 Ways of creating breezeways and air paths in the urban fabric
Open spaces in the urban area allow the above roof-top wind to flow into them and benefit pedestrian air ventilation. In general, the dimensions of the open space should be no less than twice the average height of the surrounding buildings. This would create a height to width ratio of below 0.5.
3.1.2.5 A comparison of suggestions The Council for Sustainable Development‘s (SDC) public engagement exercise titled ―Building Design to Foster a Quality and Sustainable Built Environment‖ contains a number of suggestions, which are compared with the findings of this study (Table I-41). While the policy options set out by the SDC in its ―Invitation for Response‖ document are more related to individual building sites, recommendations in this UC-Map Study are district-based and derived from a strategic and comprehensive analysis of the urban climatic conditions of Hong Kong as a whole. However, they essentially complement one another.
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Table I-41 Suggestions of UC-Map vs. SDC’s exercise Site based measures General Planning Guidelines suggested in SDC’s IR Recommended under the UCM Document Study25 ● building separation requirement for Building Separation/ the middle and high assessment 20% to 33.3% building Building Setback/ zones as per PNAP APP-152 separation & set back at street ● building setback; Ground (Site) level in narrow streets. Coverage ●Ground coverage of not more than 65%. ● Greenery (preferably tree planting) of no less than 30% for sites larger Greenery than 1 ha, and 20% for sites below 1 20% to 30% of the site areas. ha at lower levels, preferably at grade. Sites smaller than 1,000m² are exempted. ● City area average threshold FAR Reviewing prevailing policies values of 3 to 7 are suggested; Building for granting GFA concessions, ● FAR > 7 would require some Volume/Capping GFA Concession including introduction of mitigation measures; overall / individual caps ● FAR > 10 to be very carefully scrutinised and mitigated. Building Permeability (at all Proximity to levels of the building) ●Air paths and „green fingers‟ Openness and Connectivity equivalent to 20% to 33.3% of ●Air path connectivitiy. total frontal area in large sites. ● Vary building heights; Building Heights Nil ● Excessive floor to floor height is not encouraged.
3.2 KEY ISSUES AND ANALYSIS
In line with international practice for UC-ReMap studies, especially the experience of German and Japanese researchers, the urban climatic analytical information are evaluated and interpreted into urban climatic planning zones (UCPZ) with planning recommendations devised.
25 The General planning guidelines recommended under the UCM Study are derived based on the urban climatic considerations at strategic/district levels. Since they are developed using the area average 100m ×100m grid understanding of the UC-Map and assuming urban homogeneity, they are intended to be district-based measures and not supposed to explain the micro scale details. The numbers suggested must not be directly adopted for site-based works. In determining appropriate development parameters for individual sites, apart from these general planning guidelines, reference should also be made to all strategic and district planning frameworks as well as individual site circumstances.
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According to the UC-AnMap information and its likely positive and negative impacts on human urban thermal comfort, for ease of definable planning actions, it was deemed reasonable to consolidate the 8 urban climatic (UC) classes of the UC-AnMap into 5 UCPZs of the UC-ReMap (Figure I-123 & Table I-42) in accordance with their urban climatic characteristics and planning implications.
UC Classes 1 and 2 covering urban climatically valuable areas with positive urban climatic impact should basiscally be preserved, and are therefore grouped into one UCPZ. Since the Study‘s thermal comfort survey had concluded that UC Classes 3 and 4 have ―neutral‖ and ―slight‖ thermal comfort impact, they can reasonably be grouped into one UCPZ. UC Class 5 indicates ―moderate‖ thermal comfort impact and will form a separate UCPZ. UC Classes 6 and 7 indicate ―moderately strong‖ to ―strong‖ thermal comfort impact and will be combined as one UCPZ. Finally, due to the severity of UC Class 8 (―with very strong‖ thermal comfort impact), it is considered to form a UCPZ of its own.
Figure I-123 The formulation of UCPZs for the UC-ReMap (Graphics used are indicative)
Table I-42 The 5 UCPZs of the UC-ReMap Impact on Thermal Urban Climatic Planning Strategic Planning No Urban Climatic Class Comfort Zone action 1 Moderate negative Thermal Load ●● and Good Dynamic Potential Moderate cooling Preservation 2 Some negative Thermal Load and ● Urban climatically valuable Good Dynamic Potential Slight cooling area
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3 Low Thermal Load and Good - Dynamic Potential Neutral Maintenance 4 Some Thermal Load and Some ● Neutral urban climatically sensitive area Dynamic Potential Slight warming ●● Some mitigation Moderate Thermal Load and Some 5 Dynamic Potential Moderate Moderate urban climatically actions encouraged warming sensitive area where possible ●●● Moderately High Thermal Load and 6 Low Dynamic Potential Moderately strong Mitigation actions warming High urban climatically recommended and ●●●● sensitive area necessary 7 High Thermal Load and Low Dynamic Potential Strong warming
●●●●● Mitigation actions Very High Thermal Load and Low recommended and 8 Dynamic Potential Very strong Very highly urban warming climatically sensitive area essential ● cooling thermal impact ● warming thermal impact
3.3 UC-REMAP – STRATEGIC AND DISTRICT PLANNING RECOMMENDATIONS
The 5 Urban Climatic Planning Zones (UCPZ) are as follow: . UCPZ1: Preservation . UCPZ2: Maintenance . UCPZ3: Some mitigation actions encouraged where possible . UCPZ4: Mitigation actions recommended and necessary . UCPZ5: Mitigation actions recommended and essential
The valuable urban climatic characteristics of UCPZ 1, which are cooler areas on higher ground and with better wind, should generally be preserved. Opportunities for mitigation within UCPZs 3, 4 and 5, which are subject to high thermal load and low dynamic potential, should be maximised. Hong Kong‘s long-term development needs may be accommodated in UCPZ 2 subject to prudent planning and design measures so as to maintain the existing urban climatic characteristics.
The 5 UCPZs are depicted in the UC-ReMap of Hong Kong (Figure I-124). Key planning recommendations at a district planning level are formulated based on the analysis and evaluation of the effects of the following planning parameters on thermal load or dynamic potential (see Table I-43): . Breezeway and air paths
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. Building volume . Ground coverage . Greenery . Natural areas and Cool air production / drainage areas . Open spaces
Their understanding is based on the various layers and urban climatic parameters as analysed in the UC-AnMap. In short, the following planning parameters can be controlled to help create a better urban climate:
Thermal Load understanding . Layer 1 Building volume density . Layer 3 Greenery
Dynamic Potential understanding . Layer 4 Ground coverage . Layer 6 Breezeway and air paths Natural areas, Cool air production / drainage areas Open spaces and proximity to waterfront
It is useful for the key planning recommendations of the UCPZs to be read in conjunction with the Wind Information Layer, which is also incorporated into the UC-ReMap. For example, when air path is referred to in a specific planning recommendation, this can be read with the prevailing wind direction of a particular ―wind region‖ and an understanding of minor modifications of the topography as indicated with the key wind arrows, to help determine initially, the direction of the desirable air path. Further detailed studies can then be based on this initial understanding.
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The Urban Climatic Planning Recommendation Map of Hong Kong 100m x 100m resolution, raster based
Figure I-124 The UC-ReMap, 100m×100m raster based, with wind information - prevailing wind directions (summer)
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Table I-43 General Recommendations for the 5 UCPZs Urban Climatic Strategic Key Planning Recommendations Planning Zone Planning action
1 Preserve the urban climatic conditions 2 Natural areas at higher altitude and with fewer obstructions to wind act as sources of cool air production and drainage areas, which are beneficial to other areas (e.g. vegetated hill slopes adjacent to urban areas) and should therefore be preserved. Sealing (covering of ground surface) or development should be discouraged. 1. 3 In view of its urban climatic value, there is a Urban Preservation general presumption against major climatically development in this zone. valuable area 4 Small-scale and essential developments may be allowed in areas other than in natural areas identified in 2 above subject to: (a) careful planning and design of these developments to minimise any disruption to the existing urban climatic characteristics; (b) maximising greenery and open areas; and (c) minimising sealing.
1 Maintain the urban climatic conditions 2 These zones are currently urban climatically ―neutral‖ in terms of urban thermal comfort. They are mostly urban fringe or rural lowland. It is important to maintain their climatic characteristics. 3 General urban climatic characteristics such as lower building volume, open spaces and greenery should be maintained as far as 2. possible.
Neutral urban Maintenance climatically 4 New low-density individual developments sensitive area could be allowed subject to: (a) a low building volume and a satisfactory disposition of buildings to align with the prevailing wind directions and preserve existing air paths; (b) a low ground coverage in order not to impede air flow; and (c) maximisation of greenery within development sites. 5 New comprehensive development is possible subject to thorough urban climatic
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consideration. Prudent planning and building design is necessary to avoid degrading the urban climatic condition. Breezeways and air paths must be carefully designed. Street grids and building disposition must respect prevailing wind directions. High building volume and ground coverage should be discouraged.
1 Some mitigation actions encouraged where possible 2 These zones are currently subject to urban climatically ―moderate‖ impact in terms of thermal comfort. They are mostly in the urban fringe or less dense development areas. 3 Additional development is permissible subject Some to : 3. mitigation (a) urban climatic evaluation in terms of Moderate urban building volume and green coverage; actions (b) dispositioning of new buildings in line climatically encouraged sensitive area with the prevailing wind directions, to where possible preserve/enhance existing air paths; (c) reduction of ground coverage in order not to impede air movement; and (d) maximisation of greening, particularly tree planting within development sites and adjoining streets. 4 Greening should be promoted in open areas as far as practicable.
1 Mitigation actions recommended and necessary 2 These zones are already densely built up. Thermal Load is high and dynamic potential is low. Some strong impact on thermal comfort is expected. 3 Air paths/breezeways, and low-rise, low- 4. Mitigation actions density ‗Government, Institution or High urban Community‘ (GIC) sites should be preserved climatically recommended as far as possible. sensitive area and necessary 4 Greenery, particularly tree planting on streets and open aress, should be increased. 5 Additional development should not be allowed unless with appropriate mitigation measures, including: (a) reducing ground coverage to balance against any increase in building volume; (b) respecting existing air paths and
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introducing new ones, if feasible; (c) positioning buildings to align with the prevailing wind directions; and (d) maximising greening within development sites.
1 Mitigation actions recommended and essential 2 These zones are already very densely built-up. Thermal Load is very high and dynamic potential is low. Very strong impact on thermal comfort is expected. Frequent occurrence of thermal stress is anticipated. 3 Intensification of GIC sites which serve as a relief to the existing condition should be avoided. Additional and intensified greening within the GIC sites is essential. 4 Additional greenery and tree planting on open areas and streets in this zone is essential and 5. Mitigation recommended. Intensified greening in ―Open Space‖ zones is strongly recommended. Very highly actions urban 5 The existing urban environment should be recommended improved by: climatically and essential sensitive area (a) identifying, respecting, widening and enhancing exsiting air paths; (b) creating new air paths; (c) reducing ground coverage, setting back building line alone narrow streets, aligning the long frontage of building with prevailing wind directions; and (d) maximising site greening upon development/redevelopment; 6 Intensification of use, adding building volume and/or ground coverage are not recommended unless with strong justifications and appropriate mitigation measures.
3.4 A GENERAL COMMENTARY AND NOTES OF THE UC-REMAP
A unique feature of the Hong Kong UC-ReMap is the extensive UCPZ 1 areas. These areas are natural areas and some are cool air production areas. Most of them are country parks under stringent control from further development. It is important that the urban climatic conditions be preserved. The UCPZ 2 areas are currently urban climatically ―netural‖ in terms of urban thermal comfort. They are mostly urban fringe or rural low land. It is important to maintain their urban climatic conditions.
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The UCPZ 3 areas can be found in the urban fringe or low-density development areas. Their urban climatic condition is ―moderately warm‖. As such some mitigation actions are encouraged where possible to mitigate the slightly negative climatic effect of these areas.
Isolated clusters of UCPZ 4 areas can be found in the new towns, including Tai Po, Ma On Shan, Yuen Long, Tin Shui Wai, and Tung Chung, etc. Care must be exercised to prevent aggravation of the problem. In addition, some of these areas currently benefit from the extensive green areas (UCPZ 1 & 2) and downhill air movements/valley winds around them. Such green areas and natural ventilation systems should be preserved.
Clusters of UCPZ 4 areas mixed with scattered UCPZ 5 areas can be found in various areas including Tseung Kwan O, Tuen Mun, Shatin, and Aberdeen etc. Currently, there are air paths and breezeways dividing the development clusters within these areas. They provide some useful air ventilation reliefs. However, some local areas may be subject to negative air ventilation condition, e.g. the air ventilation condition of Po Lam and Hang Hau areas in Tsuen Kwan O may be weakened due to the rather enclosed surrounding topography. At Tuen Mun, the area benefits from the north-south channeling winds. In particular, Tuen Mun River Channel is a useful breezeway into the town centre and it is important to maintain the openness of the channel.
Extensive arrays of inter-mixed UCPZ 4 & 5 areas can be found in the metro areas of Hong Kong at the northern part of the Hong Kong Island, at the Kowloon Peninsula and at Tsuen Wan. Not only are these areas extensive, they also form a continuous barrier to the beneficial sea breezes, particularly at the Kowloon Peninsula with its larger land masses. Therefore, mitigation measures are recommended and essential for these areas.
As shown in Figure I-125, the Hong Kong Urban Climatic Maps provide an urban climatic information platform and urban climatic planning framework with a comprehensive set of planning recommendations for strategic and district planning (Table I-43). It also provides an urban climatic context for site-level and area-wide further micro-climatic and AVA studies which urban climatologists should be consulted as and when necessary.
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Figure I-125 The UC-ReMap and Hong Kong Planning Framework
3.5 FOUR DESIGNATED AREAS
Based on the Hong Kong UC-ReMap, 4 Designated Areas can be identified (Figure I-126 and Table I-44). The designated areas are areas with clusters of UCPZ 5 surrounded by UCPZ 4 areas. They are areas of very high thermal load and poor dynamic potential. All the four Designated Areas are heavily built up areas with a mixture of residential, commercial and other land uses; and all four areas have narrow street networks, few open areas and green spaces and with intensive human activities. It is recommended to conduct focused and detailed studies of the 4 Designated Areas and to develop key mitigation plans for implementation. Section 3.1.2 can be a useful reference.
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Figure I-126 Four designated areas based on the HK UC-ReMap
Table I-44 Urban Climatic Analytical Characteristics of Four designated areas Urban Climatic Analytical characteristics Designated Building Ground Dynamic Vegetation Areas Main areas volume density Coverage potential % class (BVD) class (GC) class (DP) class Central + Area around The ≈ 4 and 5 ≈ 0 ≈ 0 ≈ 0 Sheung Wan + (high thermal (high ground (no positive Central (low DP) Sai Ying Pun capacity) roughness) benefit) Area around Causeway Bay + Causeway Bay MTR East Wan Chai ≈ 4 and 5 ≈ 0 ≈ 0 ≈ 0 station Area around Sha
Tsuen Wan Tsui Rd / Chung On ≈ 4 and 5 ≈ 0 ≈ 0 ≈ 0 St intersection Areas around Kwun Kwun Tong Tong MTR station ≈ 4 and 5 ≈ 0 ≈ 0 ≈ 0
3.5.1 Breezeways and air paths All 4 Designated Areas can benefit from breezeways (over 100m wide) and major air paths (width not less than 1/3 to 1/4 the average building height along the path) aligned to the prevailing winds (particularly summer wind). In Tokyo, the Kaze-no-michi (ventilation path) study from Tokyo Station to the waterfront has been a major initiative by the TMG to try establishing a major air path for the areas. This bold attempt requires determination and support from stakeholders and the general public. However, this is difficult to implement in
School of Architecture, CUHK Page 216 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT the Hong Kong context. As such, the focus should be on appropriately designed breezeways and air paths of sufficient width, which can improve the dynamic potential of an area by approximately 1 to 2 urban climatic classes, or more. This would in turn have an effect of lowering the UCPZ by 1 category.
3.5.2 Greening Greening has been strongly encouraged by TMG for their four designated areas in Tokyo‘s 23 wards. In the City of Stuttgart, green corridors leading into the city are zealously guarded and enhanced. For Hong Kong, developing a greening strategy to increase green coverage can be effective in enhancing human thermal comfort within the urban areas. Extensive road side tree planting, green podium, green wall and green roof, as well as water bodies and features at the pedestrian level are useful. Creating urban green oasis and establishing network of connected green corridors, ideally free of traffic, can provide resting points and more thermally comforting movement routes for pedestrians. Appropriately planned tree planting and good greenery coverage can reduce the thermal load of the urban environment by 1 to 2 urban climatic classes, or more. This, again, has the effect of lowering the UCPZ by 1 category.
3.5.3 Other mitigation measures – anthropogenic heat Reducing anthropogenic heat is useful, though not so effective in terms of mitigating urban thermal discomfort at the pedestrian level. Reducing surface traffic volume, pedestrianising a network of streets, enhanced tree planting, and adopting district cooling may contribute to improving urban climatic conditions. These have been attempted in Tokyo and elsewhere. TMG has adopted this mitigation measure with a more important national policy to reduce energy consumption of buildings. Hence, these mitigation measures have been championed mainly to support this national policy. However, it is estimated, based on recent researches in Japan, that the benefit to pedestrian level urban thermal environment is only less than half an urban climatic class. Nonetheless, it is still a potential minor improvement that is useful to bear in mind in the future.
3.5.4 Other mitigation measures – cool and water retentive materials Some overseas researchers have investigated the potential benefits using ‗cool materials‘ or ―water retention materials‖. Whilst this study is planning oriented and has not investigated the effect of using cool materials in details, it is worthwhile to further investigate cool and water retentive materials as a mitigation measure under separate studies.
3.5.5 Building Separation In line with 3.5.1, apart from creating breezeways and air paths, it is useful to increase urban permeability with building separations. Making reference to the Council for Sustainable
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Development's Invitation for Response Document titled ―Building Design to Foster a Quality and Sustainable Built Environment‖ under some circumstances, building separation (at all levels) equivalent to 20% to 33.3% of the total frontage area of the building is a useful reference and starting point in promoting air ventilation. Conducting detail AVA is also a useful way to establish the detail the separation requirement.
3.5.6 Some working examples of mitigation measures The following worked examples demonstrate ways to mitigate the adverse urban climatic conditions.
Example 1: A dense urban area has a very high FAR of 9 to 10, or higher. The area average ground coverage exceeds 70% with large podia typically at 100% site coverage. The area has little greenery. In this case, the area would fall under UCPZ 5, with very high thermal load and very low dynamic potential. It would induce very high heat related stress in the summer months.
Example 2: A dense urban area has a high FAR of 9 or 10. The area average site coverage can be limited to under 70%, and the area average greenery of 30% or more can be provided, the area would then fall under UCPZ 4. The area would have high thermal load and some dynamic potential. It would induce high heat related stress in the summer months of Hong Kong.
Example 3: Thus, for the two areas discussed above, it is beneficial to limit the area average building volume to FAR=7 or lower; to limit the area average site coverage to under 70%; and to ensure the area has an area average greenery of 30% or more. In doing so, the area would then fall in UCPZ of 3 to 4. Coupled with the possible benefits of the area‘s proximity to the waterfront, large open spaces and green hill slopes, a level of UCPZ 3 or even UCPZ 2 could be achieved. The area would have some thermal load and some dynamic potential. It would induce slight to moderate heat related stress in the summer months.
Given Hong Kong‘s high density city structure and building morphology, Examples 1 to 3 illustrate the importance of reducing ground coverage to create air paths and greenery to improve the urban climatic environment.
In existing dense urban areas, it is difficult to improve the urban climatic environment on an area average basis without lowering building density of the entire area. In UCPZ 4 and 5 dominated areas, for example in Sheung Wan and Causeway Bay, it is useful to have an ―area-line-point‖ planning strategy. Urban oasis can be strategically positioned to provide
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―point‖ of relief. Selected streets and open spaces could be aligned with the ―points‖ to create ―lines‖ of relief so that pedestrian has a choice to move around the city following the network of ―lines‖. An urban area so designed will have the needed environmental diversity important for urban thermal variations and options (Steemers & Steane, 2004).
Example 4: In suburban areas with a low FAR of 3, An area average ground coverage of 50%, and an area average greenery of 30% or more, the area would be classified as UCPZ 2. The area would have low/moderate thermal load and good dynamic potential. It would induce neutral or slightly negative heat related stress in the summer months.
3.5.7 Considering Building Volume Density [BVD], Ground Coverage, Greenery and Proximity of Openness There is no single solution to all urban climatic issues. Many other considerations and constraints have to be balanced before coming to a planning decision. Based on the UC- ReMap, appropriate planning parameters such as BVD, Ground Coverage, Greenery and Proximity to Openness could be ―targeted‖ to achieve a good balance. It is important to plan so that one stays within the threshold, which are explained above, of the respective UC-Map categories. For instance, if there is a need for higher building volumes/floor area ratio (FAR), then it is useful to offset it with further greenery and/or lower ground coverage.
BVD, Ground Coverage, Greenery and Proximity to Openness are ―first order‖ considerations in urban climatology. On top of that, the use of cool building materials, water retentive ground surface covering and water bodies, as well as reducing anthropogenic heat due to buildings and traffic can also help. Further and separate studies of these ―second order‖ benefits may be beneficial to complement the urban climatic understanding.
3.6 BEYOND THE FOUR DESIGNATED AREAS (FOCUSED AREAS)
Apart from the 4 designated areas identified, the Hong Kong UC-ReMap also highlights other ‗focused areas‘ that require care and attention. Although not as concentrated as the four designated areas in terms of UCPZ 5 areas, they are still high in thermal load and poor in dynamic potential with ―clustering of UCPZ class 4 and 5 areas‖ (Figure I-127):
Hong Kong Island Wan Chai / North Point / Quarry Bay and Shau Kei Wan areas
Kowloon Tsim Sha Tsui / Yau Ma Tei / Mong Kok / Sham Shui Po / Cheung Sha Wan/ Lai Chi Kok areas
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Hung Hom and To Kwa Wan / San Po Kong areas
NT Tuen Mun / Yuen Long areas
Mitigation strategies as explained in 3.5.1 to 3.5.7 above are applicable to these focused areas.
Figure I-127 Focused areas needing care and attention based on the HK UC-ReMap
3.7 LIMITATIONS AND CARE IN READING, INTERPRETING AND USING THE UC-REMAP
The UC-ReMap should be interpreted and applied appropriately and urban climatologist‘s assistance may be needed. For example, bearing in mind that the analysis was conducted on a 100m x 100m raster basis to gain an area-wide understanding of the urban climatic characteristics, it is inappropriate to scrutinise the map pixel by pixel, or to read into the fine boundaries of the pixels. Rather, the pattern, clustering and extent of the pixels (UCPZ) within the UC-ReMap will provide a better overview of the general urban climatic characteristics of an area.
For example, the extensive array of UCPZ 4 and 5 pixels in Mong Kok, Cheung Sha Wan and Sham Shiu Po inland area means that as a whole, mitigation actions are desirable and recommended in accordance with the planning recommendations of the UC-ReMap. Further detailed studies are needed.
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As for the extensive belt of UCPZ 1 and 2 areas south of the built up areas from Sai Ying Pun to Siu Sai Wan on the northern shore of Hong Kong Island, they provide an immediate buffer that benefits the built up areas to its north. It means that areas of UCPZ 1 that are immediately interfacing the UCPZ 4 and 5 areas are particularly important and should be preserved and enhanced.
Improving the urban climate of Hong Kong for quality living is one of the many important considerations towards sustainable development in Hong Kong. In planning terms, one must attempt to balance other important considerations and as far as possible synergise needs to achieve an optimised design.
3.8 STRATEGIC PLANNING IMPLICATIONS OF THE UC-REMAP
The UC-ReMap has the following strategic planning implications:
a. Planning Standards and Guidelines on urban climatic considerations The general urban climatic environment of Hong Kong, the identification of UCPZs and their planning implications/ recommendations can be consolidated for inclusion in the Hong Kong Planning Standards and Guidelines. This can provide an urban climatic planning framework for Hong Kong to guide the planning and development process, so as to ensure that appropriate urban climatic considerations are taken into account.
b. Guiding the planning and development process for future development areas The UC-ReMap provides a holistic urban climatic information platform for identifying urban climatic effects of major planning and development proposals, such as for new development areas. The UC-ReMap also provides an urban climatic planning framework to guide major feasibility studies.
c. Providing urban climatic based planning considerations for OZP review The UC-AnMap and UC-ReMap have strategically and comprehensively analysed the urban climatic conditions of Hong Kong, in forming a territorial-wide, urban climatic information platform for planners in support of their strategic and district level work. Appropriate planning actions could now be taken to improve the urban climatic conditions of the territory, particularly for the sensitive areas. The preparation and review of OZPs and the formulation of suitable planning parameters for different land use zones should take into account the UC-ReMap
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recommendations, as appropriate. The UC-ReMap also provides a framework of boundary conditions and background understanding to guide further detailed micro- climatic and AVA studies for individual sites.
3.9 UPDATING & MANAGEMENT
Taking into account the development cycle and changes in the urban structure of Hong Kong, it is recommended that the frequency in updating the UC-ReMap can be the same as the UC- AnMap, i.e. once every 5-6 years and scientific updating in every 10 years.
3.10 FUTURE WORK
The scientific field of urban climatology is advancing rapidly, especially in view of the recent World Climate Conference 3 at Geneva. The World Meteorological Organization (WMO) is increasingly emphasising the need for further scientific understanding in urban climatology. It is therefore prudent to treat the current work as ―a beginning‖ of on-going efforts by all parties to advance the urban climate understandings for Hong Kong. Like the Stuttgart experience, it is highly recommended that the Hong Kong SAR Government establishes an urban climate branch in one of its departments to continue the effort and to provide on-going and up-to-date information to enable better planning decision making.
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PART I(D): SUMMARY
1.1 BACKGROUND There is a shared vision to design cities that are sustainable, healthy, and comfortable for its inhabitants to enjoy. To achieve this, it is necessary to factor urban climatic considerations holistically and strategically into the planning process. Urban Climatic Map (UC-Map) is an information tool that presents features of urban climate relevant for planning, so that useful urban climatic information can be identified and utilised in the planning process.
There are typically two types of UC-Map widely used in practice: the Urban Climatic Analysis Map (UC-AnMap) and the Urban Climatic Planning Recommendation Map (UC-ReMap). In short, based on expert evaluation of available data, Thermal Load, Dynamic Potential and Wind Information are considered, synergised, and spatially mapped using a Geographical Information System (GIS) platform to form the UC-AnMap. Based on the analysis of useful meteorological, building, land use, topographical and vegetation information from the UC-AnMap and taking into account relevant planning considerations, the UC-ReMap could be developed. The UC-ReMap translates urban climatic understandings into planning guidelines and recommendations, which in turn facilitate planning actions and decision making.
1.2 DESKTOP STUDIES Three case studies have been conducted on the best practices of Stuttgart and Kassel in Germany and Tokyo in Japan. The key learning outcomes are as follow:
. UC-Map is a ―synthetic‖ and ―evaluative‖, as opposed to an ―analytic‖, understanding of the factors and parameters affecting the urban environment. It attempts to define climatopes, and to balance, prioritise and weigh the combined effects of the parameters appropriately in view of the nature of the planning decisions that need to be made.
. UC-Map is useful in assisting planning decision-making ranging from the regional scale of 1:100,000 to the urban scale of 1:5,000. UC-Map provides a holistic and strategic understanding upon which detailed and further site specific micro-scale studies could be identified and conducted.
. In Tokyo, the Thermal Environmental Map with an emphasis on Thermal Load was created in 2002 to ―highlight‖ the 4 problem areas of the city that the Tokyo
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Metropolitan Government could focus its policies, investigations and improvement actions. In Germany, with more than 30 years of experience, the study of UC-Map is more sophisticated and emphasises more on Dynamic Potential and also on Wind Information in evaluating wind directions and air paths.
. The working of the UC-Map is multi-disciplinary in nature. It works best with the concerted effort of different disciplines under the lead of the planning authority, and with full political backup of the government. Public awareness on climatic issues could be raised and participation should be encouraged.
. Once the UC-Map is created, the process of improving and updating the UC-Map is on-going in nature. Professional input is generally required to monitor the effectiveness of the application, collect further data for evaluation, refine the scientific basis as new knowledge develops, as well as to update the map to cope with changes of the urban morphology.
A summary of UC-Map studies around the world is also collated in Appendix 1.
1.3 STATE-OF-THE-ART OF UC-MAP Since the concept of UC-Map is well accepted by many German cities, the most authoritative references on the methodology for formulating UC-Map are the following German guidelines:
VDI-3787-Part 1 Environmental meteorology – climate and air pollution maps for cities and regions, 1997. and VDI-3787-Part 2 Environmental meteorology – methods for the human bio- meteorological evaluation of climate and air quality for urban and regional planning at regional level, 1998.
These two guidelines have established the symbols, representations, standards and expert recommendations in formulating UC-Maps. The two guidelines are widely adopted by UC- Map studies worldwide. Thus, they are important references for guiding the methodology of creating UC-Map for Hong Kong.
1.4 UC-ANMAP FOR HONG KONG The UC-Map is set at a scale of 1:5,000 in the context of Hong Kong, as the scale meets the requirement of the statutory Outline Zoning Plans (OZP). The UC-AnMap will be reported at 100m x 100m grid. With this resolution, climatopes patterns based on Thermal Load and
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Dynamic Potential of the urban morphology at a scale suitable for planning purposes could be referred to. Furthermore, appropriate wind information can also be inputed.
By focusing on intra-urban air temperature differences and air ventilation for the purpose of human urban thermal comfort, the UC-AnMap specifically deals with two urban climatic factors, Wind and Urban Thermal Comfort, which are particularly in relation to the Thermal Load, Dynamic Potential and Wind Information of the urban and natural environment.
Physiological Equivalent Temperature (PET) as a human urban thermal comfort indicator for synergising all relevant factors into the UC-AnMap will be used. Based on evaluation and calculation of the parameters, e.g. land use, building volume, green space, etc., the corresponding classification and the values of netural PET (nPET) could be defined. This allows a balanced consideration in formulating the UC-AnMap when the parameters are collated. In short, a 1 °C rise in air temperature approximates to 1 degree rise in PET. In turn, a 1 degree rise in PET can be mitigated by 0.5 m/s increase in wind velocity.
Hong Kong is located in the sub-tropical climatic zone with hot summer months and mild winter months. Based on the technical input of outdoor thermal comfort study of Hong Kong, it can be established that at the typical summer air temperature of around 28 °C, over 75% of the people surveyed will report a thermal sensation of warm, hot and too hot. Whereas at the typical winter temperature of 15 °C, less than 21% reports a thermal sensation of slightly cold and only 2% reports cold. Hence, for urban thermal comfort, the problems in Hong Kong are confined to the hot and humid summer months – June, July and August. For this reason, a UC-Map of summer conditions is the most important as far as wind and urban thermal comfort is concerned.
1.5 METHODOLOGICAL BASIS OF UC-ANMAP Input data are obtained from the Planning Department and the Hong Kong Observatory. GIS has been employed to structure the information. The software, ArcMap, is used as the platform of the UC-AnMap study.
With reference to the German‘s guideline VDI 3787 Part 1 1997 and through evaluating Hong Kong‘s unique urban morphology, a refined methodology for formulating UC-Map for Hong Kong has been established.
It is important to create the initial UC-AnMap based on a ―frozen‖ timeframe, which has been set at 2009 in this study. On this basis, future updating of the map‘s timeframe is relatively easy when newer building information, becomes available.
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The urban climate of the city could be characterised by a balanced consideration of the positive and negative effects on Thermal Load and Dynamic Potential – both due to the urban morphology and surface characteristics. To this end, a number of information layers have been assembled (Table I-45). These layers of data form the basis for the eventual production of the UC-AnMap. The classification values for each layer are basically a numerical assignment (i.e. positively and negatively) of the parameter‘s likely effects on the PET value. When the classification values are collectively considered, the draft UC-AnMap could be generated. The Wind Information Layer is then added to the draft UC-AnMap to generate the final UC-AnMap. This allows air paths and air mass exchanges to be identified. The collated and synergised information contained in the final UC-AnMap will be used for preparing the UC-ReMap later.
Table I-45 Descriptions of the layers of the UC-AnMap
Physical Criterion Effect Scientific Basis Input layers
Layer 1 Negative Building bulk Building Volume Map Layer 2 Thermal Load Altitude and Elevation Topographical Height Map Positive Layer 3 Bioclimatic effects Green Space Map Layer 4 Negative Urban permeability Ground Coverage Map
Bioclimatic effects Layer 5 Dynamic Potential - Cold air movement Natural Landscape Map Positive Air mass exchange and Layer 6 Neighbourhood effects Proximity to Openness Map
Layer 7 MM5 simulaiton and Wind Information - Prevailing Wind Directions HKO field measurements (Summer)
1.6 DESKTOP STUDIES ON WIND DATA Through desktop studies of the German Guideline [VDI3787-Part1], together with case studies of wind information used in the making of Stuttgart UC-Map and Tokyo Thermal Environmental Map, the following lessons have been identified:
Wind data is typically collated from observatory data – especially stations in the city. Model simulated data can be used to supplement this.
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For planning purposes, the collated wind data are expertly evaluated taking into account topography, land use, water body and greenery understanding of the city and its surrounding areas.
For urban air ventilation, the background wind, localised land and sea breezes, topography-affected channeling and valley winds, cold air production, cool air drainage and downhill air movement, where appropriate are expertly evaluated.
Key (prevailing) wind directions, air circulations and ventilation areas are then coded onto the wind information layer of the Urban Climatic Analysis Map (UC-AnMap).
1.7 WIND INFORMATION LAYER FOR HONG KONG The wind information layer is part of the UC-AnMap for Hong Kong. It should not be used for any other purposes including site specific AVA studies.
The UC-AnMap study for Hong Kong is based primarily on long term wind data of 40 HKO stations around Hong Kong, and supplemented with HKUST‘s MM5/CALMET 2004 model wind simulations at 60m above ground level (roughly the areal average building height of urban Hong Kong). Topography, greenery and ground roughness information are also referred to when the data are evaluated.
The important wind data for the summer months (June-August) of is coded onto the GIS based UC-AnMap of Hong Kong. This forms the spatial information basis of expert evaluation.
Based on literature review, observatory and modelling data, the team led by Professor Lutz Katzschner has expertly evaluated the information and summarised their findings. For Hong Kong, different wind sources including the background wind, channeling effects due to topography, the localised land and sea breezes, as well as the downhill air movements are identified. Areas of similar characteristics are grouped into zones. The expertly evaluated wind information layer (Figure I-128) is prepared.
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Figure I-128 Wind Information Layer – Prevailing Wind Directions (Summer)
1.8 FINAL URBAN CLIMATIC ANALYSIS MAP FOR HONG KONG Based on the 6 layers and the consideration of the positive and negative effects of Thermal Load and Dynamic Potential, 8 urban climatic zones (climatopes) can be categorised. The description of the 8 urban climatic classes is shown in Table I-46.
Table I-46 Descriptions of the 8 urban climatic classes of the UC-AnMap
Urban Climatic Class Impact on Thermal Comfort
Moderately negative Thermal Load and 1 Good Dynamic Potential ●● Moderate Cooling
Slightly negative Thermal Load and Good 2 Dynamic Potential ● Slight Cooling
Low Thermal Load and Good Dynamic 3 Potential - Neutral
Some Thermal Load and Some Dynamic 4 ● Slight Warming Potential
Moderate Thermal Load and Some 5 ●● Moderate Warming Dynamic Potential
Moderately High Thermal Load and Low 6 ●●● ModeratelyStrong Warming Dynamic Potential
High Thermal Load and Low Dynamic 7 ●●●● Strong Warming Potential
Very Highly Thermal Load and 8 ●●●●● Very strong Warming Low Dynamic Potential
Through incorporating the Wind Information Layer, the final UC-AnMap for Hong Kong is produced (Figure I-129).
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Figure I-129 The Final UC-AnMap of Hong Kong with Wind Information Layer – Prevailing Wind Directions (Summer)
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1.9 BACKGROUND AND PURPOSE OF URBAN CLIMATIC PLANNING RECOMMENDATION MAP Based on the UC-AnMap, the UC-ReMap and key planning recommendations for its Urban Climatic Planning Zones could be formulated. The UC-ReMap of Hong Kong is planning action oriented. It provides an urban climatic information platform and planning framework upon which urban climatic considerations can be taken into account at the strategic and district planning levels.
1.10 OVERSEAS EXPERIENCE OF UC-REMAP AND KEY LESSONS LEARNT
Figure I-130 Two examples of UC-ReMaps: Stuttgart and Tokyo (right)
The German Guideline VDI3787-Part 1 has been referenced and two case studies (the City of Stuttgart and the Metropolitan Areas of Tokyo [Figure I-130]) have been conducted. The lessons learnt are as follow: . The UC-AnMap provides a platform of urban climatic information. . The UC-ReMap provides an urban climatic based planning framework typically at the city and district levels. . The UC-ReMap provides planning recommendations based on an evaluation of a number of planning parameters. . The UC-ReMap identifies problem areas and climatically sensitive areas that are in need of attention. . The UC-ReMap focuses on improving urban climatic conditions and mitigating UHI effect to improve outdoor thermal comfort thus living quality. . The UC-ReMap itself is not a regulatory instrument.
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1.11 KEY PARAMETRIC UNDERSTANDING OF URBAN CLIMATE RELATED PLANNING PARAMETERS FOR RECOMMENDATIONS There are 6 data layers in formulating the UC-AnMap, namely building volume, topographical height, green space, ground coverage, natural landscape, and proximity to openness. Among the six layers, while topographical height and natural landscape can be taken as given, building volume, green space, ground coverage and proximity to openness are useful parameters for planning considerations. The key parametric understanding of implications of the four parameters (on an area average basis and based on the UC-AnMap understanding), can be summarised below.
1.11.1 Building Volume: (a) In contrast to plot ratio, the concept of Floor Area Ratio (FAR), which counts for all above ground floor area including concessionary Ground Floor Area, is practically and realistically more in line with building volume and hence the thermal load understanding of the UC-AnMap. Reducing/maintaining Building Volume in low/medium density areas with FAR26 of 1 to 5 is very effective and beneficial to lowering Thermal Load . (b) In medium/high density areas, FAR in the range of 6 to 7 can be suggested as ―reasonably optimal‖ when developments are carefully designed. FAR of 8 to 9 is occasionally possible subject to provision of effective mitigation measures. (c) In very high density areas, a FAR higher than 10 will increase the Thermal Load significantly, therefore, careful scrutiny of building volume is essential and mitigation measures are needed. (d) To limit the increase in thermal load due to building volume, it is recommended that FAR of 7 be adopted as the threshold from the outset, subject to consideration of other relevant factors. (e) In the urban context of Hong Kong, unless FAR can be dramatically reduced, other mitigation measures such as improving air paths, reducing ground coverage and increasing green spaces are necessary to complement the control on building volume and building height. (f) With regard to building height - It is effective to enhance air ventilation by controlling building heights in low/medium density areas with building height/street width ratio (H/W) of 2 and below;
26 Floor Area Ratio (FAR) of the Urban Climatic Map at 100m x 100m grid is the ratio between the total above ground floor area of all the buildings over the buildable area.
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In general, varying building heights is useful to enhance Dynamic Potential. For urban areas with H/W of 2 or above, non-uniform building height bands of sufficient height contrast would be more effective to enhance air ventilation. Other parallel measures such as providing air paths should be considered as well to enhance effectiveness; Increase in floor-to-floor height will increase the building volume and thus the Thermal Load. Therefore, unreasonably high floor-to-floor height is not encouraged.
1.11.2 Greenery: (a) Based on CUHK‘s in-house research of model simulation parametric study using ENVI-Met model simulation, a city area average of 30% or more greenery coverage (at ground, podium, and low level rooftop) and preferably with tree planting, is effective to reducing thermal load.27 (b) Pockets of green oasis (large area of tree planting in urban areas) are useful in providing localised thermal relief to the urban environment.
1.11.3 Ground Coverage: (a) Reducing Ground Coverage 28 of an area is an effective way to improve wind penetration and thus the dynamic potential. In urban areas, given that a Ground Coverage of below 50% will result in a 1 degree decrease in PET, and assuming that the Building Site Area 29 Ratio is 70%, it is recommended to reduce site ground coverage of to 65% or less.
1.11.4 Proximity to Openness and Connectivity: (a) Properly orientated air paths connecting to the waterfront or open spaces are effective in bringing air ventilation into the city. ‗Green fingers‘ from vegetated hill slopes into the urban areas are also useful planning features.
27 The CUHK study finding (Wang & Ng. 2010) is in line with Sustainable Development Council‘s recent engagement exercise titled Building Design to Foster Quality and Sustainable Built Environment that recommended site greening of 20 to 25%; this is equivalent to 33 to 37% when it is normalised to the ―city area average understanding‖ of the UCMap. Japanese researcher Professor Masakazu Moriyama has also recently obtained similar findings with his research in greening based in Osaka.
28 Ground Coverage is the total footprint of buildings of a 100m x 100m UCMap grid. Hence Ground Coverage Ratio is the ground coverage over the total area of the 100m x 100m grid.
29 Building Site Area includes all land use zones, including Residential, Commercial, Industrial, Government, Institution & Community Facilities, and Other Urban or Built-up Land, that can be built upon.
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(b) A permeability of 25 to 35% is normally suggested.30 This can be achieved with an aggregate of roads leading from the waterfront, open spaces, non-building areas, and gaps between buildings etc. The key for urban permeability is to relate it with air ventilation connectivity, that is to say, the open spaces and air paths must be connected.
1.12 A COMPARISON OF RECOMMENDATIONS The Council for Sustainable Development‘s (SDC) public engagement exercise titled ―Building Design to Foster a Quality and Sustainable Built Environment‖ contains a number of suggestions, which have been compared with the findings of this study (Table I-47). While the policy options set out by the SDC in its ―Invitation for Response‖ document are more related to individual building sites, recommendations in this Study are area-averaged and district-based, and derived from a strategic and comprehensive analysis of the urban climatic conditions of Hong Kong as a whole. However, they largely complement one another.
Table I-47 Suggestions of UC-Map vs. SDC’s exercise Site based measures General Planning Guidelines suggested in SDC’s Recommended under the UCM IR Document Study31
● building separation requirement for the Building Separation/ 20% to 33.3% building middle and high assessment zones as per Building Setback separation & set back at PNAP APP-152 street level in narrow ● building setback; Ground Site Coverage streets ● Reduce ground coverage to not more than 65%. ● Greenery (preferably tree planting) of no Greenery less than 30% for sites larger than 1 ha, 20% to 30% of the site and 20% for sites below 1 ha at lower areas levels, preferably at grade. Sites smaller than 1,000m² are exempted.
30 Refer to the Final Report of Buildings Department‘s Study [BA/01/2006] on Building Design that Supports Sustainable Urban Living Space in HK, Jan 2009. The study was based on CFD parametric studies by the consultant. 31 The General planning guidelines recommended under the UCM Study are derived based on the urban climatic considerations at strategic/district levels. Since they are developed using the area average 100m ×100m grid understanding of the UC-Map and assuming urban homogeneity, they are intended to be district-based measures and not supposed to explain the micro scale details. The numbers suggested are not to be directly adopted for site-based works. In determining appropriate development parameters for individual sites, apart from these general planning guidelines, reference should also be made to all strategic and district planning frameworks as well as individual site circumstances.
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● City area average threshold FAR values Building Reviewing prevailing of 3 to 7 are suggested; policies for granting GFA Volume/Capping GFA ● FAR > 7 needs some mitigation concessions, including Concession measures; introduction of overall / individual caps ● FAR > 10 to be very carefully scrutinised and mitigated. Building permeablility (at Proximity to Openness all levels of the building) ● Air paths and Green fingers; and Connectivity equivalent to 20% to ● Air path connectivity. 33.3% of total frontal area in large sites. Building Heights ● Vary building heights; Nil ● Excessive floor to floor height is not encouraged.
1.13 THE UC-REMAP FOR HONG KONG Five urban climatic planning zones are defined within the UC-ReMap (Figure I-131). Their respective key planning recommendations have also been formulated (Table I-48).
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The Urban Climatic Planning Recommendation Map of Hong Kong 100m x 100m resolution, raster based
Figure I-131 The UC-ReMap, 100m×100m raster based, with wind information layer – prevailing wind directions (summer)
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Table I-48 The 5 urban climatic planning zones of the UC-ReMap Impact on Thermal Urban Climatic Planning Strategic planning No Urban Climatic Class Comfort Zone (UCPZ) action ●● 1 Moderate Negative Thermal Load and Good Dynamic Potential Moderate cooling UCPZ 1 Preservation ● Urban climatically valuable 2 Some Negative Thermal Load and Good Dynamic Potential Slight cooling area - 3 Low Thermal Load and Good Dynamic Potential Neutral UCPZ 2 Maintenance ● Neutral urban climatically 4 Some Thermal Load and Some Dynamic Potential Slight warming sensitive area
●● Some mitigation Moderate Thermal Load and Some UCPZ 3 actions 5 Moderate Dynamic Potential Moderate urban climatically encouraged where warming sensitive area possible ●●● 6 Moderately High Thermal Load and Moderately strong Low Dynamic Potential UCPZ 4 Mitigation actions warming High urban climatically recommended and ●●●● necessary 7 High Thermal Load and Low sensitive area Dynamic Potential Strong warming ●●●●● Mitigation actions Very High Thermal Load and Low UCPZ 5 recommended and 8 Dynamic Potential Very strong Very highly urban warming climatically sensitive area essential ● cooling thermal impact ● warming thermal impact
In addition to the depiction of UCPZs, a set of general recommendations that are useful for reference in the planning process has been prepared32 as part of the UC-ReMap.
1.14 URBAN CLIMATIC MAPS AND HONG KONG PLANNING FRAMEWORK The UC-Maps for Hong Kong provide information for strategic and district planning (Figure I-132). It also provides, for reference if needed, the urban climatic contextual information for site-/area-wide micro-climatic and AVA studies. The UC-ReMap (Figure I-131) can be included in the Hong Kong Planning Standards and Guidelines to guide the strategic and district planning process.
32 As in Table I-43
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Figure I-132 UC-Map and Hong Kong Planning Framework
1.15 LIMITATIONS AND CARE IN READING, INTERPRETING AND USING THE UC-REMAP Urban climate is a complicated subject that is relatively new in Hong Kong. Based on German and Japanese experience and practice, it is very important that the UC-ReMap and its recommendations and advices be read and interpreted appropriately, and that urban climatologists be consulted if and when necessary.
Although the UC-ReMap of Hong Kong is assembled based on a 100x100m grid, the map should not be read pixel by pixel. Rather, the pattern, clustering and extent of the pixels (UCPZ) give a better understanding of the general characteristics of an area/district. The map should not be used literally for site specific reference and application.
Improving the urban climate of Hong Kong for quality living is only one of the many considerations towards sustainable development in Hong Kong. In planning, one must attempt to balance other important considerations and, as far as possible, synergise needs to achieve an optimised design.
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1.16 UPDATING STRATEGY The UC-Map created in this study has the frozen timeframe for the year 2009, however, it is designed so that it could be conveniently updated as the map is created in GIS layer format. Where new developments have to be taken into consideration, the up-to-date version of the map could be easily produced by updating the specific layer.
. Building geometry and urban morphology For the sake of rapid urban developments, the files used in the Land Use Map layer such as, building shape file and podium shape file as well as Digital Elevation Model (DEM) raster files are advised to be updated every 5 to 6 years. Taking into account the development cycle and the change in urban structure of Hong Kong, the frequency of updating the UC-AnMap and UC-ReMap can be once every 5-6 years.
. Scientific development The scientific understanding and technologies in this field is constantly evolving. To enhance the UC-Maps, it is recommended that scientific updating of the UC-AnMap and UC-ReMap should be conducted at roughly 10 year intervals to accommodate for new climatic knowledge in the field.
1.17 FUTURE WORK The scientific field of urban climatology is advancing rapidly, especially in view of the recent World Climate Conference 3 at Geneva. The World Meteorological Organization (WMO) is placing increasing emphasis on further scientific understanding on urban climatology. It is therefore prudent to treat the current work as a beginning of the on-going efforts by all parties. It is also highly recommended that the Hong Kong SAR Government establishes an urban climate branch in one of its departments, similar to the Stuttgart counterpart, to continue the current effort, and to provide on-going and up-to-date information to facilitate better planning decision making.
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PART I: APPENDICES
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APPENDIX 1: SELECTED UC-MAP STUDIES AROUND THE WORLD
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APPENDIX 2: AN EXAMPLE OF DATA PROVIDED BY HKO – WIND SPEEDS AND DIRECTIONS BY MONTH OF THE 40 HKO STATIONS FOR THE STUDY
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APPENDIX 3: AN EXAMPLE OF DATA PROVIDED BY HKO – WIND SPEEDS AND DIRECTIONS BY HOUR (JANUARY) OF THE 40 HKO STATIONS FOR THE STUDY
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APPENDIX 4: TWO EXAMPLES OF WIND ROSES BY HKO
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APPENDIX 5: EXPERT EVALUATION ON SEA AND LAND BREEZES OF HONG KONG DURING DAY TIME AND NIGHT TIME RESPECTIVELY
Evaluated Sea Breezes, after (Zhang & Zhang, 1997)
Evaluated Land Breezes, after(Zhang & Zhang, 1997)
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APPENDIX 6: A COMPARATIVE STUDY OF SELECTED HKO OBSERVED AND MM5/CALMET MODEL WIND ROSES – SUMMER (JUN-AUG)
(Courtesy Prof Jimmy Fung, HKUST)
Also refer to: Yim, S. H. L., J. C. H. Fung, A. K. H. Lau, & S. C. Ko (Holmer). Developing a high-resolution wind map for a complex terrain with a coupled MM5/CALMET system. Journal of Geophysical Research, 112, 1-15 Yim S. H., Fung J. C., Lau A. K. Mesoscale Simulation of Year-to-Year Variation of Wind Power Potential over Southern China. Energies. 2009; 2(2):340-361
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APPENDIX 7: A COMPARATIVE STUDY OF SELECTED HKO OBSERVED AND MM5/CALMET MODEL WIND ROSES – ANNUAL (Courtesy Prof Jimmy Fung, HKUST)
Also refer to: Yim, S. H. L., J. C. H. Fung, A. K. H. Lau, & S. C. Ko (Holmer). Developing a high-resolution wind map for a complex terrain with a coupled MM5/CALMET system. Journal of Geophysical Research, 112, 1-15 Yim S. H., Fung J. C., Lau A. K. Mesoscale Simulation of Year-to-Year Variation of Wind Power Potential over Southern China. Energies. 2009; 2(2):340-361
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APPENDIX 8: THE RELATIONSHIP BETWEEN BUILDING VOLUME DENSITY (%) AND FLOOR AREA RATIO
1) (2) (3) (4)
UC- Building =[(2) x Floor Area Ratio (FAR) 2 AnMap volume 1.217 = [(3) x Approximate Floor Area (m )]/ [grid (5) 2 Building density million m3 (m ) x BSAR] Volume (BVD) % /fl.ht.(m)]/ Plot Ratio Layer Approxim =(4) / (FAR/PR) - PET ate Floor categori Area (m2) es In UC Assume AnMap, approximat BVD= e floor area 2 100%, Its = 1000 m value Assume average building site area (Building Site BSAR=50%, BSAR=55%, BSAR=60%, BSAR=65%, BSAR=70%, =1.217 2 Assume Area) to 100x100 grid ratio of … in an 1 km Assume Assume Assume Assume Assume million m3 fl.ht. =3 to urban area BSAR (%) FAR/PR of FAR/PR of FAR/PR of FAR/PR of FAR/PR of 4m BSAR BSAR BSAR BSAR BSAR 1.2 1.5 1.2 1.5 1.2 1.5 1.2 1.5 1.2 1.5 50% 55% 60% 65% 70%
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 and 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paved ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to 2 0 to 4% ~ to 12-16 2.4-3.2 2.2-3.0 2.0-2.7 1.8-2.5 1.7-2.3 2.0-2.7 1.6-2.2 1.8-2.5 1.5-2.0 1.7-2.3 1.3-1.8 1.5-2.1 1.2-1.7 1.4-1.9 1.1-1.5 ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to 3 4 to 10% ~ to 30-40 6.1-8.1 5.5-7.3 5.1-6.8 4.6-6.2 4.3-5.7 5.1-6.8 4.1-5.4 4.5-6.1 3.6-4.8 4.3-5.7 3.4-4.5 3.8-5.1 3.1-4.1 3.6-4.8 2.9-3.9 ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to ~ to 4 10 to 25% ~ to 75-100 15.2-20.3 13.6-18.2 12.7-16.9 11.5-15.4 10.9-14.5 12.7-16.9 10.1-13.5 11.4-15.2 9.1-12.1 10.6-14.1 8.5-11.3 9.6-12.8 7.7-10.3 9.1-12.1 7.3-9.7 > > > > > > > > > > > > > > > 5 25 to 100% > 75-100 15.2-20.3 13.6-18.2 12.7-16.9 11.5-15.4 10.9-14.5 12.7-16.9 10.1-13.5 11.4-15.2 9.1-12.1 10.6-14.1 8.5-11.3 9.6-12.8 7.7-10.3 9.1-12.1 7.3-9.7
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PART II: WIND TUNNEL BENCHMARKING STUDIES
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PART II(A): METHODOLOGY OF AREA SELECTION FOR BENCHMARKING
PART II(A)-1 PURPOSE The focus is to explain the methodology and rationale for site selection of benchmarking areas of the study. The areas should give a good ―representation‖ of existing pedestrian level wind environments of urban Hong Kong. A total of 20 study areas have been selected.
PART II(A)-2 INTRODUCTION
For example: In Japan, research studies have indicated that a Velocity Ratio (VR) of 0.2 to 0.4 is achievable in wider streets, and a VR of 0.1 to 0.2 can be expected in narrower streets. But building height to street width ratio in Japan is much lower. What are the ranges of VR that Hong Kong’s streets and spaces could expect?
It is important to understand the existing pedestrian wind environment so as to establish the current situations, for instance, the range of velocity ratios and wind speeds that a high density urban environment like Hong Kong can provide. It is also possible to pin-point the problem areas and favourable site conditions, quantitatively, so as to facilitate better planning and design in the future. In short, the exercise can provide the much needed quantitative data to further advance the AVA methodology.
A key requirement of the study is to establish a pedestrian level wind standard for thermal comfort in the urban areas of Hong Kong. An important step in any research study is to critically examine the ―current‖ condition, in other words, taking a ―snapshot‖ of the existing conditions. Through benchmarking the existing conditions, this help addresses the initial question on the magnitudes, ranges and characteristics of wind velocity ratios (VRw) and wind speeds that one could typically expect in urban Hong Kong. With this information on the existing conditions, further questions could be formulated and answered. Separately, making use of the benchmarking results, others could collate the data for their own use.
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Benchmarking is not a new concept, and it should not be confused with other studies with a design or development purpose in mind. The core focus of benchmarking studies is to capture the existing conditions rather than a speculation of future scenarios.
PART II(A)-3 OBJECTIVE The main objective of the benchmarking studies is to establish some typical existing representative pedestrian wind conditions of Hong Kong based on the current urban morphology. The data generated may then be used for further studies and investigations.
For this study, benchmarking is basically a representative ―snapshot‖ of Hong Kong‘s pedestrian wind environment.
PART II(A)-4 METHODOLOGY A number of parameters can affect the wind environment on ground level, which can be broadly divided into the following key categories: Climatic and wind Topographical and Exposures Urban Morphological
4.1 CLIMATIC AND WIND PARAMETERS Unlike most other countries, Hong Kong is relatively small in territorial terms. Hong Kong is within one climatic region, and for the purpose of urban design and planning, there is little need for the study area to consider ―regional‖ differences in terms of climatic conditions (e.g. temperature).
However, the topography of Hong Kong is complex. The resultant winds, taking into account the surrounding topographies, can vary for different study areas. A good understanding could be drawn from the Hong Kong Observatory‘s (HKO) station data (see Figure II-1).
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Figure II-1 Locations of Hong Kong Observatory weather stations
The HKO reports annual wind roses of their stations in their ―annual summary of meteorological observations in Hong Kong‖.
For the purpose of this Study (i.e. urban pedestrian wind environment), it is important to first detect and distinguish a main wind rose characteristic, i.e. whether there is a strong prevailing wind condition. Referring to HKO‘s summary data of recent years, it could be concluded that areas in Hong Kong do exhibit the characteristics of ―with‖ and ‗without‖ a strong prevailing wind conditions. EPD‘s MM5 simulated wind data on the Planning Department‘s website gives a similar impression. The differences will need to be factored into the site selection considerations.
Secondly, it is useful to examine, again based on HKO‘s data, if there are ―strong‖ or ―weak‘ urban wind conditions. Very few HKO stations are in the urban area and within the urban canopy layer (UCL). (Figure II-2) (Urban canopy layer height can be defined as the mean roof height of the urban area.) Examining the few HKO stations that are within the UCL, it could be concluded that they are similar with a mean annual wind speed of some 2.5 m/s or around 9 km/hr (incidentally, this is roughly a third of Waglan Island‘s mean wind speed data). At the UCL level, the wind environment of different areas in Hong Kong, in terms of wind speeds, do not differ significantly for the purpose of this Study.
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Figure II-2 Mean wind speed (kilometer/hour) of HKO stations 2005. (The highlighted stations are HKO stations that are in the urban area and within the UCL. Left column: prevailing wind direction of the site, in degree clockwise from north); Right column: the 10-minute-mean wind speed of the year (km/hr))
In addition, by separately examining EPD‘s MM5 data at V infinity level of the entire territory of Hong Kong, in terms of wind speeds, a similar conclusion could be drawn. From both the HKO data and the V infinity level data from EPD‘s MM5 simulation, it could be noted that the wind speeds within different urban areas of Hong Kong do not differ significantly.
4.2 TOPOGRAPHICAL AND EXPOSURES PARAMETERS For the purpose of air ventilation assessment (AVA), the complicated thermal effects of wind (including anabatic* and katabatic** wind) will not be considered. The purpose of AVA is to guide better design and planning. It predominantly considers how the bulk of the buildings affect the prevailing or channelled (―mechanical‖) wind. Some considerations of how nearby topographical features accelerate or modify the ―mechanical wind‖ are useful. Areas on slope or near hills should be considered. Currently, the AVA methodology takes the ―mechanical wind‖ as the main driving wind. The thermal induced wind is a lot more complicated to account for without the availability of measured local wind data. Further versions of the AVA methodology might attempt to improve the results.
* anabatic wind local air current that blows up a hill or mountain slope facing the Sun ** katabatic wind wind that blows down a topographic incline such as a hill or mountain
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There are basically two types of area exposure conditions, including areas surrounded by other buildings, and areas with an open exposure to the sea or to large open spaces. For the latter areas, the approaching wind profiles are typically simple and follow the log law. One could also expect higher wind speeds, and better VRw. For area surrounded by buildings, the approaching wind are typically weakened and lower VRs are expected. Flows are also more turbulent (Figure II-3). The understanding provided in Figure II-3 also applies to ―high topographical features‖.
Figure II-3 Wind profiles modified by the building block. [left] wind profile from water or large open space typically follows the log law. [middle] buildings modifies the profile. [right] a “displacement height” results to the wind profile. Wind speeds below the displacement height are reduced. This height is generally assumed to be the mean roof height of buildings.
4.3 URBAN MORPHOLOGICAL PARAMETERS For the study, the geometric and morphological parameters of the urban environment are the most important factors to consider. Pedestrian wind is largely determined by a number of urban features, including: Ground Coverage Street Grid Patterns and Orientations Building Height to Street Width Ratio (H/W Ratio) Building Heights and Building Height Variations Building Geometries Elevated Structures
4.3.1 Ground Coverage Based on scientific results in different studies, ground coverage of buildings have a major impact to pedestrian level wind. (Figure II-4)
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Figure II-4 Ground coverage and wind velocity ratio of 2 areas in Japan (Case 16 has higher building ground coverage than Case 19)
It was established in the earlier ―Feasibility Study for Establishment of AVA System‖ that permeability is important at the level where the benefits are needed. For pedestrian level wind, ground level permeability is beneficial. This means lower ground coverage. (Figure II-5)
Figure II-5 Ground coverage and wind velocity ratio of Mongkok, as compared with other cities in Japan (Courtesy Wind Engineering Research Center, Tokyo Polytechnic University, Japan)
As such, it is useful to select the benchmarking areas in Hong Kong with a variety of building ground coverage.
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4.3.2 Street Grid Patterns and Orientations Streets that align within +/-30 degrees of the wind direction have significantly better wind ventilation than streets perpendicular to it (Figure II-6). The difference could be substantially depending on the heights of the flanking buildings. It is therefore useful to select the benchmarking areas with streets both parallel and perpendicular to the incoming wind.
In addition, it is useful to select study areas with different street patterns, as regular street patterns have the potential of channeling wind along the streets, whilst irregular street patterns are more limited in this respect (Figure II-7). On the other hand, irregular streets could have lower canyon effects as fewer streets would be perpendicular to the wind. Depending on the wind direction and the layout of the irregular streets, there could be a potential of a ―wind network‖.
In short, regular streets have the potentials of both stronger channeling wind and weaker canyon winds, whereas irregular streets have lesser extremes of both.
Figure II-6 Streets parallel to the incoming wind “channels” the wind through it effectively
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Figure II-7 Wind flow patterns and regimes with regular streets and irregular streets
Channeling – When streets are parallel to the incoming wind, the streets will “channel” the wind through it. Provided the street is within +/- 30 degrees from the incoming wind direction, the channeling is effective and there is little reduction of wind speed along the street.
Canyon – When streets are perpendicular (or more than +/- 30 degrees) to the incoming wind and surrounded by buildings on both sides, the streets will behave like canyons. Wind flowing through it will behave depending on the ratios of the canyon (see Figure II-8). A H/W ratio of 1.5:1 and more could be considered as canyons (refer to Figure II-10).
Channeling Canyon Figure II-8 Diagrams showing channeling and canyon wind flows
Street grid patterns, as defined by, say, roads and paths, do not necessarily dictate the wind pattern. Fundamentally, it is not about how the streets are laid out, but how the buildings are laid out as they are the tangible objects blocking and modifying the wind pattern. The layout of internal spaces and disposition of buildings would ultimately affect pedestrian wind environment.
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For example, there are 2 building estates with the same internal ―streets‖ (Figure II-9), the layout on the left could be regarded as having a regular development layout, whereas the layout on the right has an irregular pattern. Therefore, they would be categorised as such for the area selection process.
Figure II-9 Building dispositions and internal streets can create different patterns of urban morphology even if the streets are “regular”
4.3.3 Building Height to Street Width Ratio (H/W Ratio) Scientifically, there are three regimes of wind flow (Figure II-10) within the urban environment, the characteristics of which are mostly related to the Building Height to Street Width Ratio (H/W Ratio): Isolated roughness flow Wake interference flow Skimming flow
For example (Figure II-10 [orange circle]), for a street with long terraced buildings on both sides (where L is large), when height of buildings is 20m, and width of street is 10m, then H/W Ratio is 2. The wind would be classified as ―skimming flow‖, as if it was a canyon [orange circle].
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Figure II-10 Flow characteristics over urban forms (H=height of the blocks, W=width of the gap in between the rows of blocks, L=length of the blocks)
While all three wind flow regimes could be represented in Hong Kong, most flow characteristics in the dense urban areas will be ―skimming flow‖ with vortexes inside the street canyons. In some deep canyons, double-vortex might exist.
Isolated roughness flow could typically be found in areas with very wide streets and a H/W Ratio of 1:2 or less. Wake interference flow could be found where H/W is around 1:1.5. Skimming flow could be found where H/W is around 1.5:1 or more. In Hong Kong, H/W Ratio of 3:1, 5:1, 10:1 or worse could be found. When benchmarking, various H/W ratios will be represented in the study.
4.3.4 Building Heights and Building Height Variations The relationship of building heights and street widths would have a bearing on wind flow as in Figure II-11. Building height variation could potentially create differentials in wind pressures and thus promote horizontal air movements. In addition, downwash effects are well-known wind phenomenon. In Hong Kong the two effects are common and should be represented. Therefore, it is useful to have study areas that include regular building height arrays, irregular building height arrays; as well as areas with large building height differences and areas with little differences.
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Figure II-11 Flow characteristics over urban forms
4.3.5 Building Geometries Wind flows around various built forms are different (e.g. streamline, circular and bluff). Most buildings in Hong Kong are point blocks or slab blocks (i.e. bluff bodies – rectangular and/or with shaped edges and corners), and this is the most important to represent.
It is useful to understand building geometries based on their impermeability to wind. The heights and widths of buildings have determining effects on the wind flows, particularly at the wake regions behind the buildings. In Hong Kong, most buildings are tall. The building height effect to pedestrian level wind is therefore significant. The width of the building could be a variable. Referring to Figure II-12, the wake area of wind of a point block could be significantly smaller than the wake area of a long (slab) block.
Figure II-12 Wakes of buildings
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It is therefore useful to have study areas with predominantly point blocks, and study areas with predominantly slab blocks. Streets with buildings flanking both sides could in this case be regarded as slabs.
4.3.6 Elevated Structures Extensive elevated structures will have an effect on the pedestrian wind environment underneath it. This is particularly important when the structure occupies a significant portion of the free air space above the street. An example would be the extensive footbridge network in Mong Kok.
4.4 BENCHMARKING AREA SELECTION
4.4.1 A Summary of Understanding Summarising the above scientific understanding, the following considerations could be the basis guiding the final area selection.
(A) Areas with OR without a strong prevailing wind wind-rose (B) Areas near hill or on flat land, AND exposed or not exposed (C) Areas with high, medium OR low ground coverage (D) Areas with streets parallel OR perpendicular to the prevailing wind. Consider this together with (A) above. (E) Areas with regular OR irregular street pattern. (F) Areas with different flow characteristics (different building height to street width ratios). (G) Areas with uniform building heights AND with varying building heights – (high and low building height differences). (H) Areas with point OR slab building blocks
In addition, in Hong Kong, there are streets with extensive elevated walkways, which could be noted. Density could also be noted and it could be better understood in wind engineering term as ground coverage [(C) above] and flow characteristics [(F) above]. In this study, density refers to the ―bulk‖ or volume of buildings in the area. There is no need to factor in the population density.
A key purpose of the benchmarking test is to relate the building bulks to wind availability at pedestrian level. Thus, the land use of the building is not relevant but will be noted for further references.
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4.4.2 A Taxonomic Understanding – With Examples Based on the summary, the following 19 selection parameters could be identified.
(A1) Areas with a strong prevailing wind wind-rose (A2) Areas without a strong prevailing wind wind-rose (B1) Areas near hill (B2) Areas on flat land (B3) Areas exposed (B4) Areas not exposed (C1) Areas with high ground coverage (C2) Areas with medium ground coverage (C3) Areas with low ground coverage (D1) Areas with streets parallel to the prevailing wind (D2) Areas with streets perpendicular to the prevailing wind (E1) Areas with regular street pattern (E2) Areas with irregular street pattern (F1) Areas with Isolated roughness flow characteristics (low building height to street width ratio) (F2) Areas with Wake interference flow characteristics (medium building height to street width ratio) (F3) Areas with Skimming flow characteristics (high building height to street width ratio) (G1) Areas with uniform building heights (G2) Areas with varying building heights (H1) Areas dominated by point blocks (H2) Areas dominated by slab blocks (I1) High density (I2) Medium density (I3) Low density (J1) Presence of elevated structure (K1) Pre-dominant land use (Industrial) (K2) Pre-dominant land use (Commercial) (K3) Pre-dominant land use (Residential)
The exact benchmarking areas to be studied will be worked out following the above understanding and selection parameters.
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4.4.3 Area Selections and Positioning of Test Points Taking into account the above scientific understandings, the procedures of area selection may be as follow:
1. Broadly categorise Hong Kong pedestrian wind environment into 2 categories (A1) and (A2) based on the wind data of Hong Kong Observatory, EPD‘s MM5 and HKUST‘s MM5. 2. Under (1), broadly categorise urban areas near hill (B1) or on flat land (B2), and exposed (B3) or not exposed (B4). 3. Superimpose (1) and (2) and identify key districts. 4. Broadly categorise ground coverage into high, medium and low (C1), (C2) and (C3); and select a number of representative areas under the three coverage categories. 5. Based on (4), identify areas with different street patterns (D1), (D2) and (E1), (E2). Consider this with (H1) and (H2). 6. Lastly, examine building height to street width ratios for (F1), (F2), (F3), (G1), (G2), (H1) and (H2). Typically, it is expected that within a selected area, there are sub-areas with characteristics of (F1) to (H2). The positioning of test points goes hand in hand with the area selection. For example, for areas with wide and narrow streets, test points will be inserted to capture their respective characteristics.
These systematic steps will ensure that all of the more representative pedestrian wind conditions are included. Based on the above steps, the study has selected 10 pairs of areas for testing.
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PART II(B): WIND TUNNEL BENCHMARKING STUDIES RESULTS
PART II(B)-1 INTRODUCTION
1.1 THE STUDY This section summarised the benchmarking studies using the wind tunnel tests for Batch 1 and Batch 2 study areas.
Batch 1 comprises the following 5 pairs (i.e. 10) study areas: 1. Tsim Sha Tsui (Kimberley Road – Carnarvon Road – Cameron Road Areas); 2. Tsim Sha Tsui (Granville Road – Chatham Road Souths – Mody Square Areas); 3. Mong Kok (Lai Chi Kok Road – Prince Edward Road West – Playing Field Road – Portland Street Areas); 4. Mong Kok (Nathan Road – Sai Yee Street – Bute Street – Mong Kok Road Areas); 5. Sheung Wan (Connaught Road Central – Bonham Strand – Wing Wo Street – Jubilee Street Areas); 6. Sheung Wan (Wellington Street – Staunton Street – Aberdeen Street Areas); 7. Causeway Bay (Yee Wo Street –Hysan Avenue – Lee Garden Road Areas); 8. Causeway Bay(Gloucester Road – Great George Street – Paterson Street Areas); 9. Tsuen Wan (Chung On Street – Sha Tsui Road – Yeung Uk Road Areas); 10. Tsuen Wan (Ma Tau Pa Road – Texaco Road – Wang Lung Street Areas).
Batch 2 comprises the following 5 pairs (i.e. 10) study areas: 1. San Po Kong (Tai Yau Street – Sam Chuk Street – Tsat Po Street – Pat Tat Street); 2. San Po Kong (Yi Lun Street – Shung Ling Street – Fu Yuen Street); 3. Tuen Mun (Pui To Road –Tuen Mun Heung Sze Wui Road – Ho Pang Street – Tuen Mun Road); 4. Tuen Mun (Pui To Road –Tuen Mun Heung Sze Wui Road – Tuen Hop Street – Tuen Mun Road); 5. Sha Tin (Siu Lek Yuen – Ngan Shing Street – Pak Tak Street – Tak Wing Street); 6. Sha Tin (Pak Tak Street – Tak Po Street – Tak Yi Street - Ngan Shing Street); 7. Tseung Kwan O (Po Lam Road North – Po Fung Road); 8. Tseung Kwan O (Po Fung Road – Mau Yim Road – Mau Tai Road); 9. Wong Chuk Hang (Yip Yan Street – Wong Chuk Hang Road – Heung Yip Road); 10. Wong Chuk Hang ( Welfare Road – Nam Long Shan Road)
The rationale of selecting the 20 study areas has been recorded in Part IIA.
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Wind tunnel model study was undertaken in accordance with current international best practice requirements. 1:2000 site wind availability study and 1:400 air ventilation assessment study have been conducted. This section summarises the experimental findings.
Where appropriate, the data reported here could be used later for the following studies: - comparison with the results of CFD studies; - validation for the drafting of urban climate map; - understanding of the wind performance inside the urban canopy layer level; and - cross-referencing with user survey data.
The Benchmarking Studies adopts the following technical procedures, comprising 2 parts, namely the experimental site wind availability study and the air ventilation assessment.
Wind tunnel model tests were conducted by the CLP Power Wind/Wave Tunnel Facility (WWTF) at the Hong Kong University of Science and Technology. The study was undertaken in accordance with the current international best practice in wind engineering as stipulated in the Australasian Wind Engineering Society Quality Assurance Manual, AWES- QAM-1-2001 (2001) and the American Society of Civil Engineers Manual and Report on Engineering Practice No. 67 for Wind Tunnel Studies of Buildings and Structures (1999). The study was also conducted in accordance with the recommendations of the Planning Department‘s Feasibility Study for Establishment of Air Ventilation Assessment System – Final Report (2005) and the Technical Guide for Air Ventilation Assessment in Hong Kong (2005).
1.1.1 EXPERIMENTAL SITE WIND AVAILABILITY STUDY (i) A 1:2000 scale topographical study was undertaken to determine the effects of local topography and the surrounding urban environment on mean wind direction, mean wind speed and turbulence intensity at a nominated study area in Causeway Bay.
(ii) A miniature pressure probe was used to take measurements of three components of wind speed, i.e. in the longitudinal, lateral and vertical directions, at 22.5º increments for the full 360º azimuth, i.e. for the sixteen wind directions, and at nine different heights to determine profiles of mean wind speed and turbulence intensity above the study area that will be used as input boundary conditions for later more detailed benchmarking studies. The 1:2000 scale topographical model had included the surrounding area up to a distance of approximately 10 km from the study area.
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(iii) The topographical study results were combined with WWTF‘s statistical model of the Hong Kong wind climate, based on measurements of non-typhoon winds taken by HKO at Waglan Island during the period of 1953 – 2000 inclusive, to determine wind roses corresponding to annual mean wind speeds at the study area.
1.1.2 AIR VENTILATION ASSESSMENT (i) A 1:400 scale model of the study area and surrounding areas was fabricated to represent the state of the urban areas corresponding to the existing condition in November 2006. The model included all known existing surrounding buildings, structures and topographical features within a diameter of approximately 1160 m, in accordance with plans, drawings and information supplied by The Chinese University of Hong Kong on 5 March 2007. Trees within the modelled regions were modelled with foliage and in their mature growth state.
(ii) A 1:2000 scale site wind availability study has been undertaken previously (WWTF Investigation Report WWTF008-2007) to determine the effects of local topography on mean wind direction, mean wind speed and turbulence intensity of non-typhoon winds approaching the nominated study area. The results of that study were combined with a probabilistic model of the Hong Kong non-typhoon wind climate, based on wind speed and direction measurements taken by HKO at Waglan Island during the period of 1953 – 2000 inclusive, to determine the site wind availability for the nominated study area.
(iii) Wind speeds were measured at test points within the nominated study area for 16 the wind directions ranging from 22.5º to 360º (north) at increments of 22.5º using a multi- channel thermal anemometer system. Directional wind velocity ratios were measured at each individual test point and subsequently combined with the site wind availability data to determine the overall wind velocity ratios, site wind velocity ratios and local wind velocity ratios for three zones within the nominated study area, both on an annual basis and, during the summer months only. Mean wind speeds corresponding to a probability of occurrence of 50% on an annual basis and a probability of occurrence of 50% during summer months only were also determined at each measurement location.
1.2 DATA SUMMARY
The wind tunnel tests data are summarised below.
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Batch 1 The following tables (Table II-1 to 4) give a summary of the findings for all the test sites in the form of VRw and wind speed for both annual and summer cases. After reviewing the wind tunnel test results, a generic understanding of connection between the urban morphology and the VR is summarised in Table II-5. Detailed findings of the above studies for each site will be reported separately in the corresponding section.
Table II-1a Annual VRw of the test sites
Table II-1b Statistical summary of the annual VRw of the test sites
Test Site VRw_min VRw_max VRw_mean VRw_median Causeway Bay A 0.15 0.28 0.21 0.22 Causeway Bay B 0.08 0.25 0.16 0.16 Sheung Wan A 0.06 0.32 0.18 0.18 Sheung Wan B 0.04 0.20 0.09 0.09 Mong Kok A 0.09 0.24 0.16 0.15 Mong Kok B 0.05 0.33 0.16 0.14 Tsim Sha Tsui A 0.04 0.18 0.12 0.13 Tsim Sha Tsui B 0.07 0.27 0.14 0.14 Tsuen Wan A 0.10 0.25 0.15 0.16 Tsuen Wan B 0.14 0.36 0.25 0.27
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Table II-2a Summer VRw of the test sites
Table II-2b Statistical summary of the summer VRw of the test sites
Test Site VRw_min VRw_max VRw_mean VRw_median Causeway Bay A 0.09 0.27 0.15 0.14 Causeway Bay B 0.08 0.26 0.15 0.15 Sheung Wan A 0.05 0.31 0.15 0.15 Sheung Wan B 0.05 0.19 0.09 0.09 Mong Kok A 0.09 0.23 0.15 0.14 Mong Kok B 0.04 0.36 0.16 0.13 Tsim Sha Tsui A 0.04 0.19 0.11 0.12 Tsim Sha Tsui B 0.06 0.23 0.13 0.12 Tsuen Wan A 0.12 0.27 0.18 0.18 Tsuen Wan B 0.15 0.34 0.25 0.26
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Table II-3a median wind speed distribution of the test sites for annual case
Table II-3b Statistical summary of the median annual wind speed (m/s) of the test sites
Test Site WS_min WS_max WSw_mean WSw_median Causeway Bay A 0.59 1.92 1.30 1.31 Causeway Bay B 0.51 1.63 1.02 1.03 Sheung Wan A 0.32 1.94 1.08 0.94 Sheung Wan B 0.26 1.28 0.57 0.53 Mong Kok A 0.60 1.64 1.07 1.05 Mong Kok B 0.37 2.32 1.13 0.94 Tsim Sha Tsui A 0.25 1.24 0.81 0.86 Tsim Sha Tsui B 0.45 1.54 0.96 0.99 Tsuen Wan A 0.60 1.63 0.95 0.96 Tsuen Wan B 0.81 2.35 1.63 1.72
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Table II-4a median wind speed distribution of the test sites for summer case
Table II-4b Statistical summary of the median summer wind speed (m/s) of the test sites
Test Site WS_min WS_max WS_mean WS_median Causeway Bay A 0.16 0.76 0.36 0.35 Causeway Bay B 0.19 0.72 0.40 0.39 Sheung Wan A 0.20 1.21 0.54 0.49 Sheung Wan B 0.17 0.76 0.35 0.33 Mong Kok A 0.44 1.20 0.72 0.68 Mong Kok B 0.19 1.95 0.80 0.66 Tsim Sha Tsui A 0.17 0.90 0.52 0.54 Tsim Sha Tsui B 0.22 0.83 0.52 0.49 Tsuen Wan A 0.49 1.19 0.73 0.72 Tsuen Wan B 0.63 1.50 1.06 1.04
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Table II-5 A generic understanding of connection between the urban morphology and the VR
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Batch 2 The following tables (Tables II-6 to 9) give a summary of the findings for all the study areas in Batch 2 in the form of VRw and wind speed for both annual and summer cases. After reviewing the wind tunnel test results, a generic understanding of connection between the urban morphology and the VR is summarised in Table II-10. Detailed findings of the above studies for each study area will be reported separately in the corresponding section.
Table II-6a Annual VRw of the study areas
0.25
0.20
0.15 Probability 0.10 Wong Wong Chuk 0.05 Tseung Chuk Hang A Tseung Kw an O B Hang A 0.00 Sha Tin B Kw an O Sha Tin A A
Tuen Mun
0.01 0.05
0.09 Tuen Mun B 0.13
0.17 A
0.21 San Po 0.25
VRw-annual 0.29 Kong B
0.33 San Po 0.37
0.41 Kong A
Table II-6b Statistical summary of the annual VRw of the study areas Study Areas VRw_min VRw_max VRw_mean VRw_median San Po Kong A 0.08 0.2 0.14 0.14 San Po Kong B 0.07 0.18 0.12 0.12 Tuen Mun A 0.11 0.25 0.16 0.15 Tuen Mun B 0.11 0.26 0.19 0.19 Sha Tin A 0.12 0.29 0.21 0.2 Sha Tin B 0.14 0.24 0.2 0.2 Tseung Kwan O A 0.11 0.26 0.17 0.17 Tseung Kwan O B 0.09 0.25 0.19 0.19 Wong Chuk Hang A 0.1 0.26 0.19 0.18 Wong Chuk Hang B 0.13 0.33 0.22 0.23
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Table II-7a Summer VRw of the study areas
0.30 0.25 A 0.20
Probability 0.15
Wong Chuk 0.10 Hang B Wong Chuk Hang A Tseung 0.05 Kwan O B Tseung Kwan O A Sha Tin B
0.00 Sha Tin A
Tuen Mun B
0.01
0.04 0.1
0.07 Tuen Mun A
0.13
0.16 0.19
0.22 San Po
0.25 0.28
VRw-summer 0.31 Kong B
0.34 San Po
0.4 0.37
0.43 Kong A
Table II-7b Statistical summary of the summer VRw of the study areas Study Areas VRw_min VRw_max VRw_mean VRw_median San Po Kong A 0.08 0.2 0.15 0.16 San Po Kong B 0.09 0.22 0.15 0.15 Tuen Mun A 0.12 0.3 0.17 0.16 Tuen Mun B 0.09 0.3 0.19 0.19 Sha Tin A 0.12 0.26 0.17 0.17 Sha Tin B 0.14 0.24 0.2 0.2 Tseung Kwan O A 0.12 0.21 0.16 0.16 Tseung Kwan O B 0.1 0.22 0.18 0.18 Wong Chuk Hang A 0.1 0.3 0.2 0.19 Wong Chuk Hang B 0.14 0.33 0.23 0.24
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Table II-8a meam wind speed distribution of the study areas for annual case
0.30 0.25 0.20 A Probability 0.15
0.10 Wong Wong Chuk Hang B Tseung Chuk Hang 0.05 A Tseung Kw an O B Sha Tin B Kw an O A 0.00 Sha Tin A
Tuen Mun 0.05
0.25 B
0.45 Tuen Mun 0.65
0.85 A
1.05 San Po 1.25
1.45 Kong B
Wind velocity (m/s) 1.65 San Po 1.85 2.05 Kong A
Table II-8b Statistical summary of the median annual wind speed (m/s) of the study areas
Study Areas WS_min WS _max WS _mean WS _median
San Po Kong A 0.78 2.27 1.53 1.52 San Po Kong B 0.83 1.95 1.33 1.32 Tuen Mun A 0.67 1.35 0.92 0.88 Tuen Mun B 0.67 1.67 1.15 1.12 Sha Tin A 1.05 2.41 1.72 1.69 Sha Tin B 1.07 2.13 1.64 1.66 Tseung Kwan O A 0.62 1.64 1 0.98 Tseung Kwan O B 0.55 1.47 1.15 1.17 Wong Chuk Hang A 0.65 1.69 1.22 1.24 Wong Chuk Hang B 0.88 2.16 1.47 1.5
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Table II-9a median wind speed distribution of the study areas for summer case
0.25
0.20 A 0.15 Probability 0.10 Wong Chuk Wong Chuk Hang B 0.05 Tseung Hang A Tseung Kw an O B Sha Tin B Kw an O A 0.00 Sha Tin A
Tuen Mun 0.05
0.25 B
0.45 Tuen Mun 0.65
0.85 A
1.05 San Po 1.25
1.45 Kong B
Wind velocity (m/s) 1.65 San Po 1.85
2.05 Kong A
Table II-9b Statistical summary of the median summer wind speed (m/s) of the study areas Study Areas WS_min WS _max WS _mean WS _median San Po Kong A 0.64 1.74 1.24 1.29 San Po Kong B 0.75 1.92 1.27 1.27 Tuen Mun A 0.6 1.43 0.84 0.79 Tuen Mun B 0.47 1.53 0.96 0.94 Sha Tin A 0.91 1.94 1.23 1.21 Sha Tin B 1.04 1.91 1.54 1.54 Tseung Kwan O A 0.61 1.15 0.85 0.88 Tseung Kwan O B 0.52 1.22 0.95 0.98 Wong Chuk Hang A 0.52 1.76 1.06 1.08 Wong Chuk Hang B 0.71 1.91 1.32 1.31
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Table II-10 A generic understanding of connection between the urban morphology and the VR
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1.3 REMARKS Two general remarks concerning physical model and test probes used in 1:400 testing are as follows:
(a) The wind tunnel models were designed to represent the general building massing and configurations to meet the objectives of the benchmarking studies. Hence, openings in both buildings and podia were not included in the wind tunnel models. (b) Each measurement probe of the thermal anemometer system was calibrated prior to conducting each of the benchmarking studies. The calibrations were performed over a range of wind speeds, extending to less than 1 m/s, and the regression coefficients for the calibrations for each measurement probe were greater than 0.999. Therefore, the thermal anemometer system used for the benchmarking studies was capable of measuring wind speeds less than 1 m/s.
PART II(B)-2 THE SUMMARY OF THE WIND TUNNEL TESTS FOR BATCH I STUDY AREAS
Detailed findings for each study area are reported below.
2.1 CAUSEWAY BAY The annual and summer (i.e. June, July, August) prevailing wind characteristics corresponding to strong non-typhoon winds approaching Hong Kong also occurred at a height of 500 m above the Causeway Bay study area. However, at a height of 50 m above the study area, winds from directions of 45º to 90º, 157.5º to 180º and 247.5 were significantly affected by the surrounding topography that caused significant changes to the wind rose at that height. Similarly, at heights of 100 m and 200 m, winds from directions of 67.5 and 180 were also significantly affected by the surrounding topography. Winds approaching the study area from northerly directions were the least affected due to the relatively open exposure to Victoria Harbour in those directions.
There are in total 91 test points. In general, higher wind velocity ratios were determined at test points located near the Victoria Park and Victoria Harbour. Test points that were located in narrow streets such as Lee Garden Road and Pak Sha Road, away from areas with relatively open exposure, recorded significantly lower wind velocity ratios. It was also clearly demonstrated that the weak summer sea breezes that dominate the summer wind climate do not significantly penetrate the urban environment in the Causeway Bay study area.
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Figure II-13: Locations of test points at Causeway Bay
The annual site wind velocity ratios for Zones A, B and C in the Causeway Bay study area are 0.21, 0.17 and 0.22 respectively. The annual local wind velocity ratios for Zones A, B and C in the Causeway Bay study area are 0.21, 0.16 and 0.20 respectively. The annual mean wind speeds corresponding to a probability of occurrence of 50% for Zone A, B and C are 1.30, 1.02 and 1.23 m/s respectively.
The summer site wind velocity ratios for Zones A, B and C in the Causeway Bay study area are, 0.16, 0.16 and 0.19 respectively. The summer local wind velocity ratios for Zones A, B and C in the Causeway Bay study area are 0.15, 0.15 and 0.16 respectively. The mean wind speeds corresponding to a probability of occurrence of 50% in summer for Zone A, B and C are 0.36, 0.40 and 0.41 m/s respectively.
2.2 SHEUNG WAN In general, the annual and summer (i.e. June, July, August) prevailing wind characteristics corresponding to strong non-typhoon winds approaching Hong Kong also occurred at a
School of Architecture, CUHK Page 313 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT height of 500 m above the Sheung Wan study area. However, at heights of 200 m and below, wind conditions for a number of wind directions were significantly affected by a combination of the mountains on Hong Kong Island and the density of the built environment in the nearby urban areas. Winds approaching from wind directions of 45°, 315° and 337.5° were the least affected at all heights.
There are in total 95 test points. In general, the density of buildings and the narrower streets in the southern part of the study area (Zone B), i.e. south of Queen‘s Road Central around Aberdeen Street, Peel Street, Graham Street and Cochrane Street, are likely to be the primary reason for the inability of the prevailing winds to penetrate the southern parts of the Sheung Wan study area. In contrast, the mixed building heights and relatively wide roads in closer proximity to the ocean frontage in the northern part of the study area (Zone A) were generally less obstructive to prevailing wind flows.
Figure II-14: Locations of test points at Sheung Wan
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The annual site wind velocity ratios for Zones A, B and C in the Sheung Wan study area are 0.18, 0.09 and 0.18 respectively. The summer site wind velocity ratios for Zones A, B and C in Sheung Wan study area are 0.15, 0.10 and 0.15 respectively.
The annual local wind velocity ratios for Zones A, B and C in the Sheung Wan study area are 0.18, 0.09 and 0.14 respectively. The summer local wind velocity ratios for Zones A, B and C in the Sheung Wan study area are 0.15, 0.09 and 0.12 respectively.
The average annual mean wind speeds corresponding to a probability of occurrence of 50% for Zone A, B and C are 1.05, 0.57 and 0.85 m/s respectively. The average summer mean wind speeds corresponding to a probability of occurrence of 50% for Zone A, B and C are 0.52, 0.35 and 0.45 m/s respectively.
2.3 MONG KOK The annual and summer (i.e. June, July, August) prevailing wind characteristics corresponding to strong non-typhoon winds approaching Hong Kong also occurred at a height of 500 m above the Mong Kok study area. However, at heights of 50 m, 100 m and 200 m above the study area, winds from directions of 22.5º, 67.5º, 315º and 337.5 were significantly affected by the surrounding topography that caused significant changes to the wind roses at those heights. Significant reductions in the measured magnitudes of wind speed are considered to be caused by the density and heights of the nearby built-up areas in the south and west of Kowloon. Winds approaching from easterly directions were the least affected due to the area‘s relatively open exposure for those directions.
There are in total 92 test points. In general, higher wind velocity ratios were determined at test points located along Nathan Road north of Mong Kok Road, in the wider, more open eastern part of Mong Kok Road, and south of Mong Kok Road between Nathan Road and Fa Yuen Street. Test points that were located in secondary narrow streets, away from the main wider roads such as Nathan Road, recorded significantly lower wind velocity ratios.
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Figure II-15: Locations of test points at Mong Kok
The annual site wind velocity ratios for Zones A, B and C in the Mong Kok study area are 0.15, 0.18 and 0.21 respectively. The annual local wind velocity ratios for Zones A, B and C in the Mong Kok study area are 0.16, 0.16 and 0.16 respectively. The annual mean wind speeds corresponding to a probability of occurrence of 50% for Zone A, B and C are 1.07, 1.13 and 1.13 m/s respectively.
The summer site wind velocity ratios for Zones A, B and C in the Mong Kok study area are 0.15, 0.18 and 0.19 respectively. The summer local wind velocity ratios for Zones A, B and C in the Mong Kok study area are 0.15, 0.16 and 0.15 respectively. The mean wind speeds corresponding to a probability of occurrence of 50% in summer for Zone A, B and C are 0.72, 0.80 and 0.77 m/s respectively.
2.4 TSIM SHA TSUI The annual and summer (i.e. June, July, August) prevailing wind characteristics corresponding to strong non-typhoon winds approaching Hong Kong also occurred at a height of 500 m above the Tsim Sha Tsui study area. However, at a height of 50 m and 100 m
School of Architecture, CUHK Page 316 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT above the study area, winds from directions of 112.5º, 202.5, 247.5, 270 and 360º were significantly affected by the surrounding topography including the mountains in the northern parts of Kowloon, to the south of the study area on Hong Kong Island and the density and heights of the nearby built-up areas in Kowloon. The same wind directions saw corresponding significant reductions in the magnitudes of mean wind speed. At a height of 200 m, winds from directions 202.5 and 270 were also significantly affected by the surrounding topography. In general, winds approaching from easterly directions were the least affected due to the area‘s relatively open exposure in those directions.
There are in total 94 test points. Low magnitudes of overall wind velocity ratio were recorded in narrower streets in Zone A (east of Chatham Road South) such as Knutsford Terrace, Hau Fook Street and Granville Circuit. Zone B (west of Chatham Road South) is more exposed to winds from the north and southeasterly directions and the annual average mean wind speed corresponding to a probability of occurrence of 50% was approximately 19% greater for Zone B than for Zone A. However, local wind conditions at specific test points are also significantly affected by the immediate surroundings, such as nearby buildings, which tend to balance out over the study area resulting in similar site wind velocity ratios and local wind velocity ratios for both Zone A and Zone B.
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Figure II-16: Locations of test points at Tsim Sha Tsui
The annual site wind velocity ratios for Zones A, B and C in the Tsim Sha Tsui study area are 0.12, 0.15 and 0.16 respectively. The annual local wind velocity ratios for Zones A, B and C in the Tsim Sha Tsui study area are 0.12, 0.14 and 0.14 respectively. The annual average mean wind speeds for Zone A, B and C are 0.81, 0.96 and 0.96 m/s respectively.
The summer site wind velocity ratios for Zones A, B and C in the Tsim Sha Tsui study area are 0.11, 0.13 and 0.15 respectively. The summer local wind velocity ratios for Zones A, B and C in the Tsim Sha Tsui study area are 0.11, 0.13 and 0.13 respectively. The mean wind speeds corresponding to a probability of occurrence of 50% in summer for Zone A, B and C are 0.52, 0.52 and 0.57 m/s respectively.
2.5 TSUEN WAN The annual and summer (i.e. June, July, August) prevailing wind characteristics corresponding to strong non-typhoon winds approaching Hong Kong also occurred at a height of 500 m above the Tsuen Wan study area. However, at heights of 50 m and 100 m above the study area, winds from directions of 90º, 112.5º, 135º, 292.5, 315 and 337.5
School of Architecture, CUHK Page 318 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT were significantly affected by the topography surrounding the study area which caused significant changes to the wind rose at those heights. Similarly, at a height of 200 m, winds from directions of 112.5 and 315 were also significantly affected by the surrounding topography. Winds approaching from westerly directions were the least affected due to the area‘s relatively open exposure in those directions.
There are in total 85 test points. In general, stronger wind conditions were recorded in the southern half of the Tsuen Wan study area, on both an annual basis and for summer months, with higher recorded values of overall wind velocity ratios and average mean wind speeds corresponding to a probability of occurrence of 50%. This is attributed to the more open exposure of the southern half of the study area to the prevailing winds from east-north-east (annual and summer) and the south-west quadrant (summer), the greater mixture of building heights and a potentially more favourable alignment and arrangement of streets in that area. Significantly lower wind velocity ratios were recorded in Zone A north of the junction of Yeung Uk Road and Luen Yan Street.
Figure II-17: Locations of test points at Tsuen Wan
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The annual site wind velocity ratios for Zones A, B and C in the Tsuen Wan study area are 0.16, 0.25 and 0.21 respectively. The annual local wind velocity ratios for Zones A, B and C in the Tsuen Wan study area are 0.15, 0.26 and 0.21 respectively. The average annual mean wind speeds corresponding to a probability of occurrence of 50% for Zone A, B and C are 0.95, 1.67 and 1.32 m/s respectively.
The summer site wind velocity ratios for Zones A, B and C in the Tsuen Wan study area are 0.19, 0.26 and 0.24 respectively. The summer local wind velocity ratios for Zones A, B and C in the Tsuen Wan study area are 0.18, 0.25 and 0.23 respectively. The average summer mean wind speeds corresponding to a probability of occurrence of 50% for Zone A, B and C are 0.72, 1.07 and 0.94 m/s respectively.
2.6 SAN PO KONG In general, the annual prevailing wind characteristics corresponding to non-typhoon winds at an elevation of 500 mPD above the San Po Kong Study Area were similar to the overall characteristics of non-typhoon winds approaching the Hong Kong region, although the magnitudes of the directional wind speeds were reduced. More significant changes were observed in the summer prevailing wind characteristics, which is mainly due to the effects of hilly terrain on Hong Kong Island to the south-west of the Study Area.
Significant reductions in the measured magnitudes of wind speed were mainly caused by the mountains located to the north-west of the Study Area, such as Lion Rock, north-east of the Study Area, such as Tate‘s Cairn, and east of the Study Area on Kowloon, and on Hong Kong Island. Those mountains significantly affected the directional characteristics for wind directions of 67.5º, 90º, 225º and 315. Winds approaching the Study Area from 157.5 were the least affected due to the relatively open sea exposure at the Lei Yue Mun entrance to Victoria Harbour.
There are in total 94 test points. In general, the magnitudes of the annual overall wind velocity ratios and annual average mean wind speeds were greater in the northern half of the San Po Kong Study Area. This is attributed to the more open exposure of the northern half of the Study Area to the annual prevailing winds from the north-east quadrant, the relatively wider spaces between the buildings and the potentially more favourable alignment and arrangement of streets in that area. On a summer basis, the overall wind velocity ratios and average mean wind speeds corresponding to a probability of exceedance of 50% were approximately the same for Zone A and Zone B.
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Figure II-18: Locations of test points at San Po Kong
The annual site wind velocity ratios for Zones A, B and C in the San Po Kong Study Area are 0.13, 0.12 and 0.17 respectively. The annual local wind velocity ratios for Zones A, B and C in the San Po Kong Study Area are 0.14, 0.12 and 0.15 respectively. The average annual mean wind speeds corresponding to a probability of exceedance of 50% for Zone A, B and C are 1.53, 1.33 and 1.72 m/s respectively.
The summer site wind velocity ratios for Zones A, B and C in the San Po Kong Study Area are 0.14, 0.15 and 0.18 respectively. The summer local wind velocity ratios for Zones A, B and C in the San Po Kong Study Area are 0.15, 0.15 and 0.17 respectively. The average summer mean wind speeds corresponding to a probability of exceedance of 50% for Zone A, B and C are 1.24, 1.27 and 1.46 m/s respectively.
2.7 TUEN MUN In general, the annual and summer prevailing wind characteristics corresponding to non- typhoon winds at a elevation of 500 m above the Tuen Mun Study Area were similar to the overall characteristics of non-typhoon winds approaching the Hong Kong region, although the magnitudes of the directional wind speeds were reduced.
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Significant reductions in the measured magnitudes of wind speed were caused by Kau Keng Shan to the east of the Study Area, Castle Peak to the west of the Study Area and built-up areas to the south of the Study Area. The valley and the river channel features at the Tuen Mun Study Area had significant affects on the wind directions measured at the site at elevations below 150 m for approaching wind directions of 45°, 67.5°, 135°, 225°, 247.5°, 270°, 292.5°, 315° and 337.5°. Winds approaching from the north and north-north-east were the least affected due to the area‘s relatively open exposure in those directions.
There are in total 95 test points. In general, the magnitudes of the overall wind velocity ratios were greater in the South Focus Area than the North Focus Area. This is attributed to difference in street width, street alignment, the substantial separations between the buildings and the effects of the taller buildings and more extensive podia in the South Focus Area.
Relatively high overall wind velocity ratios were measured at the immediate surroundings of the committed development at Pui To Road within the Study Area and along Tuen Shun Street. These conditions are attributed to the effects of the nearby taller buildings and podia. Relatively low wind velocity ratios were measured at sheltered locations including areas underneath the elevated road at Pui To Road, below the Tuen Mun West Rail Station, as well as in the vicinity of Yan Oi Town Square which is affected by the nearby low-rise, elongated buildings.
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Figure II-19: Locations of test points at Tuen Mun
The measured annual and summer overall wind velocity ratios were within the range of 0.09 - 0.30. The annual and summer LVR for the Study Area are 0.18 and 0.19 respectively. The annual and summer LVR for the North Focus Area are 0.16 and 0.17 and the annual and summer LVR for the South Focus Area are 0.19 and 0.19.
The annual and summer average mean wind speeds of all test locations corresponding to a probability of exceedance of 50% for the Tuen Mun Study Area are 1.07 and 0.94 m/s respectively. The annual average mean wind speeds for the North and South Focus Areas are 0.92 and 1.15 m/s respectively. The summer average mean wind speeds for the North and South Focus Areas are 0.84 and 0.96 m/s respectively.
2.8 SHA TIN In general, the annual prevailing wind characteristics corresponding to non-typhoon winds at an elevation of 500 mPD above the Sha Tin Study Area were similar to the overall characteristics of non-typhoon winds approaching the Hong Kong region, although the magnitudes of the directional wind speeds were reduced. More significant changes were observed at lower elevations due to the combination of buildings and mountains surrounding the Study Area.
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The largest reductions in the measured magnitudes of wind speed were mainly caused by the mountains to the south and south-west of the Study Area. The presence of mountains significantly affected the directional characteristics for all wind directions with the highest reductions for the wind directions of 180 202.5, 225 and 247.5. Winds approaching the Study Area from 67.5º were the least affected due to the open sea exposure at Sha Tin Hoi.
There are in total 94 test points. On an annual basis, marginally higher wind conditions were recorded in the northern part of the Sha Tin Study Area. This was attributed to the more open exposure of the northern half of the Study Area to the annual prevailing winds from the north-east quadrant, the proximity of the area to Shing Mun River Channel and a potentially more favourable alignment and arrangement of streets in that area. However, these benefits are apparently offset to a certain extent by the moderating effects of Ngan Shing Commercial Centre and City One Plaza on pedestrian level wind speeds.
On a summer basis, pedestrian level wind conditions are likely to be better in Zone B than Zone A. This is mainly attributed to the penetration of south-west winds into Zone B that are also enhanced as they flow between and around the tall buildings in Zone B. In Zone A, south-west winds are moderated by Ngan Shing Commercial Centre.
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Figure II-20: Locations of test points at Sha Tin
The annual local wind velocity ratios for Zones A, B and C in the Sha Tin Study Area are 0.21, 0.20 and 0.22 respectively. The average annual mean wind speeds corresponding to a probability of exceedance of 50% for Zone A, B and C are 1.72, 1.64 and 1.87 m/s respectively. The average annual spatial wind velocity ratios for the elevated test points, all of which are located in Zones B and C, are 0.18 and 0.22 respectively.
The summer local wind velocity ratios for Zones A, B and C in the Sha Tin Study Area are 0.17, 0.20 and 0.18 respectively. The average summer mean wind speeds corresponding to a probability of exceedance of 50% for Zone A, B and C are 1.23, 1.54 and 1.26 m/s respectively. The average summer spatial wind velocity ratios for the elevated test points in Zones B and C are 0.20 and 0.19 respectively.
2.9 TSUENG KWAN O In general, the annual prevailing and summer wind characteristics corresponding to non- typhoon winds at an elevation of 500 mPD above the Tseung Kwan O Study Area were similar to the overall characteristics of non-typhoon winds approaching the Hong Kong region, although the magnitudes of the directional wind speeds were slightly affected by topographical effects.
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Significant reductions in the measured magnitudes of wind speed below an elevation of 200 mPD were mainly caused by the mountains to the southwest to northwest of the Study Area. Those mountains significantly affected the directional characteristics for wind directions of 202.5º, 225º, 247.5, 270º, 315 and 337.5. Winds approaching the Study Area from 90 were the least affected due to the relatively open sea exposure at Silverstrand.
There are in total 98 test points. In general, the magnitudes of the annual overall wind velocity ratios and average mean wind speeds were smaller in the northern half of the Tseung Kwan O Study Area. This is attributed to the narrower spaces between the buildings and the long plan dimensions of the buildings. The relatively wide Po Hong Road and Po Fung Road, and the park located between Tseung Kwan O Swimming Pool and King Lam Estate linking with Mau Yip Road, allow the prevailing winds to penetrate into the southern areas of the Study Area. The subsequent interaction with the buildings in those areas result in enhanced pedestrian level wind speeds for a number of wind directions.
Figure II-21: Locations of test points at Tseung Kwan O
The annual local wind velocity ratios for Zones A, B, C and D in the Tseung Kwan O Study Area are 0.17, 0.19, 0.19 and 0.23 respectively. The average annual mean wind speeds
School of Architecture, CUHK Page 326 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT corresponding to a probability of exceedance of 50% for Zone A, B, C and D are 1.00, 1.15, 1.14 and 1.32 m/s respectively.
The summer local wind velocity ratios for Zones A, B, C and D in the Tseung Kwan O Study Area are 0.16, 0.18, 0.20 and 0.20 respectively. The average summer mean wind speeds corresponding to a probability of exceedance of 50% for Zone A, B, C and D are 0.85, 0.95, 1.10 and 1.07 m/s respectively.
2.10 WONG CHUK HANG In general, the annual and summer prevailing wind characteristics corresponding to non- typhoon winds at an elevation of 500 mPD above the Wong Chuk Hang Study Area were similar to the overall characteristics of non-typhoon winds approaching the Hong Kong region, although the magnitudes of the directional wind speeds were reduced.
Significant reductions in the measured magnitudes of wind speed were mainly caused by the mountains surrounding the Study Area and nearby built-up areas. The valley and the channel features significantly affected the directional characteristics for wind directions of 45º, 135º, 157.5, 180º, 225º, 247.5 and 337.5. Upper level winds approaching from the 157.5, 180, 247.5 and 270 i.e. directions approximately aligned with Po Chong Wan and Shek Pai Wan, were the least affected due to the exposures to wind flow above the water channels.
There are in total 87 test points. In general, the magnitudes of the overall wind velocity ratios were greater in Zone B than in Zone A. For annual winds, this is attributed to the generally larger magnitudes of directional wind velocity ratios in Zone B for easterly winds. For the summer months, winds from the south-west quadrant are able to better penetrate into Zone B due to its closer proximity to the open water of Sham Wan. The orientation and close spacing of buildings in Zone A generally obstruct the penetration of south to south-westerly winds. The valley location of the Wong Chuk Hang Study Area also caused some enhancement of pedestrian level wind speeds, particularly for winds from 22.5° to 112.5° inclusive. These effects were enhanced locally by the arrangement of some buildings in the Study Area, particularly those located on the east to west aligned streets in the Study Area.
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Figure II-22: Locations of test points at Wong Chuk Hang
The annual site wind velocity ratios for Zones A, B and C in the Wong Chuk Hang Study Area are 0.19, 0.24 and 0.21 respectively. The summer site wind velocity ratios for Zones A, B and C in the Wong Chuk Hang Study Area are 0.21, 0.25 and 0.22 respectively. The annual local wind velocity ratios for Zones A, B and C in the Wong Chuk Hang Study Area are 0.19, 0.22 and 0.21 respectively. The summer local wind velocity ratios for Zones A, B and C in the Wong Chuk Hang Study Area are 0.20, 0.23 and 0.22 respectively.
The annual and summer average mean wind speeds of all test locations corresponding to a probability of exceedance of 50% for the Wong Chuk Hang Study Area are 1.37 m/s and 1.25 m/s respectively. The annual average mean wind speeds for Zone A, B and C are 1.22 m/s, 1.47 m/s and 1.40 m/s respectively and the summer mean wind speeds for Zone A, B and C are 1.06 m/s, 1.32 m/s and 1.32 m/s respectively.
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PART III: ESTABLISHMENT OF WIND PERFORMANCE CRITERION
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PART IIIA: VENTILATION FOR URBAN THERMAL COMFORT
PART III(A)-1 BACKGROUND AND LITERATURE BASIS
1.1.1 Background
In 2003, the Team Clean‘s Report on Measures to Improve Environmental Hygiene in Hong Kong first mentioned the term Air Ventilation Assessment (AVA). In 2003, Planning Department commissioned a study titled ―Feasibility Study for Establishment of Air Ventilation Assessment System (AVAS)‖ which included an understanding of urban thermal comfort (Table III-1). The earlier findings were based on literature and theoretical understanding. The understanding is further elaborated in this study based on user survey data and the use of an outdoor human heat balance model.
Table III-1 An Understanding of Urban Thermal Comfort from AVAs Outdoor thermal comfort could be achieved when the following factors are balanced: air temperature, wind speed, humidity, activity, clothing and solar radiation (Figure III- 1 and 2). For designers, it is possible to design our outdoor environment to maximize wind speed and minimize solar radiation to achieve comfort in the hot tropical summer months of Hong Kong. Typically, the desirable environment over the pedestrians is a balance between air temperature, solar radiation and wind speed. A higher wind speed might be needed if a pedestrian is only partly shaded, likewise, a lower wind speed might be desired if the air temperature is lower. Based on preliminary researches, refer to the graph below, for example, when a pedestrian is under shade, a steady mean wind at pedestrian level of around 1.5 m/s will be beneficial for providing thermal relief and a comfortable outdoor urban environment in summer in Hong Kong. Factoring in the macro wind availability of Hong Kong, it might be quoted statistically that a good Outdoor probability (50% median) of achieving this 1.5 m/s mean wind speed is desirable. The Comfort criterion states here is not a standard but it is preliminary for head starting an understanding of AVA. Further local studies are desirable.
Referring to Hong Kong‘s general macro wind availability data (from the Hong Kong Observatory), in order to capture this ―mean 1.5 m/s wind over 50% of the time‖ of a year, it is desirable to have a city morphology that is optimised, and as much as possible, designed to capture the incoming macro wind availability. Properly laid out urban patterns and street widths, careful disposition of building bulks and heights, open spaces and their configurations, breezeways and air paths, and so on are all important design parameters. Achieving a quality outdoor thermal environment for Hong Kong is an important planning consideration. A well designed urban wind environment will also benefit the individual buildings and their probability of achieving indoor comfort, as well as contributing to other benefits, like the dispersion of anthropogenic wastes.
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Figure III-1 An understanding of urban thermal comfort based on CUHK researches [Cheng, V. and Ng, E., Thermal Comfort in Urban Open Spaces for Hong Kong, Architectural Science Review, vol.49, no.3, Australia, 2006, pp.236-242.]
In 2006, the AVA Technical Circular33 (TC) was promulgated by the HLPB and ETWB. There was no definitive wind performance standard then, and the TC recommends a ―options comparison and improvement‖ approach.
PART III of this study investigates the feasibility of establishing a practical wind performance criterion to create a desirable urban environment for human thermal comfort.
33 The ex-Housing, Planning and Lands Bureau (HPLB) and ex-Environment, Transport and Works Bureau jointly issued the Technical Circular No. 1/06 on ‗Air Ventilation Assessment‘ in July 2006.
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1.1.2 Literature understanding based on experimental studies
Figure III-2 Cooling effect of air movement (Khedari et al, 2000)
Figure III-3 Air Speed offered by the ∆T (Khedari et al, 2000).
In hot and humid climatic conditions, air movement assists body heat losses by evaporation of latent heat (Macfarlend, 1958) (Murakami et al, 1997) (Stathopoulos, 2004) (Aynsley and Spruill, 1990) (Nikolopoulou et al, 1998) (Nikolopoulou et al, 1999) (Nikolopoulou et al, 2001) (Nikolopoulou and Steemers, 2000) (Ahmed, 2003).
Researchers have pointed to the need for air movement for urban human thermal comfort in hot and humid climatic conditions (Figure III-2 & 3) (Khedari et al, 2000). Khedari et al have found that in high humidity environment typical of sub-tropical summer conditions in Hong Kong, the ∆T offset is in the order of 1 ○C per 0.5 m/s of air movement – data valid experimentally between 0.5 to 1.5 m/s. The researchers also note that the beneficial effects of
School of Architecture, CUHK Page 332 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT air movement are higher at air movement of 0.5 to 1.0 m/s. Data from Khedari et al have also been fitted into equations by Richard Aynsley as follow:
Based on Tanabe‘s research, Givoni (1998) has also concluded the need of wind of 1 m/s at 27 ○C and 1.6 m/s at 31 ○C.
In Hong Kong, urban thermal comfort studies conducted by researchers at CUHK have indicated that air movement has a beneficial effect of ∆T offsets in the order of 1 ○C per approximately 0.4 m/s of air movement - data valid between 0.3 to 1.0 m/s (Figure III- 4) (Cheng and Ng, 2008).
Figure III-4 A longitudinal study on urban thermal comfort by researchers of CUHK. The average slope of the thermal responses with changes in the air temperature was 0.23 units/ ⁰C. The difference between the average thermal responses in the „wind break‟ and „no wind break‟ settings was 0.43 units. Therefore, it can be inferred that the effect of increasing wind speed from 0.3 m/s to 1 m/s was equivalent to about 1.9 ⁰C drop in air temperature.
1.1.3 Literature understanding based on heat balance modelling Apart from researches that directly deal with air movement for thermal comfort, researchers have also relied on human heat energy balance modelling (Figure III- 5) to gain an understanding of the human comfort needs for air movement. Bio-climatically, the human body exchanges heat with its environment. The balance of the heat exchange depends on a number of personal and environmental factors (Table III- 2).
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Figure III-5 The parameters of the human heat balance (Houghton, 1985)
Table III-2 Parameters of thermal comfort Parameters Personal 1. Activity level 2. Clothing Individual Characteristics 3. Expectation Environmental Conditions and Architectural Effects 4. Air temperature 5. Radiant temperature 6. Humidity 7. Air speed
It is possible to synthesise various parameters into a thermal index (Table III- 3).
Researcher Fazia Ali Toudert states that: (Toudert, 2005)
―A rational definition relates thermal comfort to energy gains and losses and describes the state of comfort as satisfied when the heat flows to and from the human body are in equilibrium. This is achieved when the body data, i.e. skin temperature, sweat rate and/or core temperature, are within a range of comfort. These data are partly governed by the thermo-physiological regulations of a human being. Assessing the human thermal comfort is not a recent issue and is not obvious. People have always been concerned by their well being and looked for methods to quantify their sensation of cold or heat). The thermal environment and its impact on a human body cannot be described as a function of one single factor (e.g. Ta) because the body does not possess individual sensors for each factor and consequently feels the thermal environment as a whole. A thermal index is based on the same idea: it combines several factors (e.g. Ta, RH, v, radiation fluxes, etc.) into a single variable which sums up their simultaneous effects on the sensory and physiological responses of the body.‖
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Table III-3 Selected thermal comfort indices for indoors and outdoors (Fanger 1970, Givoni 1976, and ASHRAE 2001a)
“A large number of thermal indices exist …, most of them share many common features and can be classified in two groups: empirical or rational. These indices are well documented and some of them are exemplarily listed in Table III- 3. The indices of the former group, generally developed earlier, are based on measurements with subjects or on simplified relationships that do not necessarily follow theory. These are often limited to the estimation of the combined effect of air temperature, air humidity and air speed on people in sedentary activity. Rational indices are more recent, promoted by the lately development of computing techniques, and rely on the human energy balance. Here, the heat transfer theory applies as rational starting point to describe the various
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sensible and latent radiation flux exchanges, together with some empirical expressions describing the effects of known physiological regulatory controls.”
“The comfort equation proposed by Fanger is probably the most well-known application of the human energy balance. For outdoor conditions, it is necessary to incorporate the solar and terrestrial radiation fluxes. … PET calculated by MEMI (Munich Energy Model for Individuals) was especially developed for outdoor environments; see Table III- 2 for definitions’ comparison. … Theoretically, PET have the advantage on Predicted Mean Vote (PMV) in that it takes into account the thermoregulations of a human body and are therefore more accurate for extreme conditions (typically outdoors).”
Referring to Toudert‘s description, the study adopts the use of PET (Höppe, 1999 and 2002) (Mayer and Hoppe, 1987) as the heat balance model understanding of air movement for human thermal comfort. The model has already been adopted when the technical note titled ―Technical Input - Methodologies and Findings of User‘s Wind Comfort Level Survey‖ was prepared.
Utilising the PET mathematical formulation, the beneficial effects of wind for thermal comfort can be analysed (Figure III- 6). In short, for weak wind condition of 0.5 to 1.5 m/s, it can be stated that the benefit is approximately 2 degrees per 1 m/s. This is in line with the experimental results in section 1.1.2 of this report above. It should be noted that the experimental and the model understanding of air movement for human thermal comfort is similar.
Figure III-6 PET vs. wind
1.1.4 Wind criterion to be used
Internationally, when formulating their various thermal indices, researchers like Fangers, Gagge, Jendritzky, Pickup, de Dear and Höppe all used mean wind speed as the basis for
School of Architecture, CUHK Page 336 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT calculating the convective effects of air movement to human body energy balance , (Pickup and de Dear, 1999) (Höppe, 1984, 1993, 1999 and 2002). Mean wind speed has been found to be the most direct and appropriate parameter to be used.
When summarising the COST ACTION C1434 study, Professor Baker noted that,
―At more normal wind speed levels, pedestrian wind comfort criteria are usually based on one or more combinations of wind speed and the associated probability of exceedance. At the lowest level wind speeds, there is a requirement that for a certain percentage of the time certain minimum wind velocities should be exceeded.‖
The view was echoed by Professor Stathopoulos (2004), as he noted that,
―Pedestrian level winds can be described quite adequately in terms of mean velocities in the presence and absence of a new building within a specific urban environment. … several major cities require only the satisfaction of certain mean (sustainable) speeds with a specified probability of exceedance.‖
Therefore, the hourly mean wind speed coupled with the probability of occurrence or exceedance is recommended to be used as the fundamental basis for the urban air ventilation performance criterion of Hong Kong. This may be stated as: (Fangers, 1970) (Gagge et al, 1971) (Gagge et al, 1986), (Jendritzky and Nübler, 1981)
In a specified period, for X % of the time, the hourly mean wind speed of Y m/s is exceeded.
PART III(A)-2 USER THERMAL COMFORT SURVEYS The ―Technical Input - Methodologies and Findings of User‘s Wind Comfort Level Survey‖ (User Thermal Comfort Surveys) and the findings are summarised below:
1) Urban outdoor thermal comfort is important for people using outdoor spaces. The main objectives of the User‟s Wind Comfort Level Survey are i) to understand the outdoor thermal comfort requirements of Hong Kong people and ii) to find out the range of comfortable wind environment required by them.
2) The methodology of the User‟s Wind Comfort Level Survey includes: i) micro-meteorological measurement and ii) user questionnaire survey. The data were collected throughout 2006-2007 to capture a wide range of
34 Franke, J., Hirsch, C., Jensen, A. G., Krus, H. W., Schatzmann, P. S., Miles, S. D., Wisse, J. A. and Wright, N. G. (2004). Recommendations on the Use of CFD in Wind Engineering. COST Action C14: Impact of Wind and Storm on City Life and Urban Environment, Brussels.
School of Architecture, CUHK Page 337 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT weather conditions of Hong Kong. 2702 completed interviews have been conducted.
3) In line with international practice, the Physiological Equivalent Temperature (PET) comfort model is used to analyse the results. The model allows a synergetic understanding of human thermal comfort based on various environmental and physiological inputs, like air temperature, radiation, humidity, clothing, and so on. The PET value that one expresses a neutral (neither cool nor warm) thermal sensation (nTS) is known as the neutral PET (nPET).
4) The summer months are considered more critical for urban thermal comfort in Hong Kong, the summer dataset is a key focus of analysis. HKO long-term air temperature data have been used to establish the nPET under typical HK summer condition. Based on the survey, it is established that the summer mean nPET is 28.1℃, and around 50% of the surveyed subjects would express nTS when PET is in the range of 27-29℃; 32% will express thermal sensation of “too warm”, 13% “hot” and 4% “very hot”. For the summer nPET = 28.1℃, for example, under an air temperature of 27.9℃, relative humidity of 80%, and a person standing or walking under shade in streets or urban spaces, in the summer months, a light air of 0.9-1.30 m/s, depending on the strength of Tmrt, would be thermally comfortable.
PET = 28.1°C Ta (°C) Tmrt (°C) V (m/s) 28 0.2 30 0.6 32 0.9 34 1.3 27.9 36 1.8 38 2.3 40 2.9 42 3.5 44 4.1 RH=80% Clo=0.3 MET=1
Climatic requirements when neutral PET=28.1℃ (see also PART III-Appendix 2 for further data when Ta = 28.)
5) Due to thermal adaptation, the winter nPET is lower, at 14.6℃ under HK typical winter conditions. Around 70% of the surveyed subjects would express nTS when PET is in the range of 14-16 ℃. Even at PET of 13℃ or lower, only 42% of the surveyed subjects express TS=-1 or lower. For Hong Kong‟s typical mean winter air temperature of 16.3 ℃, assume Tmrt of 17℃ (in shade), wind speed needs to exceed 3 m/s to result in PET of 13℃ or lower. Hence, save some exposed conditions in very windy days, thermal discomfort due to wind in the winter months is unlikely to be an issue.
6) For urban air ventilation, the survey results suggest that providing light air in summer is important and beneficial for the hot summer months of Hong Kong. It is important that the city is planned to optimise air ventilation. Apart from air ventilation, to further improve urban thermal comfort, it is useful i) to provide more shading areas in the city and ii) to provide greeneries, such as planting more trees. They help to reduce solar radiation gains and lower air temperature.
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PART III(A)-3 THE NEED OF WIND FOR URBAN THERMAL COMFORT
Based on the user thermal comfort surveys, for urban air ventilation in the summer months of Hong Kong, it is prudent to recommend light air 35 in the order of 0.9-1.30 m/s depending on the strength of Tmrt.36
It can be noted that Tmrt of the urban environment varies widely (Figure III-7). Within the urban built environment in Hong Kong, surrounded by man-made materials and surfaces, even under shading, the mean radiant temperature (Tmrt) at the pedestrian level in outdoor spaces in the summer time can be 4 • 6°C higher than the ambient air temperature. Hence,
35 Light air of 1 to 3 mph (0.5 to 1.3 m/s) is as defined in the Beaufort scale.
36 Tablada A et al (2009) conducted field studies in Havana (sub-tropical hot and humid climate) and noted that wind has a beneficial effect to votes of human thermal comfort. When the ambient Ta is around 27.7 degree C, Tmrt ~ Ta, the desirable wind speed is 0.5 to 0.8 m/s. In Hong Kong, Ta is around 28 degree C and Tmrt is some 4-6 degree C above Ta, hence the desirable wind speed needed will be higher.
(0 - comfortable, 1 - comfortably warm, 2 - too warm, 3 - much too warm). Error bars represent the standard deviation.
School of Architecture, CUHK Page 339 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT the study recommends that a mean wind speed 0.9 to 1.3 m/s is a reasonable performance criterion to be considered for Hong Kong‘s urban wind environment when taking into account the Tmrt.
Figure III- 7 Tmrt of HK urban conditions based on summer 2007 non-A/C data of the user survey
A probability of occurrence / exceedance needs to be stated. Ideally, it should be 100% of the time, but this is not realistic under natural conditions. Some researchers on outdoor transient based human comfort studies (Bruse, 2007) have used 70/30 (70%) as their bases; and Murakami have suggested ―50% of the time‖ as a reasonable and convenient % to use (Murakami and Morikawa, 1985) (Murakami et al, 1986) (Ng et al 2004). The study suggests that:
In the summer months of Jun – Aug, the median “hourly mean wind speed” should be >= 1 m/s be the generic urban air ventilation performance criterion for urban thermal comfort in Hong Kong. The generic criterion stated here is based on human thermal comfort of inhabitants of Hong Kong and is therefore not location specific. This human-physiological understanding has been the basis of the Hong Kong Urban Climatic Map and has been applied throughout the study (based on UCAn-Map Class 3-4 urban thermal comfort condition as the basis).
School of Architecture, CUHK Page 340 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT
PART III(A)-4 FURTHER URBAN CLIMATIC UNDERSTANDING OF URBAN THERMAL COMFORT It is useful to bear in mind the parameters of human heat balance, with wind or air movement over human body being one of four key environmental parameters. It is most important to consider this in the hot and humid summer months of sub-tropical climate conditions. Given the same ambient air temperature and relative humidity, the lack of wind can be somewhat compensated with the lowering of the mean radiant temperature (Tmrt).
Equation 1 summarises the Physiological Equivalent Temperature (PET) formulation in ―light air‖ urban air ventilation conditions (0.5 For example, based on the understanding in Table III-4, it is possible to accept a lower wind speed if Tmrt can be kept to 2-4 degrees (instead of 4-6 degrees) above Ta. That is to say, it is possible to mitigate the ill-effects of areas with slightly lower wind velocity ratio and hence lower urban air ventilation availability at the pedestrian level by extensive tree planting (hence providing shading) and greenery over larger surface area (hence reducing sunlight reflection). Table III-4 A tabulation of PET, Ta, Tmrt and v PET = 28.1°C Ta (°C) Tmrt (°C) V (m/s) 28 0.2 30 0.6 32 0.9 34 1.3 27.9 36 1.8 38 2.3 40 2.9 42 3.5 44 4.1 RH=80% Clo=0.3 MET=1 Task 1 – the urban climatic map (Figure III-8) of the study has also incorporated this key understanding. Urban climatically speaking, Thermal Load (negative thermal comfort impact) can be alleviated by better Dynamic Potential, which provides possible positive thermal comfort contributions (Table III-5). Greenery is also a positive contribution amongst the School of Architecture, CUHK Page 341 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Thermal Load factors.37 It has been calculated that greenery at an district based area average of 33.3% (1/3), especially with tree planting, may have a beneficial effect of lowering the thermal load class of the Hong Kong UC-AnMap by 1 class, thus lowering the impact on thermal stress. Figure III-8 The Hong Kong Urban Climatic Analysis Map (2009 version) It has been calibrated that Class 3 and 4 of the UCMap represent the nPET (neutral thermal comfort) conditions under typical average Hong Kong summer conditions (Refer to Part I- WP1 for details). 37 Based on the PET understanding, it can be stated that: in weak wind condition of 0.5 to 1.5 m/s the benefit of 1 m/s increase in wind speed is approximately equal to 2 degrees reduction in air temperature in terms of human thermal sensation. In short, it is possible to balance for example the benefits of providing greening to lower urban air temperature to compensate and mitigate the ill- effects of weak air ventilation for urban human thermal comfort. School of Architecture, CUHK Page 342 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Table III-5 Description of the 8 urban climatic classes of the draft UC-AnMap Approximate Impact on Thermal Comfort Class Urban Climatic Class PET Difference (When Ta is 28⁰C) 1 Moderately negative Thermal Load -2 Moderate cooling and Good Dynamic Potential 2 Slightly negative Thermal Load and -1 Slight cooling Good Dynamic Potential 3 Low Thermal Load and Good 0 Neutral Dynamic Potential Some Thermal Load and Some 4 +1 Slight warming Dynamic Potential Moderate Thermal Load and Some 5 +2 Moderate warming Dynamic Potential Moderately High Thermal Load and 6 +3 Moderately strong warming Low Dynamic Potential High Thermal Load and Low 7 +4 Strong warming Dynamic Potential Very High Thermal Load and Low 8 +5 Very strong warming Dynamic Potential Note: 1 moderately negative Thermal Load due to higher altitude and adiabatic cooling, and greenery and trans-evaporative cooling 2 slightly negative Thermal Load due to vegetated slope and trans-evaporative cooling 3 to 8 various classes of warming impact due to increasing Thermal Load and decreasing Dynamic Potentials Based on the Hong Kong UC Map classification and the PET formulation, it can be resolved that the classes can have the following parametric understanding (Table III- 6). Hence, for example, for Class 7 areas, to improve it urban climatically, one may wish to improve air ventilation from 0.3 m/s to 0.6 m/s or better still to 1.0 m/s so as to bring it down to Class 6 and 5 respectively. Furthermore, by further lowering the Ta from 30 degree C to 29 degree C – by introducing greening – the area will have UCMap Class 5 and 4 respectively. Table III-6 A parametric understanding of PET based on the HK UC-AnMap PET (deg C) UCMap Class Ta (degree C) Tmrt (degree C) V (m/s) 28 3 28 Ta+4 1 29 4 29 Ta+4 1 30 5 29 Ta+4 0.6 31 6 30 Ta+4 0.6 32 7 30 Ta+4 0.3 33 8 31 Ta+4 0.3 In addition, apart from the cooling benefits of human bodies for thermal comfort, wind in the urban environment can also have the potential to alleviate urban heat island (UHI) effect. Researchers Kim and Baik (2002) have suggested that with a wind speed of 0.8 m/s or above, School of Architecture, CUHK Page 343 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT UHI will start to decrease. Morris et al (2001) reported that the UHI is approximately the fourth root of both the wind speed and cloud cover. Klysik and Fortuniak (1999) also reported a lowering of UHI during daytime when wind is around 2 m/s. Researchers of Beijing Meteorological Office have also suggested using 1 m/s as the benchmark for the purpose of urban pollution dispersion. (Beijing, 2004). They also use the area coverage of weak wind regions as a criterion for assessment. Summing up the understanding outlined above, therefore it is suggested that the ―desirable‖ minimum urban wind performance criterion be stated as follow: Summer (1 Jun – 31 Aug) median hourly mean 38 wind speed 1 m/s And Annual median hourly mean wind speed 1 m/s PART III(B): BENCHMARKING STUDIES PART III(B)-1 INTRODUCTION The urban air ventilation performance criterion is ―desirable‖ from a human physiological point of view. It is important to test its applicability given the urban ―developed‖ context of Hong Kong. To achieve that, wind tunnel tests of 20 areas have been conducted. The idea is to investigate the existing wind environment of our city and compare it with the desirable urban wind performance. PART III(B)-2 WIND TUNNEL TEST RESULTS The Study has conducted wind tunnel tests for 10 pairs of 20 areas. A summary of their VRw and Vp (wind speed at pedestrian level) annually and in the summer months can be found in Figure III- 9 and Figure III- 10. 38 A steady state solution of CFD results can be regarded as equivalent to hourly mean wind speed. School of Architecture, CUHK Page 344 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-9a Summary of summer VRw School of Architecture, CUHK Page 345 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-9b Summary of annual VRw School of Architecture, CUHK Page 346 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-10a Summary of summer wind speed(Vp) School of Architecture, CUHK Page 347 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-10b Summary of annual wind speed(Vp) School of Architecture, CUHK Page 348 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT A summary understanding of the benchmarking study is also presented in Table III-7 and 8. The data is extracted from the benchmarking data report (see PART III-Appendix 3). For each test area, the VRw and the corresponding Vp in summer and annually are summarised. The percentages of test points of the test area with the median hourly mean wind speed < 1 m/s annually and in the summer months are summarised in Figure III-11. In the summer months, only test areas that are relatively exposed and nearer to the waterfront (for example Shatin and Sam Po Kong) would have less than 25% of its test points with the median hourly mean wind speed less than 1 m/s. Annually, the denser inland areas of Sheung Wan, Causeway and Tsim Sha Tsui would have more than 75% of the test points with the median hourly mean wind speed less than 1 m/s. This indicates their relatively poor existing urban ventilation conditions. The data of the benchmarking tests are further tabulated in Table III- 8 to 9 and shown in Figures III - 12 to 21. School of Architecture, CUHK Page 349 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Table III-7a A summary of the benchmarking study (ratio of Test point with median hourly mean Vp < 1 m/s) School of Architecture, CUHK Page 350 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Table III-7b A summary of the benchmarking study (ratio of Test point with median hourly mean Vp < 0.6 m/s) School of Architecture, CUHK Page 351 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-11 A summary of percentage of test points with median hourly mean wind speed < 1 m/s (annual situation (top) and summer situation (bottom)) School of Architecture, CUHK Page 352 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT The Vp of the 10 test areas is summarised in Figure III-10. They highlight conditions where the median hourly mean wind speed Vp > 1 m/s is difficult to achieve under the exisiting urban morphology. Table III-8 Summary of the annual median hourly mean wind speeds (50% probability of exceedance) (Zone A & B) School of Architecture, CUHK Page 353 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Table III-9 Summary of summer median hourly mean wind speeds (50% probability of exceedance) (Zone A & B) School of Architecture, CUHK Page 354 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-12 Test Area 1-Tsim Sha Tsui (Top: Annual; Below: summer) School of Architecture, CUHK Page 355 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-13 Test Area 2-Mong Kok (Top: Annual; Below: summer) School of Architecture, CUHK Page 356 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-14 Test Area 3-Sheung Wan (Top: Annual; Below: summer) School of Architecture, CUHK Page 357 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-15 Test Area 4-Causeway Bay (Top: Annual; Below: summer) School of Architecture, CUHK Page 358 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-16 Test Area 5-Tsuen Wan (Top: Annual; Below: summer) School of Architecture, CUHK Page 359 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-17 Test Area 6-San Po Kong (Top: Annual; Below: summer) School of Architecture, CUHK Page 360 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-18 Test Area 7-Tuen Mun (Top: Annual; Below: summer) School of Architecture, CUHK Page 361 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-19 Test Area 8-Sha Tin (Top: Annual; Below: summer) School of Architecture, CUHK Page 362 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-20 Test Area 9-Tseung Kwan O (Top: Annual; Below: summer) School of Architecture, CUHK Page 363 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-21 Test Area 10-Wong Chuk Hang (Top: Annual; Below: summer) School of Architecture, CUHK Page 364 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART III(B)-3 REMARKS ON THE BENCHMARKING TESTS RESULTS Through the wind tunnel benchmarking studies, the desirable minimum urban wind performance criterion especially in the summer months is shown to be difficult to achieve in the urban context of Hong Kong given its existing high urban density, narrow streets, tall and bulky buildings and large podia. Based on the results of the wind tunnel benchmarking studies, 16 out of the 20 benchmarking areas have a majority of the test points with wind speed below 1m/s in the summer months. Four areas in San Po Kong, Wong Chuk Hang and Shatin have attained wind speed higher than 1m/s for most of the test points, which is mainly attributed to lower building densities, higher urban permeability and greater proximity to openness. In contrast, the 16 non- compliance areas are characterised by narrow streets and developments that are high in density, tall and bulky with large podium. Hong Kong is actually well endowed with wind (see table below). The key is to optimise it through better urban and building designs. * Thus, any attempt to state a ―desirable‖ urban wind performance criterion to address the need for urban human thermal comfort would be practically difficult to achieve in the short run. For practical consideration, the desirable urban wind performance criterion can at best be stated as ―a target‖ to be achieved eventually, or as ―a reference towards better design‖ at this moment. School of Architecture, CUHK Page 365 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART III(B)-4 POSSIBLE IMPACT OF THE MISMATCH When examining the results of the wind tunnel benchmarking studies, the result illustrates that in the urban areas of Hong Kong, the existing urban wind performance is, in general, ―poor‖ except in unobstructed areas nearer to the waterfront and exposed areas. Of the 20 urban areas that we have examined, 16 of them would not be conducive to healthy living in air ventilation terms. People may be suffering in terms of thermal discomfort and, possibly heat stress (Figure III- 22). Figure III-22 News and recent studies on heat-stress-related mortality (Source: E.Y.Y. Chan, W.B. Goggins, J.J. Kim, A study of intracity variation of temperature-related mortality and socioeconomic status among the Chinese population in Hong Kong. Journal of Epidemiol Community Health (2010) DOI:10.1136/jech.2008.085167 and Leung, Y. K., K. M. Yip, and K. H.Yeung (2008) Relationship between thermal index and mortality in Hong Kong, Meteorological Applications 15: 399–409.) Figure III-23 Increasing trend of very hot days and very hot nights in Hong Kong from 1890- 2000 (Increase of Very Hot Days and Very Hot nights over the years indicates that our urban environmental is getting hotter and hotter due to urban heat island and lack of urban ventilation. ) Local public health researchers have found that heat stress is becoming an issue in urban Hong Kong. Higher urban temperature and weaker urban air ventilation can cause discomfort, thermal stress, and worse still, heat stress related mortality. In addition, the number of very hot days (day time air temperature exceeding 33 ℃) and very hot nights (night time air temperature exceeding 28 ℃) will increase drastically due to higher Urban School of Architecture, CUHK Page 366 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Heat Island Intensity (Table III-10). As heat stress related mortality is directly related to ―temperature elevation intensity‖, heat wave ―duration‖ and heat wave ―frequency‖, the problem can be severe if left unattended (Figure III-22). Table III-10 The number of Very hot days can increase from 11 days to 97 days per year with an urban heat island intensity of 3 ○C. In Hong Kong, some urban areas are already experiencing an UHI of 4 to 5 degrees. (Source: Ng, E., (2009) Wind and Heat Environment in Densely Built Urban Areas in Hong Kong, (invited paper) A special issue on Wind Disaster Risk and Global Environment Change, the Association of International Research Initiatives for Environmental Studies (AIRIES), Journal of Global Environmental Research, Vol.13, No.2, 2009, pp169-178.) In addition, it has been estimated that energy use of buildings can increase by 15% if the outdoor air temperature rises by 3 oC (Table III-11). Table III-11 Impact of urban temperature on energy consumption of Hong Kong (Fung et al, Energy 31 2623-2637,2006). If quality of life is to be improved, a determined action is needed to reverse the trend of UHI deterioration. In this regard, the Study has now provided scientific evidence to guide such School of Architecture, CUHK Page 367 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT actions. ―Business as usual‖ is clearly not an option and current practice would need to be revisited. All in all, it is now high time to consider the urban climatic environment of Hong Kong in a balanced manner. The following recommendations are the minimum that needs to be done to address the critical issue at hand. School of Architecture, CUHK Page 368 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART III(C): WIND PERFORMANCE CRITERION PART III(C)-1 THE WIND PERFORMANCE CRITERION FOR HONG KONG 1.1 A practical approach Bearing in mind the difference in terms of providing a desirable urban air ventilation environment for Hong Kong and the practical difficulties of fully achieving it, it is suggested that a best practice approach be adopted. This would allow projects to aspire and move in the right direction in terms of development intensity, building height, and building disposition for attaining better urban air ventilation. Hence, the recommended Wind Performance Criterion comprise two limbs, i.e. the Wind Performance Requirement and the Alternative (Prescriptive) Approach. Wind Performance Requirement: 80% of all test points inside the assessment area as defined in the AVA Technical Circular have: Annual median hourly mean wind speed ＞＝ 1 m/s AND Summer median hourly mean wind speed ＞＝ 1 m/s And 95% of all test points inside the assessment area as defined in the AVA Technical Circular have: Annual median hourly mean wind speed ＞＝ 0.6 m/s AND Summer median hourly mean wind speed ＞＝ 0.6 m/s When it is demonstrated that the Performance Approach cannot be reasonably and practically achieved, due to the exisiting urban building morphology, such as high urban density, narrow streets, exisiting bulky buildings and large podia, and hence the limited wind available, the project proponent may be allowed to adopt the Alternative (Prescriptive) Approach. School of Architecture, CUHK Page 369 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Alternative (Prescriptive) Approach: (prescriptive Taking into account the Study‘s analysis of various factors mitigating design affecting urban climatic situation and the PNAP APP-152, an measures) alternative (prescriptive) approach requiring the following mitigation design measures are formulated: Ground coverage of no more than 65% Building (tower block) permeability as per PNAP APP-152; Building setback requirement near narrow street as per PNAP APP-152; and Greenery (preferably tree planting) of not less than 30% for sites larger than 1 ha, and 20% for sites below 1 ha at lower levels, prefereably at grade. Sites smaller than 1,000m² are exempted. Remarks: The stated design features are to improve the urban climatic condition by lowering the ground coverage and increasing the airspace nearer to the ground level and by providing greening and tree shades. They are prescriptive design requirements and not inter-tradable. The Performance Approach basically applies the desirable outdoor thermal comfort environment as the basis for consideration. Noting that in some cases there will be isolated test points that cannot meet the wind performance requirement, only 95% of the test points will, therefore, be considered. In addition, taking into account the practical consideration that there are always some isolated wake areas behind buildings where the desirable air ventilation performance is difficult to achieve, the Wind Performance Requirement allows a further 15% (total 20%) of the test points to fall below the reasonably desirable wind performance from 1 m/s to 0.6 m/s. It is advisable that project proponent can further consider reducing the Tmrt (which related to surface temperature of the surroundings) of the areas surrounding these test points as so to mitigate some of the possible ill-effects of thermal discomfort. Greening on both the paved surfaces and on the vertical surfaces of buildings near the pedestrian level are useful measures. To demonstrate the fulfilment of the Wind Performance Requirement, an AVA detailed study has to be conducted. The Alternative (Prescriptive) Approach is proposed to cope with circumstances (mainly in old urban areas) where the Wind Performance Requirement has been demonstrated to be practically impossible to achieve due to the existing building morphology. The Alternative (Prescriptive) Approach is based on the same scientific understanding of the UC-Map. It relies on the same area average parametric understanding that if ALL the building sites in the area follow the same prescriptive approach, the ―collective and culminated overall (thermal + dynamic) urban climatic condition‖ would be comparable to that under the Wind Performance Requirement – by lowering the ground coverage and School of Architecture, CUHK Page 370 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT increasing the airspace nearer to the ground level and by providing greening and tree shades. The scientific understanding is summarised in Figure III-24 to 32. 1.2 Parametric Tests Several parametric tests had been done to evaluate the impact of the development parameters on the urban climate and air ventilation on ar area basis. The parametric tests are documented from Figure III - 24 to 32. Parametrically and on an area average basis, by reducing the site ground coverage of buildings to 65%, adding tree planting at grade to 30%, and allowing building permeability to about 25%, the synergetic effects may reduce the PET by 2 degrees. It must be highlighted that the understanding is built on the concept that: if everyone does their share collectively and eventually, the urban environment would improve for the better in urban climatic terms. The recommended design measures are prescriptive design requirements and are not inter- tradable. Should a project proponent wishes to reduce the ground coverage to only 80% instead of the required 65%, he/she can ONLY do so by subjecting the revised design to a detailed AVA test to satisfy the Wind Performance Requirement. It should be noted that the desired objectives for a better urban environment by optimising Building Separation, Building Setback and Greenery under the Buildings Department‘s newly promulgated PNAP APP-152 ‗Sustainable Building Design Guidelines‘, are largely in line and comparable with the Alternative (Prescriptive) Approach as recommended in this study. School of Architecture, CUHK Page 371 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT VR Figure III-24 Reduction of building ground coverage ground coverage should be under 70% Figure III-25 Reduction of building ground coverage (Source: Ryuichiro Yoshie , Hideyuki Tanakaa and Taichi Shirasawa and Edward Ng, Experimental Study on Air Ventilation in a Built‐ up Area with Closely‐ Packed High‐ Rise Buildings, J. Environ. Eng., AIJ, Vol. 73 No. 627,661‐ 667, May, 2008.) School of Architecture, CUHK Page 372 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-26 Increasing urban permeability (Source: Yim, S.H.L., Fung, J.C.H., Lau, A.K.H., &Kot, S.C.(2009). Air ventilation impacts of the „„wall effect‟‟ resulting from the alignment of high-rise buildings. Atmospheric Environment, 43 (32), 2894–2982.) School of Architecture, CUHK Page 373 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-27 Increasing urban permeability Figure III-28 Increasing urban permeability (Source: Yuan, C. and Ng, E., (2012) Building Porosity for better urban Ventilation – a computational parametric study, Building and Environment, 50, 176-189. doi:10.1016/j.buildenv.2011.10.023) School of Architecture, CUHK Page 374 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-29 Improving urban greenery Figure III-30 Improving urban greenery School of Architecture, CUHK Page 375 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-31 Improving urban greenery School of Architecture, CUHK Page 376 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure III-32 Improving urban greenery (Source: Ng, E., Liang, C., Wang, Y. N. and Yuan, C., (2011). A study on the Cooling Effects of Greening in High Density City: an experience from Hong Kong, Building and Environment. Online 28 July 2011, ISSN 0360-1323, DOI: 10.1016/j.buildenv.2011.07.014.) School of Architecture, CUHK Page 377 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT 1.3 Exemption It is acknowledged that there will be projects of special functional requirements that cannot satisfy the above approaches. As such, the Study recommends that developments with demonstrated functional requirements in terms of building length and/or ground coverage (e.g. infrastructural facilities, transport terminus, sports and civic facilities) may be exempted from implementing the prescriptive mitigating design measures under the Alternative (Prescriptive) Approach subject to the following: the building separation requirement is in full compliance with other buildings on the same site or other parts of the building that are located above such special facilities being exempted, where applicable; a quantitative AVA be conducted to demonstrate that the eventual design option, with all practicable mitigation/improvement measures, has been selected based on a comparison of different design options; and greening and tree planting opportunities have been maximised within the pedestrian zone, preferably at grade and at the part of the site not built over. 1.4 Long Term Improvement It must be highlighted that the ‗practical‘ consideration of allowing an Alternative (Prescriptive) Approach will only slowly improve the overall air ventilation performance of the urban area. Unless most, if not all, projects could fulfil the prescriptive mitigating design measures, the urban air ventilation performance would unlikely reach the desirable standard. PART III(C)-2 IMPLICATIONS Noting the practical difficulties of the urban context of Hong Kong to attain to the desirable urban air ventilation, the Study has recommended a Wind Performance Criterion comprising of the Wind Performance Requirement, Alternative (Prescriptive) Approach and Exemption Clause. This three-pronged approach is considered to be the most practical and flexible way in achieving a better urban climate. The Wind Performance Criterion does not, by itself, impose an impact on development intensity. Instead of area-wide restrictions in development intensities, the remedial mitigating design measures, including those set out in the Alternative (Prescriptive) Approach, specifically target building disposition and design on a site-basis to promote air ventilation in existing problem areas. School of Architecture, CUHK Page 378 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT More generally, the Wind Performance Criterion can provide a useful yardstick for the quantitative formulation of development control parameters and to promote design improvements in the planning process. They also provide a more solid basis for extending the scope of application of AVA currently set out in the Technical Circular and Technical Guide on Air Ventilation Assessment in Hong Kong. To make good use of the Wind Performance Citerion, the administration would need to review the various policy areas including, (i) the categories and stages of development projects that need to undertake AVAs with different levels of detail, (ii) the factors to be taken into account in assessing the needs of AVAs for individual projects, (iii) the suitable set of wind availability data adopted for planning purpose, as well as (iv) the scope and applications of different AVA and related studies (expert evaluation, initial study and detailed study), to be adopted with respect to the latest understanding of the urban climate and wind environment of Hong Kong. In terms of implementation, all advisory, regulatory, and incentive approaches should be reviewed with reference to other parallel green building and sustainable development initiatives being established in Hong Kong. Further investigation in these areas will be carried out when looking into the implementation mechanism for the refined AVA System in Part IV of the Report. The Wind Performance Criterion provides a yardstick for the Hong Kong Government and project proponents to gauge the air ventilation performance of a project proposal. To begin with, it is recommended that the Wind Performance Criterion be implemented through the administrative approach under exisiting developing control mechanisms. At this stage, a legislative approach to implement the Wind Performance Criterion is premature and is not recommended. The Study recommends the Government to: (a) update the current Technical Circular on AVA (No. 01/06) to reflect the refined methodology and the Wind Performance Criterion; (b) continue the current practice of requiring all relevant public projects to conduct AVA at the early planning and design stage and demonstrate acceptability from air ventilation point of view; and (c) widely promote greenery, especially tree planting, in the public realm and open spaces so as to improve the thermal comfort of the urban environment. The Study recommends the private sector to: (a) incorporate appropriate building design to improve urban air ventilation; and School of Architecture, CUHK Page 379 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (b) demonstrate air ventilation acceptability and adopt mitigating design measures in new developments. All in all, it must be highlighted that the city belongs to everyone in Hong Kong. As such, both the public and the private sector must do their fair share, so that through concerted efforts, the urban living environment in Hong Kong would gradually improve for the better and to the benefit of our future generations. PART III(C)-3 REVIEW DURATION AND MECHANISM 3.1 Interim review It is recommended that an interim review of Hong Kong‘s Wind Performance Criterion be conducted 5 year after its promulgation and practical application. The key purpose is to evaluate if the criterion is ―fit for purpose‖ – i.e. whether it leads to a better urban air ventilation environment. The questions that should be asked at the review stage should include: Is there any need to refine its understanding? Is there any loophole in implementing the criterion? Is it difficult to use and apply? Does it allow for design flexibility and innovative ideas? Is it yielding a desirable outcome? Is there any room for further improvement? It is proposed that an expert committee led by the Planning Department be established for the preliminary review. Membership of the committee should include representatives from academia, the trade, professional organisations and government departments. The committee can formulate its own detailed working procedure. One suggestion is as follows: (a) Correlate the designs that have considered/applied the criterion, note the feedback from the responsible professionals, evaluate the performance of the designs, and evaluate the design features and mitigation measures; (b) Conduct site visit and project specific mini-user surveys to yield representative quantitative data; and (c) Expertly examine the information and propose refinements, if necessary. The Planning Department can organise a round of public consultation exercise to explain the proposed refinements and to gauge the public response. School of Architecture, CUHK Page 380 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT 3.2 Main review Inevitably, the expectations and aspirations of the Hong Kong people change over time. It is recommended that a major review of Hong Kong‘s Wind Performance Criterion be conducted at 10-year intervals. The review is to: (a) Factor in considerations of habitual changes, needs and aspirations of the Hong Kong people. This can be achieved with a new round of user thermal comfort survey. (b) Factor in new understanding of scientific knowledge. This can be achieved using the latest human thermal comfort model and analytical techniques. (c) Factor in new information and international standards as they become available. This can be achieved with desktop study and literature review. (d) Accommodate to new agendas and issues, e.g. the need to factor in climate change, new understanding of heat waves, heat spells and other aspects of urban living. This can be achieved by feeding in the latest climatic information to new climate change based models. It is also proposed that an expert committee led by the Planning Department be established for the main review. Membership of the committee should include representatives from academia, the trade, professional organisations and government departments. It is desirable to include international experts within the expert committee. The committee can formulate its own detailed working procedure. One suggestion is as follows: (a) Conduct a second round of expert review similar to the preliminary review. (b) Conduct desktop literature studies and research on the latest international standards and practices. (c) Conduct a new round of user survey using more up to date research techniques and models. Re-compute the desirable urban Wind Performance Criterion physiologically. (d) Examine the information and identify the need for change and refinements. (e) Propose a new set of urban Wind Performance Criterion as appropriate. The Planning Department can organise a round of public consultation to explain the proposal and to gauge the public response. School of Architecture, CUHK Page 381 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART III(C)-4 FURTHER STUDIES 4.1 Site Wind Availability Study It is recommended that the Planning Department considers generating a set of site wind availability data to standardise the information source for conducting AVA in compliance with the Wind Performance Criterion. School of Architecture, CUHK Page 382 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART III: APPENDICES School of Architecture, CUHK Page 383 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 1: PHYSIOLOGICALLY EQUIVALENT TEMPERATURE Physiologically Equivalent Temperature (PET) Since the 1960s, heat balance models of the human body have become more and more accepted in the assessment of thermal comfort. The basis for these models is the human energy balance equation. One of the first heat balance models is the comfort equation defined by Fanger (1972). One decade later, Jendritzky et al. (1981 & 1989) managed to make Fanger‘s approach applicable to outdoor conditions by assigning appropriate parameters to adjust the model to cater for the much more complex outdoor radiation conditions. This approach, which is also known as the ―Klima Michel Model‖, is now increasingly being applied. Since this model was designed only to estimate an integral index for the thermal component of the climate and not to represent a realistic description of thermal body conditions, it is able to work without the consideration of fundamental thermo-physiological regulatory processes. For example, in Fanger‘s approach the mean skin temperature and sweat rate are quantified as ―comfort values‖, being only dependent on activity and not on climatic conditions (Höppe 1999). More universally applicable models take into account all basic thermoregulatory processes, like the constriction or dilation of peripheral blood vessels and the physiological sweat rate (Höppe 1993, 1999). They enable the user to predict ―real values‖ of thermal quantities of the body, i.e. skin temperature, core temperature, sweat rate or skin wetness. The ―Munich energy balance model for individuals‖ (MEMI) (Höppe 1993) is one such example of a thermo-physiological heat balance model. It is the basis for the calculation of the physiologically equivalent temperature (PET). In detail the MEMI model is based on the energy balance equation (9.1) for the human body: Where, M is the metabolic rate (internal energy production), W is the physical work output, R is the net radiation of the body, C is the convective heat flow, ED is the latent heat flow to evaporate water diffusing through the skin (imperceptible perspiration), Ere is the sum of heat flows for heating and humidifying the inspired air, ESw is the heat flow due to evaporation of sweat, and S being the storage heat flow for heating or cooling the body mass. The individual terms in this equation have positive signs if they result in an energy gain for the body and negative signs in the case of an energy loss (M is always positive; W, ED and Esw are always negative). The unit of all heat flows is in Watt (Höppe 1999). School of Architecture, CUHK Page 384 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT The individual heat flows in Eq. 9.1, are controlled by the following meteorological parameters (VDI, 1997b; Höppe 1999): – Air temperature: C, ERe – Air humidity: ED, ERe, ESw – Wind velocity: C, ESw – Mean radiant temperature: R Thermo-physiological parameters are required in addition: – Heat resistance of clothing (clo units) – Activity of humans (in Watt) The human body does not have any selective sensors for the perception of individual climatic parameters, but can only register (by thermoreceptors) and make a thermoregulatory response to the temperature (and any changes) of the skin and blood flow passing the hypothalamus (Höppe 1993, 1999). These temperatures, however, are influenced by the integrated effect of all climatic parameters, which are in some kind of interrelation, i.e. affect each other. In situations with less wind speed, for instance, the mean radiant temperature has roughly the same importance for the heat balance of the human body as the air temperature. At days with higher wind speeds, air temperature is more important than the mean radiant temperature because it dominates the increased enhanced convective heat exchange. These interactions are only quantifiable in a realistic way by means of heat balance models (VDI, 1997b; Höppe 1999). PET is defined to be equivalent to the air temperature that is required to reproduce in a standardised indoor setting and for a standardised person the core and skin temperatures that are observed under the conditions being assessed (VDI, 1997b; Höppe 1999). The standardised person is characterised by a work metabolism of 80 W of light activity, in addition to basic metabolism; and by 0.9 clo of heat resistance as a result of clothing. The following assumptions are made for the indoor reference climate: – Mean radiant temperature equals air temperature (Tmrt = Ta). – Air velocity (wind speed) is fixed at v = 0.1 m/s. – Water vapour pressure is set to 12 hPa (approximately equivalent to a relative humidity of 50% at Ta = 20°C). The calculation of PET includes the following steps: – Calculation of the thermal conditions of the body with MEMI for a given combination of meteorological parameters. School of Architecture, CUHK Page 385 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT – Insertion of the calculated values for mean skin temperature and core temperature into the model MEMI and solving the energy balance equation system for the air temperature Ta (with v = 0.1 m/s, VP = 12 hPa and Tmrt = Ta). Finally the resulting air temperature is equivalent to PET. PET allows the evaluation of thermal conditions in a physiologically significant manner. In this respect, Matzarakis and Mayer (1996) transferred ranges of Predicted Mean Vote (PMV) for thermal perception and grade of physiological stress on human beings (Fanger 1970; Mayer 1993) into corresponding PET ranges. They are valid only for the assumed values of internal heat production and thermal resistance of the clothing. It is worth mentioning that the VDI-guideline 3787 part 2 ―methods for the human- biometeorological evaluation of climate and air quality for urban and regional planning, part I: climate―(VDI, 1997b) recommends the application of PET for the evaluation of the thermal component of different climates to emphasize the significance of PET further. This guideline is edited by the German Association of Engineers (‗Verein Deutscher Ingenieure‘ (VDI)). From Andreas Matzarakis and Bas Amelung, Physiological Equivalent Temperature as Indicator for Impacts of Climate Change on Thermal Comfort of Humans, in M. C. Thomson et al. (eds.), Seasonal Forecasts, Climatic Change and Human Health. 161 © Springer Science + Business Media B.V. 2008 School of Architecture, CUHK Page 386 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 2 : FURTHER UNDERSTANDING OF PET 28oC RayMan 1.2 © 2000 place: Hongkong Horizon limitation: 0.0% sky view factor: 1.000 geogr. longitude: 114°11' latitude: 22°15' timezone: UTC +8.0 h personal data: height: 1.75 m weight: 75.0 kg age: 35 a sex: m clothing: 0.3 clo activity: 80W Ta RH v Tmrt PET PET < 28 28 75 / 80 0.6 28 27 Yes 30 28 Yes 32 28.9 Yes 34 29.9 36 30.9 38 31.8 40 32.9 1.0 28 26.2 / 26.3 Yes 30 27 / 27.1 Yes 32 27.9 / 28 Yes 34 28.8 / 28.9 36 29.8 / 29.8 38 30.7 / 30.8 40 31.7 / 31.7 1.4 28 25.4 Yes 30 26.3 Yes 32 27.1 Yes 34 28 Yes 36 28.9 38 29.8 In sum, Ta = 28, then Tmrt ~ 28-30, if under shade from the sun, and with plenty of trees and grass surfaces around 32-34, if under shade from the sun in an urban area with buildings around 36 or above, partially shaded to fully exposed under the sun. Tmrt can be as high as 40-50 deg C if fully under the strong summer sun of 600-900 W/m2. School of Architecture, CUHK Page 387 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 3 : DATA OF ANNUAL AND SUMMER VRw AND Vp Annual and Summer months VRw and Vp (Vp < 1m/s 50% time highlighted) Test area 1 Tsim Sha Tsui summer Annual Test point VRw Vpw VRw Vpw Test area 1A TSA01 0.14 0.68 0.13 0.90 TSA02 0.10 0.53 0.10 0.75 TSA03 0.05 0.24 0.06 0.44 TSA04 0.10 0.49 0.10 0.67 TSA05 0.06 0.25 0.07 0.41 TSA06 0.14 0.67 0.14 0.94 TSA07 0.14 0.65 0.13 0.88 TSA08 0.11 0.54 0.12 0.90 TSA09 0.09 0.34 0.13 0.73 TSA10 0.10 0.50 0.09 0.60 TSA11 0.12 0.55 0.12 0.69 TSA12 0.13 0.60 0.12 0.87 TSA13 0.13 0.64 0.13 0.86 TSA14 0.19 0.90 0.16 1.04 TSA15 0.18 0.87 0.18 1.24 TSA16 0.13 0.65 0.14 0.99 TSA17 0.09 0.42 0.09 0.66 TSA18 0.14 0.65 0.17 1.19 TSA19 0.13 0.64 0.15 0.99 TSA20 0.14 0.60 0.16 1.14 TSA21 0.16 0.68 0.16 1.02 TSA22 0.12 0.57 0.10 0.74 TSA23 0.10 0.32 0.14 0.87 TSA24 0.11 0.46 0.13 0.80 TSA25 0.12 0.58 0.11 0.81 TSA26 0.06 0.24 0.07 0.44 TSA27 0.04 0.17 0.06 0.36 TSA28 0.10 0.46 0.10 0.74 TSA29 0.13 0.54 0.16 0.96 TSA30 0.13 0.50 0.17 1.16 TSA31 0.05 0.20 0.04 0.25 Test area 1B TSB01 0.10 0.46 0.10 0.77 TSB02 0.06 0.22 0.08 0.63 TSB03 0.10 0.49 0.12 0.91 TSB04 0.12 0.55 0.16 1.08 TSB05 0.07 0.34 0.07 0.50 TSB06 0.16 0.67 0.18 1.26 TSB07 0.19 0.60 0.22 1.40 TSB08 0.18 0.57 0.23 1.50 TSB09 0.17 0.83 0.19 1.37 TSB10 0.16 0.70 0.16 1.15 TSB11 0.09 0.43 0.08 0.61 TSB12 0.11 0.34 0.15 0.89 TSB13 0.10 0.46 0.11 0.83 TSB14 0.14 0.57 0.14 0.87 School of Architecture, CUHK Page 388 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT TSB15 0.18 0.56 0.20 1.17 TSB16 0.09 0.38 0.10 0.63 TSB17 0.15 0.72 0.14 1.01 TSB18 0.09 0.40 0.08 0.45 TSB19 0.23 0.76 0.27 1.54 TSB20 0.09 0.44 0.09 0.68 TSB21 0.08 0.32 0.09 0.48 TSB22 0.15 0.65 0.17 1.28 TSB23 0.15 0.61 0.18 1.19 TSB24 0.15 0.71 0.17 1.22 TSB25 0.14 0.46 0.19 1.08 TSB26 0.12 0.44 0.16 1.01 TSB27 0.10 0.44 0.10 0.70 TSB28 0.08 0.36 0.08 0.60 TSB29 0.14 0.67 0.14 0.99 Test area 1C TSC01 0.13 0.61 0.12 0.83 TSC02 0.12 0.44 0.16 1.08 TSC03 0.10 0.45 0.14 0.98 TSC04 0.06 0.19 0.09 0.66 TSC05 0.13 0.44 0.16 1.17 TSC06 0.11 0.46 0.14 0.98 TSC07 0.13 0.58 0.15 1.11 TSC08 0.19 0.91 0.16 1.05 TSC09 0.18 0.76 0.25 1.66 TSC10 0.11 0.44 0.12 0.79 TSC11 0.15 0.72 0.16 1.10 TSC12 0.12 0.54 0.14 1.05 TSC13 0.14 0.61 0.17 1.23 TSC14 0.16 0.65 0.18 1.34 TSC15 0.18 0.84 0.21 1.34 TSC16 0.14 0.62 0.17 1.07 TSC17 0.15 0.63 0.15 0.98 TSC18 0.16 0.62 0.20 1.24 TSC19 0.10 0.35 0.14 0.82 TSC20 0.04 0.19 0.05 0.34 TSC21 0.18 0.57 0.20 1.29 TSC22 0.26 0.95 0.26 1.47 TSC23 0.12 0.51 0.12 0.79 TSC24 0.12 0.61 0.11 0.80 TSC25 0.09 0.38 0.10 0.63 TSC26 0.18 0.73 0.22 1.58 TSC27 0.17 0.69 0.15 0.93 TSC28 0.11 0.49 0.10 0.65 TSC29 0.24 1.16 0.25 1.67 TSC30 0.13 0.60 0.13 0.77 TSC31 0.26 1.22 0.26 1.67 TSC32 0.29 1.49 0.25 1.69 TSC33 0.17 0.74 0.18 1.11 TSC34 0.24 1.13 0.25 1.63 School of Architecture, CUHK Page 389 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 2 Mong Kok summer Annual Test point VRw Vpw VRw Vpw Test area 2A MKA01 0.21 1.00 0.24 1.56 MKA02 0.14 0.66 0.14 0.91 MKA03 0.20 0.96 0.23 1.47 MKA04 0.09 0.48 0.10 0.70 MKA05 0.17 0.89 0.17 1.17 MKA06 0.09 0.44 0.09 0.66 MKA07 0.11 0.50 0.12 0.88 MKA08 0.17 0.80 0.21 1.30 MKA09 0.13 0.66 0.12 0.81 MKA10 0.13 0.68 0.15 1.06 MKA11 0.17 0.79 0.21 1.31 MKA12 0.14 0.71 0.16 1.14 MKA13 0.23 1.20 0.22 1.64 MKA14 0.14 0.71 0.15 1.03 MKA15 0.20 1.01 0.23 1.56 MKA16 0.09 0.45 0.12 0.83 MKA17 0.14 0.67 0.14 0.98 MKA18 0.10 0.51 0.09 0.62 MKA19 0.09 0.47 0.10 0.70 MKA20 0.17 0.82 0.19 1.22 MKA21 0.15 0.66 0.20 1.26 MKA22 0.10 0.48 0.09 0.60 MKA23 0.11 0.54 0.12 0.85 MKA24 0.21 1.10 0.23 1.51 Test area 2B MKB01 0.11 0.57 0.11 0.81 MKB02 0.12 0.63 0.12 0.76 MKB03 0.13 0.57 0.14 0.87 MKB04 0.21 1.12 0.20 1.50 MKB05 0.09 0.37 0.11 0.75 MKB06 0.09 0.46 0.09 0.66 MKB07 0.12 0.60 0.12 0.90 MKB08 0.17 0.77 0.16 1.08 MKB09 0.11 0.48 0.10 0.62 MKB10 0.13 0.66 0.14 0.94 MKB11 0.15 0.82 0.15 1.06 MKB12 0.12 0.59 0.13 0.82 MKB13 0.10 0.42 0.12 0.80 MKB14 0.21 1.11 0.19 1.36 MKB15 0.13 0.68 0.14 1.01 MKB16 0.04 0.19 0.05 0.37 MKB17 0.12 0.63 0.12 0.84 MKB18 0.26 1.41 0.25 1.84 MKB19 0.11 0.53 0.13 0.93 MKB20 0.22 1.17 0.25 1.76 MKB21 0.29 1.54 0.27 1.95 MKB22 0.28 1.51 0.28 2.04 MKB23 0.17 0.85 0.17 1.06 MKB24 0.21 1.07 0.21 1.52 MKB25 0.36 1.95 0.33 2.32 MKB26 0.22 1.17 0.21 1.58 School of Architecture, CUHK Page 390 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT MKB27 0.23 1.14 0.26 1.82 MKB28 0.12 0.55 0.13 0.86 MKB29 0.09 0.46 0.10 0.71 MKB30 0.08 0.33 0.11 0.71 MKB31 0.06 0.23 0.08 0.53 MKB32 0.18 0.97 0.18 1.30 MKB33 0.15 0.80 0.16 1.14 Test area 2C MKC01 0.15 0.78 0.15 1.09 MKC02 0.13 0.61 0.16 1.15 MKC03 0.13 0.66 0.13 0.95 MKC04 0.15 0.75 0.16 1.13 MKC05 0.15 0.59 0.20 1.39 MKC06 0.10 0.47 0.13 0.95 MKC07 0.18 0.92 0.19 1.40 MKC08 0.21 0.99 0.28 1.91 MKC09 0.09 0.41 0.10 0.68 MKC10 0.08 0.34 0.10 0.63 MKC11 0.30 1.60 0.30 2.16 MKC12 0.11 0.44 0.13 0.72 MKC13 0.15 0.63 0.17 1.11 MKC14 0.19 0.93 0.22 1.43 MKC15 0.18 0.90 0.17 1.23 MKC16 0.12 0.55 0.13 0.78 MKC17 0.12 0.59 0.12 0.87 MKC18 0.07 0.29 0.08 0.49 MKC19 0.14 0.73 0.14 0.99 MKC20 0.09 0.45 0.10 0.69 MKC21 0.09 0.46 0.10 0.73 MKC22 0.20 1.07 0.20 1.44 MKC23 0.07 0.32 0.07 0.48 MKC24 0.11 0.56 0.13 0.94 MKC25 0.21 0.99 0.19 1.32 MKC26 0.10 0.49 0.12 0.83 MKC27 0.12 0.66 0.12 0.89 MKC28 0.09 0.45 0.08 0.61 MKC29 0.24 1.30 0.27 1.93 MKC30 0.13 0.71 0.13 0.95 MKC31 0.28 1.46 0.31 2.21 MKC32 0.26 1.33 0.29 2.00 MKC33 0.12 0.64 0.12 0.82 MKC34 0.38 2.03 0.37 2.57 MKC35 0.28 1.46 0.27 1.99 School of Architecture, CUHK Page 391 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 3 Sheung Wan summer Annual Test point VRw Vpw VRw Vpw Test area 3A SWA01 0.12 0.41 0.16 0.88 SWA02 0.11 0.39 0.18 0.93 SWA03 0.15 0.50 0.19 1.28 SWA04 0.12 0.42 0.15 0.86 SWA05 0.19 0.69 0.25 1.39 SWA06 0.18 0.59 0.23 1.01 SWA07 0.21 0.74 0.29 1.73 SWA08 0.22 0.78 0.30 1.89 SWA09 0.17 0.61 0.23 1.44 SWA10 0.20 0.59 0.24 1.52 SWA11 0.21 0.82 0.26 1.60 SWA12 0.15 0.48 0.22 1.40 SWA13 0.17 0.48 0.28 1.94 SWA14 0.13 0.48 0.16 0.91 SWA15 0.18 0.62 0.26 1.18 SWA16 0.16 0.58 0.23 1.45 SWA17 0.14 0.49 0.18 0.90 SWA18 0.14 0.48 0.15 0.89 SWA19 0.07 0.20 0.11 0.32 SWA20 0.16 0.65 0.16 1.00 SWA21 0.10 0.40 0.10 0.65 SWA22 0.05 0.21 0.06 0.37 SWA23 0.13 0.49 0.12 0.75 SWA24 0.19 0.77 0.19 1.25 SWA25 0.10 0.35 0.08 0.50 SWA26 0.18 0.68 0.15 0.94 SWA27 0.10 0.39 0.10 0.60 SWA28 0.15 0.56 0.19 1.01 SWA29 0.11 0.40 0.12 0.77 SWA30 0.10 0.39 0.11 0.61 SWA31 0.13 0.51 0.12 0.80 SWA32 0.13 0.49 0.15 0.90 SWA33 0.31 1.21 0.32 1.94 Test area 3B SWB01 0.09 0.32 0.07 0.44 SWB02 0.05 0.19 0.05 0.33 SWB03 0.06 0.22 0.07 0.43 SWB04 0.07 0.27 0.06 0.37 SWB05 0.07 0.27 0.07 0.47 SWB06 0.11 0.37 0.10 0.62 SWB07 0.08 0.33 0.08 0.53 SWB08 0.10 0.39 0.10 0.64 SWB09 0.09 0.32 0.08 0.52 SWB10 0.10 0.33 0.08 0.49 SWB11 0.06 0.23 0.07 0.42 SWB12 0.08 0.30 0.08 0.49 SWB13 0.10 0.37 0.09 0.57 SWB14 0.12 0.38 0.10 0.42 SWB15 0.07 0.28 0.07 0.44 SWB16 0.07 0.25 0.06 0.39 SWB17 0.07 0.28 0.08 0.50 School of Architecture, CUHK Page 392 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT SWB18 0.09 0.27 0.07 0.39 SWB19 0.10 0.38 0.10 0.61 SWB20 0.10 0.36 0.09 0.54 SWB21 0.06 0.22 0.06 0.34 SWB22 0.10 0.33 0.09 0.55 SWB23 0.19 0.76 0.20 1.28 SWB24 0.07 0.27 0.07 0.41 SWB25 0.10 0.39 0.10 0.62 SWB26 0.05 0.17 0.04 0.26 SWB27 0.08 0.27 0.06 0.38 SWB28 0.14 0.53 0.13 0.85 SWB29 0.07 0.27 0.07 0.41 SWB30 0.16 0.53 0.15 0.88 SWB31 0.14 0.55 0.14 0.92 SWB32 0.12 0.46 0.12 0.73 SWB33 0.15 0.58 0.15 0.99 SWB34 0.07 0.28 0.07 0.47 SWB35 0.11 0.44 0.12 0.75 SWB36 0.10 0.41 0.11 0.72 SWB37 0.10 0.38 0.11 0.71 SWB38 0.09 0.32 0.09 0.53 SWB39 0.12 0.48 0.13 0.82 SWB40 0.08 0.30 0.09 0.55 SWB41 0.09 0.37 0.10 0.62 Test area 3C SWC01 0.19 0.69 0.22 1.46 SWC02 0.26 0.88 0.36 2.37 SWC03 0.20 0.68 0.25 1.61 SWC04 0.15 0.54 0.22 1.26 SWC05 0.22 0.84 0.20 1.25 SWC06 0.20 0.72 0.17 1.04 SWC07 0.21 0.79 0.24 1.63 SWC08 0.11 0.44 0.13 0.86 SWC09 0.18 0.70 0.19 1.23 SWC10 0.09 0.33 0.09 0.56 SWC11 0.12 0.45 0.12 0.82 SWC12 0.09 0.36 0.10 0.65 SWC13 0.14 0.53 0.15 0.98 SWC14 0.15 0.58 0.17 1.11 SWC15 0.16 0.64 0.16 1.01 SWC16 0.17 0.60 0.24 1.39 SWC17 0.11 0.38 0.17 1.04 SWC18 0.10 0.40 0.13 0.75 SWC19 0.09 0.34 0.10 0.67 SWC20 0.08 0.21 0.06 0.37 SWC21 0.08 0.25 0.09 0.38 School of Architecture, CUHK Page 393 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 4 Causeway Bay summer Annual Test point VRw Vpw VRw Vpw Test area 4A CBA01 0.15 0.35 0.18 1.29 CBA02 0.16 0.36 0.24 1.61 CBA03 0.16 0.36 0.22 1.39 CBA04 0.14 0.27 0.18 0.98 CBA05 0.13 0.31 0.21 1.18 CBA06 0.14 0.30 0.20 1.39 CBA07 0.18 0.48 0.24 1.74 CBA08 0.20 0.50 0.28 1.92 CBA09 0.17 0.37 0.23 1.65 CBA10 0.16 0.42 0.22 1.57 CBA11 0.18 0.43 0.24 1.33 CBA12 0.14 0.26 0.19 1.12 CBA13 0.20 0.45 0.26 1.52 CBA14 0.14 0.35 0.22 1.26 CBA15 0.09 0.18 0.16 0.62 CBA16 0.09 0.16 0.15 0.59 CBA17 0.12 0.30 0.16 1.16 CBA18 0.10 0.23 0.16 0.98 CBA19 0.14 0.36 0.24 1.43 CBA20 0.27 0.76 0.27 1.88 CBA21 0.11 0.31 0.15 0.98 CBA22 0.12 0.35 0.16 0.95 Test area 4B CBB01 0.14 0.38 0.18 1.22 CBB02 0.18 0.50 0.22 1.54 CBB03 0.19 0.51 0.20 1.40 CBB04 0.14 0.36 0.15 1.05 CBB05 0.13 0.34 0.17 1.06 CBB06 0.13 0.32 0.15 1.09 CBB07 0.15 0.41 0.17 1.03 CBB08 0.09 0.23 0.09 0.58 CBB09 0.09 0.23 0.10 0.63 CBB10 0.09 0.19 0.09 0.55 CBB11 0.08 0.22 0.09 0.57 CBB12 0.14 0.39 0.15 0.98 CBB13 0.14 0.38 0.14 0.96 CBB14 0.14 0.35 0.15 0.99 CBB15 0.20 0.54 0.23 1.63 CBB16 0.08 0.21 0.09 0.55 CBB17 0.19 0.49 0.21 1.34 CBB18 0.23 0.63 0.21 1.39 CBB19 0.18 0.44 0.14 0.68 CBB20 0.09 0.21 0.08 0.51 CBB21 0.11 0.24 0.12 0.67 CBB22 0.18 0.39 0.16 0.99 CBB23 0.15 0.42 0.16 1.12 CBB24 0.15 0.39 0.18 1.01 CBB25 0.19 0.52 0.21 1.16 CBB26 0.26 0.72 0.25 1.54 CBB27 0.10 0.29 0.12 0.78 CBB28 0.19 0.60 0.20 1.02 School of Architecture, CUHK Page 394 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT CBB29 0.17 0.49 0.17 1.04 CBB30 0.23 0.68 0.25 1.61 CBB31 0.18 0.43 0.16 1.03 Test area 4C CBC01 0.29 0.83 0.31 2.13 CBC02 0.16 0.47 0.17 1.12 CBC03 0.15 0.44 0.20 1.27 CBC04 0.19 0.51 0.24 1.58 CBC05 0.21 0.59 0.26 1.65 CBC06 0.15 0.42 0.23 1.51 CBC07 0.24 0.68 0.34 2.31 CBC08 0.22 0.55 0.33 2.29 CBC09 0.08 0.22 0.12 0.70 CBC10 0.24 0.62 0.32 2.04 CBC11 0.17 0.35 0.33 2.22 CBC12 0.20 0.44 0.26 1.65 CBC13 0.10 0.26 0.13 0.76 CBC14 0.14 0.37 0.17 1.16 CBC15 0.25 0.61 0.32 2.08 CBC16 0.19 0.45 0.19 1.24 CBC17 0.21 0.51 0.21 1.14 CBC18 0.15 0.33 0.17 0.81 CBC19 0.27 0.57 0.22 1.27 CBC20 0.20 0.53 0.19 1.29 CBC21 0.12 0.32 0.11 0.65 CBC22 0.19 0.48 0.18 1.07 CBC23 0.17 0.44 0.16 1.12 CBC24 0.18 0.47 0.15 0.98 CBC25 0.26 0.70 0.28 1.84 CBC26 0.14 0.29 0.15 0.68 CBC27 0.12 0.25 0.15 0.85 CBC28 0.25 0.69 0.25 1.72 CBC29 0.19 0.52 0.20 1.37 CBC30 0.11 0.23 0.19 0.76 CBC31 0.17 0.44 0.18 1.10 CBC32 0.15 0.31 0.22 1.01 CBC33 0.19 0.35 0.26 1.73 CBC34 0.15 0.27 0.20 1.07 CBC35 0.16 0.41 0.19 1.18 CBC36 0.17 0.41 0.22 1.49 CBC37 0.23 0.59 0.24 1.68 CBC38 0.18 0.36 0.18 1.21 School of Architecture, CUHK Page 395 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 5 Tsuen Wan summer Annual Test point VRw Vpw VRw Vpw Test area 5A TWA01 0.15 0.60 0.13 0.77 TWA02 0.18 0.74 0.18 1.05 TWA03 0.14 0.49 0.10 0.60 TWA04 0.18 0.80 0.18 1.15 TWA05 0.17 0.68 0.17 1.01 TWA06 0.20 0.74 0.16 0.99 TWA07 0.21 0.87 0.17 1.03 TWA08 0.21 0.83 0.18 1.08 TWA09 0.13 0.52 0.10 0.64 TWA10 0.16 0.63 0.14 0.84 TWA11 0.12 0.53 0.11 0.68 TWA12 0.20 0.73 0.15 0.78 TWA13 0.20 0.81 0.15 0.91 TWA14 0.12 0.52 0.10 0.63 TWA15 0.14 0.61 0.12 0.75 TWA16 0.15 0.66 0.14 0.90 TWA17 0.25 0.85 0.19 1.14 TWA18 0.16 0.72 0.16 1.03 TWA19 0.22 0.92 0.19 1.19 TWA20 0.21 0.82 0.16 0.93 TWA21 0.27 1.19 0.25 1.63 TWA22 0.19 0.83 0.17 1.12 TWA23 0.15 0.54 0.12 0.75 TWA24 0.17 0.71 0.17 1.09 TWA25 0.14 0.59 0.12 0.78 TWA26 0.24 1.00 0.22 1.38 Test area 5B TWB01 0.29 1.10 0.36 2.25 TWB02 0.30 1.35 0.32 2.15 TWB03 0.24 0.92 0.28 1.77 TWB04 0.22 0.93 0.26 1.66 TWB05 0.33 1.46 0.35 2.35 TWB06 0.26 1.08 0.32 2.14 TWB07 0.34 1.50 0.31 2.07 TWB08 0.18 0.75 0.16 1.02 TWB09 0.22 0.92 0.16 0.92 TWB10 0.24 0.99 0.29 1.71 TWB11 0.29 1.27 0.28 1.84 TWB12 0.20 0.87 0.19 1.24 TWB13 0.31 1.34 0.33 2.20 TWB14 0.29 1.20 0.26 1.69 TWB15 0.27 1.23 0.25 1.72 TWB16 0.23 0.95 0.27 1.77 TWB17 0.23 0.93 0.28 1.82 TWB18 0.15 0.64 0.14 0.89 TWB19 0.26 1.04 0.21 1.31 TWB20 0.27 1.16 0.24 1.53 TWB21 0.15 0.63 0.14 0.81 TWB22 0.17 0.75 0.14 0.88 TWB23 0.31 1.38 0.28 1.84 Test area 5C TWC01 0.13 0.58 0.14 0.87 School of Architecture, CUHK Page 396 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT TWC02 0.26 1.01 0.19 1.01 TWC03 0.22 0.78 0.15 0.85 TWC04 0.28 1.01 0.20 1.08 TWC05 0.17 0.67 0.13 0.81 TWC06 0.19 0.75 0.17 1.02 TWC07 0.15 0.61 0.12 0.71 TWC08 0.18 0.79 0.16 1.04 TWC09 0.19 0.76 0.14 0.78 TWC10 0.25 1.09 0.22 1.36 TWC11 0.21 0.73 0.17 1.02 TWC12 0.23 0.96 0.20 1.29 TWC13 0.22 0.75 0.17 0.95 TWC14 0.27 1.11 0.31 2.04 TWC15 0.22 0.95 0.20 1.29 TWC16 0.30 1.32 0.28 1.84 TWC17 0.31 1.31 0.29 1.94 TWC18 0.25 1.03 0.22 1.42 TWC19 0.15 0.57 0.13 0.70 TWC20 0.24 1.05 0.22 1.44 TWC21 0.23 0.89 0.19 1.17 TWC22 0.22 0.96 0.21 1.24 TWC23 0.25 1.07 0.22 1.36 TWC24 0.16 0.69 0.19 1.15 TWC25 0.24 1.03 0.25 1.66 TWC26 0.25 0.99 0.25 1.51 TWC27 0.34 1.47 0.30 1.88 TWC28 0.25 0.90 0.22 1.23 TWC29 0.25 1.12 0.28 1.84 TWC30 0.38 1.77 0.36 2.22 TWC31 0.27 1.12 0.23 1.44 TWC32 0.35 1.49 0.28 1.75 TWC33 0.29 1.27 0.30 2.02 TWC34 0.32 1.42 0.35 2.34 TWC35 0.27 1.11 0.26 1.65 TWC36 0.24 0.92 0.19 1.11 School of Architecture, CUHK Page 397 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 6 San Po Kong summer Annual Test point VRw Vpw VRw Vpw Test area 6A A01 0.09 0.73 0.12 1.17 A02 0.12 1.03 0.15 1.61 A03 0.16 1.31 0.17 1.73 A04 0.16 1.40 0.15 1.75 A05 0.16 1.23 0.13 1.34 A06 0.16 1.30 0.15 1.57 A07 0.20 1.74 0.17 1.87 A08 0.19 1.74 0.18 2.06 A09 0.15 1.26 0.17 1.86 A10 0.10 0.87 0.14 1.57 A11 0.13 1.00 0.16 1.94 A12 0.17 1.44 0.20 2.27 A13 0.16 1.24 0.16 1.70 A14 0.17 1.49 0.14 1.46 A15 0.17 1.28 0.18 2.06 A16 0.16 1.40 0.12 1.11 A17 0.16 1.43 0.16 1.92 A18 0.20 1.70 0.20 2.15 A19 0.12 0.91 0.10 1.09 A20 0.13 1.11 0.11 1.26 A21 0.09 0.78 0.11 1.32 A22 0.11 0.91 0.12 1.45 A23 0.11 0.88 0.08 0.78 A24 0.08 0.64 0.08 0.87 A25 0.15 1.30 0.12 1.35 A26 0.16 1.49 0.12 1.36 A27 0.19 1.74 0.13 1.23 A28 0.17 1.30 0.10 0.93 Test area 6B B01 0.13 1.06 0.13 1.47 B02 0.12 1.04 0.11 1.27 B03 0.10 0.86 0.08 0.95 B04 0.13 1.00 0.10 1.04 B05 0.10 0.86 0.08 0.87 B06 0.09 0.75 0.07 0.83 B07 0.13 1.20 0.13 1.55 B08 0.15 1.35 0.12 1.31 B09 0.18 1.57 0.16 1.75 B10 0.17 1.49 0.12 1.31 B11 0.17 1.46 0.14 1.62 B12 0.14 1.24 0.12 1.34 B13 0.13 1.14 0.11 1.30 B14 0.14 1.27 0.12 1.42 B15 0.09 0.85 0.08 0.99 B16 0.12 1.04 0.10 1.16 B17 0.14 1.22 0.10 1.11 B18 0.18 1.52 0.13 1.40 B19 0.21 1.79 0.18 1.95 B20 0.22 1.92 0.17 1.93 B21 0.16 1.44 0.14 1.56 B22 0.15 1.27 0.10 0.92 B23 0.19 1.58 0.14 1.57 B24 0.18 1.51 0.12 1.27 B25 0.14 1.14 0.11 1.13 B26 0.13 0.99 0.10 1.08 B27 0.15 1.29 0.11 1.22 B28 0.15 1.36 0.12 1.34 B29 0.14 1.23 0.12 1.35 School of Architecture, CUHK Page 398 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT B30 0.15 1.28 0.12 1.33 B31 0.22 1.81 0.16 1.71 B32 0.15 1.26 0.12 1.39 Test area 6C C01 0.09 0.74 0.10 1.10 C02 0.20 1.82 0.20 2.45 C03 0.22 2.07 0.21 2.46 C04 0.12 1.05 0.12 1.50 C05 0.12 1.07 0.12 1.49 C06 0.11 0.94 0.11 1.37 C07 0.18 1.57 0.20 2.40 C08 0.13 1.19 0.13 1.62 C09 0.17 1.51 0.19 2.09 C10 0.18 1.66 0.16 1.85 C11 0.13 1.10 0.15 1.63 C12 0.15 1.24 0.13 1.47 C13 0.09 0.77 0.08 0.86 C14 0.13 1.06 0.10 1.07 C15 0.17 1.45 0.17 1.95 C16 0.17 1.43 0.17 1.91 C17 0.16 1.32 0.17 1.91 C18 0.15 1.27 0.13 1.55 C19 0.11 0.97 0.08 0.97 C20 0.20 1.76 0.17 2.02 C21 0.24 2.21 0.19 2.11 C22 0.12 1.03 0.09 0.99 C23 0.17 1.52 0.12 1.24 C24 0.17 1.52 0.15 1.75 C25 0.12 1.11 0.10 1.17 C26 0.21 1.93 0.18 1.97 C27 0.29 2.54 0.26 2.98 C28 0.22 2.01 0.22 2.58 C29 0.24 2.10 0.18 1.91 C30 0.22 1.80 0.21 2.31 C31 0.19 1.52 0.12 1.16 C32 0.12 1.06 0.10 1.16 C33 0.19 1.69 0.16 1.87 C34 0.16 1.47 0.15 1.72 School of Architecture, CUHK Page 399 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 7 Tuen Mun summer Annual Test point VRw Vpw VRw Vpw Test area 7A N01 0.13 0.70 0.13 0.79 N02 0.14 0.66 0.15 0.90 N03 0.14 0.79 0.15 0.96 N04 0.13 0.68 0.13 0.81 N05 0.16 0.77 0.16 0.91 N06 0.14 0.76 0.14 0.85 N07 0.12 0.63 0.11 0.67 N08 0.14 0.71 0.13 0.84 N09 0.16 0.74 0.19 1.06 N10 0.14 0.74 0.13 0.80 N11 0.12 0.60 0.12 0.72 N12 0.16 0.81 0.14 0.88 N13 0.17 0.79 0.21 1.12 N14 0.21 1.05 0.21 1.23 N15 0.15 0.72 0.13 0.74 N16 0.14 0.74 0.14 0.82 N17 0.18 0.87 0.16 0.85 N18 0.16 0.84 0.19 1.07 N19 0.20 1.02 0.18 1.06 N20 0.15 0.82 0.15 0.95 N21 0.16 0.79 0.15 0.84 N22 0.20 0.97 0.17 0.95 N23 0.19 1.00 0.20 1.14 N24 0.16 0.77 0.14 0.83 N25 0.20 0.95 0.16 0.93 N26 0.16 0.79 0.14 0.81 N27 0.19 0.89 0.16 0.96 N28 0.30 1.43 0.25 1.35 N29 0.19 0.80 0.15 0.85 N30 0.22 1.00 0.17 0.99 N31 0.18 0.91 0.15 0.87 N32 0.24 1.07 0.16 0.88 Test area 7B S01 0.16 0.81 0.15 0.98 S02 0.09 0.47 0.11 0.67 S03 0.30 1.53 0.25 1.57 S04 0.16 0.82 0.17 1.08 S05 0.27 1.35 0.21 1.26 S06 0.17 0.91 0.18 1.09 S07 0.17 0.95 0.17 1.05 S08 0.21 0.97 0.19 1.14 S09 0.19 0.81 0.18 1.03 S10 0.19 0.93 0.21 1.21 S11 0.24 1.20 0.25 1.45 S12 0.15 0.75 0.16 1.02 S13 0.28 1.35 0.26 1.59 S14 0.13 0.70 0.14 0.91 S15 0.25 1.26 0.24 1.56 S16 0.21 1.05 0.19 1.21 S17 0.25 1.24 0.26 1.67 S18 0.15 0.74 0.20 1.12 S19 0.18 0.95 0.20 1.31 S20 0.12 0.63 0.15 0.96 S21 0.20 0.98 0.18 1.11 S22 0.15 0.77 0.15 0.96 S23 0.20 1.11 0.22 1.46 S24 0.21 1.07 0.19 1.21 S25 0.16 0.78 0.14 0.82 School of Architecture, CUHK Page 400 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT S26 0.21 1.07 0.21 1.27 S27 0.18 0.88 0.18 1.06 S28 0.19 0.83 0.15 0.76 S29 0.19 0.73 0.14 0.73 S30 0.23 1.20 0.19 1.16 Test area 7C O01 0.16 0.74 0.15 0.82 O02 0.17 0.81 0.18 1.06 O03 0.22 1.01 0.15 0.66 O04 0.18 0.93 0.18 1.15 O05 0.16 0.87 0.16 1.02 O06 0.19 1.01 0.20 1.27 O07 0.26 1.27 0.24 1.22 O08 0.22 1.18 0.24 1.54 O09 0.20 1.08 0.21 1.28 O10 0.16 0.84 0.15 0.94 O11 0.17 0.93 0.19 1.21 O12 0.13 0.68 0.16 0.90 O13 0.11 0.54 0.11 0.67 O14 0.20 0.96 0.22 1.09 O15 0.14 0.74 0.13 0.78 O16 0.15 0.78 0.19 1.11 O17 0.30 1.50 0.25 1.51 O18 0.22 1.05 0.13 0.53 O19 0.28 1.50 0.28 1.77 O20 0.28 1.47 0.26 1.45 O21 0.26 1.39 0.29 1.85 O22 0.12 0.67 0.13 0.84 O23 0.16 0.81 0.15 0.86 O24 0.19 0.97 0.18 1.11 O25 0.20 1.00 0.18 1.08 O26 0.21 1.08 0.20 1.20 O27 0.23 1.11 0.22 1.27 O28 0.24 1.24 0.23 1.34 O29 0.21 0.98 0.17 0.93 O30 0.21 1.07 0.23 1.42 O31 0.25 1.31 0.22 1.33 O32 0.29 1.47 0.27 1.55 O33 0.17 0.80 0.14 0.79 School of Architecture, CUHK Page 401 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 8 Sha Tin summer Annual Test point VRw Vpw VRw Vpw Test area A01 0.18 1.20 0.22 1.79 8A A02 0.18 1.34 0.19 1.69 A03 0.16 1.12 0.24 2.04 A04 0.16 1.28 0.20 1.80 A05 0.13 0.95 0.18 1.57 A06 0.19 1.09 0.27 2.23 A07 0.15 1.12 0.17 1.37 A08 0.17 1.18 0.19 1.39 A09 0.17 1.22 0.20 1.72 A10 0.13 1.04 0.15 1.31 A11 0.18 1.34 0.25 2.14 A12 0.20 1.35 0.25 2.10 A13 0.16 1.15 0.18 1.63 A14 0.16 1.08 0.21 1.78 A15 0.15 1.12 0.21 1.89 A16 0.12 0.91 0.13 1.20 A17 0.20 1.53 0.26 2.28 A18 0.26 1.94 0.28 2.41 A19 0.21 1.48 0.25 2.04 A20 0.17 1.20 0.24 2.03 A21 0.19 1.21 0.26 2.30 A22 0.17 1.21 0.22 1.69 A23 0.18 1.27 0.17 1.31 A24 0.22 1.25 0.29 1.97 A25 0.13 0.94 0.18 1.51 A26 0.20 1.48 0.22 1.69 A27 0.16 1.03 0.23 1.87 A28 0.14 1.08 0.14 1.05 A29 0.16 1.21 0.19 1.62 A30 0.19 1.43 0.23 2.03 A31 0.12 0.91 0.12 1.08 A32 0.19 1.38 0.17 1.46 A33 0.18 1.43 0.17 1.52 A34 0.17 1.33 0.16 1.37 A35 0.16 1.29 0.16 1.49 Test area B01 0.15 1.22 0.14 1.27 8B B02 0.17 1.34 0.19 1.71 B03 0.18 1.20 0.19 1.54 B04 0.20 1.56 0.19 1.54 B05 0.20 1.42 0.18 1.57 B06 0.22 1.73 0.22 1.86 B07 0.19 1.56 0.16 1.41 B08 0.18 1.17 0.20 1.55 B09 0.17 1.33 0.15 1.26 B10 0.19 1.38 0.19 1.59 B11 0.23 1.78 0.24 2.13 B12 0.19 1.44 0.20 1.69 B13 0.20 1.52 0.16 1.32 B14 0.23 1.88 0.21 1.85 B15 0.23 1.82 0.23 1.99 School of Architecture, CUHK Page 402 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT B16 0.21 1.63 0.22 1.74 B17 0.23 1.75 0.22 1.85 B18 0.21 1.67 0.20 1.80 B19 0.19 1.43 0.21 1.77 B20 0.24 1.87 0.23 1.83 B21 0.24 1.91 0.22 1.63 B22 0.21 1.66 0.21 1.72 B23 0.21 1.67 0.21 1.84 B24 0.24 1.89 0.24 2.05 B25 0.19 1.39 0.19 1.48 B26 0.14 1.04 0.14 1.07 B27 0.17 1.39 0.15 1.21 B28 0.19 1.48 0.19 1.62 Test area C01 0.20 1.31 0.26 2.08 8C C02 0.18 1.00 0.27 2.24 C03 0.21 1.30 0.27 2.13 C04 0.21 1.56 0.26 2.30 C05 0.20 1.31 0.26 2.11 C06 0.18 1.38 0.23 2.08 C07 0.19 1.08 0.27 2.22 C08 0.21 1.17 0.29 2.27 C09 0.22 1.56 0.27 2.36 C10 0.11 0.72 0.14 1.04 C11 0.14 0.93 0.21 1.71 C12 0.18 1.24 0.27 2.30 C13 0.15 0.91 0.23 1.99 C14 0.21 1.29 0.29 2.49 C15 0.18 0.97 0.24 1.95 C16 0.17 1.12 0.19 1.70 C17 0.20 1.33 0.21 1.76 C18 0.23 1.45 0.25 2.02 C19 0.18 1.22 0.21 1.79 C20 0.23 1.54 0.28 2.16 C21 0.17 1.12 0.21 1.65 C22 0.18 1.37 0.19 1.69 C23 0.16 1.00 0.20 1.59 C24 0.16 0.99 0.18 1.40 C25 0.24 1.90 0.27 2.37 C26 0.15 1.22 0.14 1.23 C27 0.22 1.78 0.20 1.71 C28 0.16 1.33 0.16 1.39 C29 0.19 1.45 0.17 1.48 C30 0.15 1.17 0.16 1.51 C31 0.17 1.29 0.14 1.19 School of Architecture, CUHK Page 403 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 9 Tseung Kwan O summer Annual Test point VRw Vpw VRw Vpw Test area 9A A01 0.16 0.88 0.17 1.01 A02 0.18 0.99 0.20 1.14 A03 0.20 1.01 0.26 1.64 A04 0.16 0.80 0.20 1.15 A05 0.13 0.64 0.16 0.93 A06 0.18 0.99 0.17 1.07 A07 0.14 0.80 0.15 0.95 A08 0.12 0.61 0.14 0.91 A09 0.18 0.91 0.15 0.88 A10 0.14 0.69 0.11 0.62 A11 0.16 0.91 0.17 1.08 A12 0.18 1.01 0.16 0.99 A13 0.21 1.15 0.19 1.24 A14 0.16 0.89 0.15 0.87 A15 0.13 0.68 0.13 0.85 A16 0.16 0.91 0.18 1.06 A17 0.16 0.89 0.18 0.98 A18 0.15 0.84 0.15 0.87 A19 0.12 0.64 0.11 0.72 A20 0.17 0.85 0.17 0.98 A21 0.13 0.70 0.12 0.75 A22 0.17 0.87 0.18 1.10 A23 0.18 0.95 0.19 1.18 Test area 9B B01 0.20 1.11 0.22 1.38 B02 0.12 0.68 0.13 0.85 B03 0.10 0.52 0.09 0.55 B04 0.20 0.98 0.25 1.47 B05 0.19 0.98 0.23 1.37 B06 0.14 0.77 0.15 0.93 B07 0.21 1.13 0.22 1.33 B08 0.16 0.82 0.17 1.05 B09 0.21 1.09 0.23 1.39 B10 0.20 1.07 0.21 1.28 B11 0.18 0.99 0.18 1.08 B12 0.20 1.07 0.18 1.07 B13 0.20 1.09 0.18 1.04 B14 0.18 0.97 0.21 1.28 B15 0.17 0.88 0.20 1.25 B16 0.16 0.91 0.16 1.02 B17 0.22 1.22 0.21 1.35 B18 0.18 0.98 0.17 1.07 B19 0.18 0.92 0.21 1.28 B20 0.15 0.86 0.17 1.05 Test area 9C C01 0.16 0.92 0.15 0.91 C02 0.18 0.95 0.15 0.84 C03 0.19 1.00 0.19 1.12 C04 0.22 1.20 0.22 1.33 C05 0.19 0.94 0.17 1.00 C06 0.15 0.79 0.13 0.77 C07 0.21 1.12 0.18 1.08 School of Architecture, CUHK Page 404 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT C08 0.17 0.98 0.17 1.11 C09 0.18 0.95 0.18 1.02 C10 0.19 1.04 0.20 1.24 C11 0.21 1.12 0.21 1.28 C12 0.24 1.26 0.19 1.05 C13 0.26 1.35 0.22 1.28 C14 0.25 1.39 0.26 1.66 C15 0.19 1.09 0.20 1.24 C16 0.24 1.24 0.23 1.27 C17 0.25 1.34 0.21 1.18 Test area 1C D01 0.21 1.15 0.22 1.38 D02 0.21 1.09 0.26 1.52 D03 0.24 1.34 0.25 1.55 D04 0.22 1.05 0.28 1.72 D05 0.24 1.22 0.30 1.77 D06 0.22 1.23 0.26 1.58 D07 0.23 1.19 0.28 1.58 D08 0.19 0.66 0.28 1.39 D09 0.19 0.86 0.25 1.31 D10 0.21 1.21 0.19 1.18 D11 0.18 0.87 0.14 0.71 D12 0.19 0.98 0.16 0.95 D13 0.21 1.14 0.18 1.07 D14 0.16 0.86 0.17 1.06 D15 0.15 0.80 0.16 1.05 O01 0.20 1.13 0.22 1.43 O02 0.16 0.86 0.18 1.08 O03 0.16 0.85 0.18 1.12 O04 0.25 1.18 0.30 1.76 O05 0.23 1.15 0.28 1.65 O06 0.21 0.77 0.27 1.40 O07 0.17 0.88 0.21 1.34 O08 0.16 0.77 0.22 1.23 O09 0.20 0.99 0.26 1.53 O10 0.22 1.03 0.27 1.50 O11 0.20 0.92 0.25 1.41 O12 0.21 1.02 0.26 1.44 O13 0.18 0.96 0.19 1.17 O14 0.22 1.24 0.20 1.21 O15 0.24 1.37 0.23 1.38 O16 0.23 1.31 0.22 1.38 O17 0.15 0.85 0.14 0.76 O18 0.25 1.45 0.22 1.42 O19 0.28 1.56 0.27 1.62 O20 0.25 1.40 0.22 1.30 O21 0.20 1.10 0.18 1.05 O22 0.23 1.29 0.22 1.29 O23 0.17 0.89 0.16 0.86 School of Architecture, CUHK Page 405 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Test area 10 Wong Chuk Hang summer Annual Test point VRw Vpw VRw Vpw Test area 10A A01 0.23 1.08 0.22 1.29 A02 0.21 1.15 0.19 1.27 A03 0.11 0.62 0.11 0.71 A04 0.13 0.68 0.16 1.08 A05 0.14 0.66 0.18 1.24 A06 0.19 1.09 0.22 1.53 A07 0.16 0.79 0.22 1.49 A08 0.19 0.89 0.18 1.14 A09 0.2 1.07 0.18 1.22 A10 0.23 1.28 0.21 1.37 A11 0.25 1.23 0.18 1.07 A12 0.28 1.61 0.22 1.46 A13 0.12 0.64 0.15 0.96 A14 0.29 1.72 0.26 1.69 A15 0.15 0.72 0.13 0.84 A16 0.21 1.21 0.19 1.16 A17 0.1 0.52 0.1 0.65 A18 0.21 1.12 0.18 1.2 A19 0.19 0.88 0.2 1.25 A20 0.19 1.11 0.17 1.15 A21 0.3 1.76 0.25 1.66 A22 0.23 1.33 0.2 1.25 A23 0.25 1.35 0.24 1.47 A24 0.18 1.06 0.18 1.25 A25 0.18 0.96 0.16 0.99 Test area 10B B01 0.26 1.49 0.26 1.69 B02 0.19 0.98 0.18 1.15 B03 0.18 1.01 0.17 1.12 B04 0.24 1.39 0.21 1.39 B05 0.25 1.48 0.24 1.55 B06 0.26 1.53 0.25 1.62 B07 0.27 1.59 0.22 1.5 B08 0.32 1.84 0.26 1.76 B09 0.27 1.54 0.25 1.65 B10 0.29 1.66 0.28 1.89 B11 0.33 1.89 0.33 2.16 B12 0.28 1.65 0.27 1.79 B13 0.19 1.04 0.2 1.3 B14 0.21 1.14 0.2 1.35 B15 0.23 1.26 0.22 1.44 B16 0.24 1.41 0.23 1.56 B17 0.24 1.27 0.24 1.5 B18 0.15 0.84 0.14 0.91 B19 0.26 1.45 0.25 1.62 B20 0.14 0.85 0.13 0.88 B21 0.21 1.17 0.2 1.3 B22 0.16 0.93 0.16 1.03 B23 0.18 1.01 0.17 1.18 B24 0.24 1.23 0.25 1.65 B25 0.14 0.71 0.18 1.11 School of Architecture, CUHK Page 406 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT B26 0.31 1.76 0.27 1.78 B27 0.18 1.05 0.18 1.2 B28 0.33 1.91 0.31 2.03 B29 0.24 1.34 0.23 1.5 B30 0.23 1.22 0.24 1.48 Test area 10C C01 0.24 1.34 0.23 1.48 C02 0.22 1.26 0.21 1.4 C03 0.22 1.15 0.2 1.37 C04 0.16 0.82 0.15 0.99 C05 0.19 0.89 0.14 0.84 C06 0.21 1.1 0.18 1.18 C07 0.36 2.03 0.29 1.89 C08 0.22 1.24 0.17 1.09 C09 0.25 1.42 0.24 1.69 C10 0.23 1.22 0.23 1.49 C11 0.24 1.37 0.22 1.46 C12 0.22 1.29 0.22 1.43 C13 0.22 1.22 0.23 1.46 C14 0.27 1.47 0.25 1.74 C15 0.18 0.91 0.22 1.34 C16 0.25 1.43 0.27 1.65 C17 0.23 1.3 0.22 1.45 C18 0.2 1.06 0.16 0.99 C19 0.19 0.99 0.25 0.98 C20 0.22 1.2 0.19 1.29 C21 0.21 1.24 0.17 1.13 C22 0.32 1.73 0.27 1.67 C23 0.25 1.42 0.2 1.31 C24 0.23 1.23 0.24 1.5 C25 0.2 1.1 0.18 1.17 C26 0.27 1.52 0.26 1.68 C27 0.17 1 0.16 1.05 C28 0.25 1.37 0.22 1.38 C29 0.29 1.68 0.23 1.56 C30 0.29 1.66 0.23 1.52 C31 0.32 1.83 0.29 1.9 C32 0.32 1.82 0.26 1.71 School of Architecture, CUHK Page 407 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 4 : THE SITE WIND AVAILABILITY VS THE SITE MEAN WIND SPEED Based on data above, it is noted that, on the whole, there is no statistical correlation between the site wind availability (Vs) and the site mean wind (Vp) of the 20 study areas annually and in the summer months. annual summer annual summer Vs Vs A B A B site mean wind apeed site mean wind apeed TST 4.51 3.6 1.72 1.64 1.23 1.54 MK 4.43 3.69 1 1.15 0.85 0.85 CWB 3.64 2.84 1.53 1.33 1.24 1.27 SW 3.4 2.48 0.82 1.15 0.84 0.96 TW 3.82 3.26 1.22 1.47 1.06 1.32 SPK 3.08 2.95 1.53 1.33 1.24 1.27 TM 3.58 3.06 0.82 1.15 0.84 0.96 TKO 3.78 3.16 1 1.15 0.85 0.95 ShaTin 4.3 3.32 1.72 1.64 1.23 1.54 WCH 3.67 3.06 1.22 1.47 1.06 1.32 mean 3.82 3.14 sd 0.46 0.36 median 3.725 3.11 max 4.51 3.69 min 3.08 2.48 2 A annual B annual 1.8 A summer B summer 1.6 1.4 1.2 site mean site (summer) 1 0.8 0.6 2 2.5 3 3.5 4 4.5 5 summer mean 50% exceedance at 150mPD School of Architecture, CUHK Page 408 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 5 : ANALYSIS OF WIND SPEED DISTRIBUTION Tick means that the test site satisfies Condition A when the threshold value is applied. For example, if all (100%) of the test points need to satisfy the 1 m/s threshold value, then only 1 site (ST-8b) will comply. The “cliff” occurs at 80% and 95% respectively for 1 m/s and 0.6 m/s. The 60% and 50% columns are there for illustration only. We do not recommend them to be considered. School of Architecture, CUHK Page 409 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART IV: REFINEMENT OF AIR VENTILATION ASSESSMENT SYSTEM School of Architecture, CUHK Page 410 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART IV(A) INTRODUCTION AND REVIEW PART IV(A)-1 CURRENT AVA SYSTEM (AVAS) The current AVAS has identified an AVA methodology based on performance-based ―option comparison and improvement approach‖ and without quantitative yardsticks. It mainly focuses on improvement of scheme options, as wind standards have yet to be established. Given the limited urban climatic knowledge, technology and experiences at the time, the approach of pioneering and encouraging, rather than regulating, have been adopted for implementating the AVAS. The Government has taken the initiative to conduct AVA in improving overall design. The current AVAS is defined by the then HPLB and ETWB‘s Technical Circular and Technical Guide (Part IV – Appendix 1) on AVA and the relevant HKPSG Chapter 11. The current AVAS is limited in its effects due to the following reasons: - • Lack of quantitative data for existing pedestrian level wind conditions to analyse the performance, problem and issue in greater detail • Lack of a holistic understanding to aid planning and design strategically • Lack of research to develop quantitative yardsticks for wind performance • Lack of a consistent set of site wind availability data for AVA The UCM Study is tasked to bridge some of these information gaps with a view to providing a more scientific and objective basis for identifying climatically valuable and sensitive areas and assessing the impacts of major developments and planning proposals on the local wind environment. The UCM Study has produced the following technical inputs for the refined AVAS: • Wind tunnel benchmarking tests had been conducted to understand the exisiting pedestrian wind conditions of the urban areas in Hong Kong. • The Urban Climatic Planning Recommendation Map has been produced to aid strategic and district planning. On top of the annual average considerations, it is established that summer condition should be incorporated in AVA, as the summer (June – August) remains the most critical season for Hong Kong in urban climatic terms. • The Wind Performance Criterion has been established in consideration of the urban climatic considerations and thermal comfort. • It is recommended that site wind availability be provided by the PlanD for ensuring consistent wind data inputs for AVAs. School of Architecture, CUHK Page 411 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Taking into account the relevant findings of the UCM Study and the expert review of the implementation of the current AVAs, the Study has recommended the refinements to the AVAS, including revision to the AVA Technical Circular and Technical Guide (Part IV(B)), and a new HKPSG chapter (Part IV(C)). PART IV(A)-2 AN EXPERT REVIEW OF AVA STUDIES COMPLETED UNDER THE CURRENT AVAS A number of projects had gone through the current AVAS including expert evaluations, initial studies and detailed studies. An overall analysis has been conducted on the AVA register (as at end of July 2010) (see Part IV-Appendix 2) for consideration. It was found that AVA has been applied on both public and private sector developments with problem areas identified and improvement measures suggested. Expertise and experience in conducting AVAs are gradually maturing in Hong Kong, and AVAS has proven to be useful in guiding project proponents towards a better design thus attaining better urban air ventilation performance in general. Hence, it is considered opportune to extend the scope of application of the AVAS to include private sector projects. In the current AVAS, AVA is a design improvement tool and there is no quantitative yardstick; which is useful in its own right. However, there could be disputes on the acceptability of designs that have taken into account other design factors and forgone the maximum air ventilation performance, and whether the resultant air ventilation performance is still sufficient. As such, we need a quantitative benchmark as a yardstick. In-depth expert review has also been conducted on selected projects (listed below). Lessons learnt have been summarised in subsequent sections. Expert Evaluation Ho Man Tin Wong Nai Chung Tsim Sha Tsui Tsz Wan Shan, Diamond Hill and San Po Kong Yuen Long Shau Kei Wan Quarry Bay Computation Fluid Dynamics A/ST/625 Tai Wai Station AVA studies ESF King George V School AVA studies Taikoo Place AVA studies Wind Tunnel Test North Point Area (district-level study) New Central Harbourfront (district-level study) School of Architecture, CUHK Page 412 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Ex-North Point Estate (site-level study) Oil Street (site-level study) Tamar (site-level study) 2.1 Lessons Learnt from Expert Review of Expert Evaluation AVA Studies The following summarises the important lessons learnt from the review of AVA expert evaluations: Use of Expert Evaluation On the whole, all the Expert Evaluation reports follow a similar procedure and methodology. Various experts have come to a similar AVA understanding of breezeway, air path, setback, non-building area, building height differential, and podium coverage etc. This largely coincides with the Urban Climatic Map understanding of building volume, ground coverage, proximity to openness and topography. Summer Condition Summer as well as annual wind conditions are assessed. There is a consensus that urban air ventilation is most important in the summer months in terms of human outdoor thermal comfort in Hong Kong. Site Wind Availability Consultants currently use different sources of wind information, including computer simulated wind data, Hong Kong Observatory data, and wind tunnel test data, as and when available, for their assessments. It is useful for the PlanD to consider a unified set of data for the purpose of improving consistency and accuracy. The current site wind availability (V Infinity) data at about 596m above terrain level on PlanD‘s website (which was produced by EPD using MM5 model) may not have the necessary resolution of wind information needed for AVA. Urban Climatology The findings of the Urban Climatic Map can greatly assist the expert evaluation process by providing information on prevailing wind directions, urban morphology, thermal load/ dynamic potential, greenery, and topographical understanding. Experts undertaking AVA by expert evaluation for OZP review can refer to the macro level urban climatic understanding of the Urban Climatic Planning Recommendation Map. 2.2 Lessons learnt from Expert Review of AVA Initial Studies The following summarise the important lessons learnt from the review of AVA Initial Studies by CFD: School of Architecture, CUHK Page 413 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Need for Area and Point Assessment The use of SVR and LVR can represent the general picture of the air ventilation performance as a whole. However, both SVR and LVR have a drawback in that they would average out the results. Methods like area analysis or point by point analysis are needed to identify weak wind issues for the purpose of design optimisation. It is also useful for wind engineers to include tabulated VRi (directional velocity ratio) in addition to VRw (weighted velocity ratio) of test points. Summer Condition Currently, only annual wind VRs need to be reported. It is useful for the refined AVAS to include a requirement to report the summer VRs which are important for human outdoor thermal comfort. Technical Issues There seems to be 2 different approaches to account for the surrounding topography – some incorporate it into their models, whereas others have ignored it. This is problematic especially when the computer simulated site wind availability on PlanD‘s website is used. It is useful for PlanD to consider providing a standardised set of site wind availability data for consistent application. Different turbulence models are adopted in different CFD analyses. It is a common understanding that all turbulence models have their own limitations and there are many required parameters to be inserted to the turbulence models. As such, the accuracy of the CFD models cannot be guaranteed unless with careful quality control. It is also important to follow established CFD guidelines. Documentation For better referencing and quality assurance, it is useful for the report to include full documentation of the settings so that the quality of the simulated results can be evaluated. It is useful to follow best practices. Results of any pre-tests and sensitivity tests should be included. It is useful for the report to contain an appendix documenting the validation tests, if any, that have been conducted against known and robust field or experimental data, with the software, the turbulence model and the various settings used appropriately stated. This applies to studies that make use of site wind availability data from other studies. In this case, it is useful to reproduce the key information for reference. It is suggested that the documentation should cover the key parameters as identified in the COST14 Action Report, School of Architecture, CUHK Page 414 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT VDI 3783 Part 9, and the AIJ guidebook, including the following items: (Note: The list is not exhaustive, please refer to the text of the guidelines). • Choice of target variables • Choice of approximate equations describing the physics of the flow • Choice of geometrical representation of the obstacles • Choice of computational domain • Choice of boundary conditions • Choice of initial conditions • Choice of computational grid • Choice of time step size • Choice of numerical approximations • Choice of iterative convergence criteria 2.3 Lessons learnt from Expert Review of AVA Detailed Studies The following summarises the important lessons learnt from the review of AVA Detailed Studies: Need for Area and Point Assessment Similar to the observations identified in Section 2.2. Site Wind Availability - Resolution Techniques have been proposed and implemented in wind tunnel studies to better approximate the wind direction shifts at near urban canopy levels. It is useful for the PlanD to consider to establish a standardised set of site wind availability data for consistent application, improving accurancy and saving resources. Summer Condition Similar to the observations identified in Section 2.2. Documentation For better referencing and quality assurance, it is useful for the report to include full documentation of the settings so that the quality of the experimental results can be independently evaluated. This applies to assessments that make use of data from other studies; in which case, it would be useful to reproduce the key information. It is suggested that the following be included in the documentation: The wind profile, turbulence intensity profile and the power density spectrum must be included. In addition, the matching according to the model scale, the eddy sizes and longitudinal, lateral and vertical wind direction fluctuations may also be included to improve the scientific validity of the tests. Furthermore, the wind speed used for the wind tunnel model test should be stated. If it is pre-tested for Reynolds Number independence before the actual test, and that similarity of flow has been ensured, then School of Architecture, CUHK Page 415 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT this should be documented. The equipment used for the measurement and the results of their pre-test calibration, if any, should also be mentioned. Technical Issues - Surrounding Area Occasionally, using 2H for the surrounding area may not be enough. It may be useful to reproduce the upstream roughness for street openings at the edge of the model. This could avoid the possibly unrealistic parallel flow into the streets that might give optimistic results. Wind engineers must assess the condition carefully and expertly, and add additional building blocks beyond the 2H surrounding area that can represent the urban roughness in a more realistic manner. If in doubt, sensitivity tests may be carried out to ensure accuracy of results. The combined use of CFD and Wind Tunnel Some consultants utilise initial AVA studies based on CFD to identify focus areas for more in-depth analysis by detailed studies. This is a recommended strategy. 2.4 Refinements Suggested After reviewing the AVAs carried out by expert evaluation, initial study and detailed study, related recommendations have been drawn up as follows to improve the AVA System accordingly. Site Wind Availability (Vs) To ensure the accuracy and consistency of the various types of AVA for planning purpose, PlanD is strongly recommended to provide and make public a standardised set of site wind availability data. To accommodate for Hong Kong‘s complex local topography and the land and sea breeze phenomena, it is suggested that computer simulation method can be used to provide a fine resolution site wind availability data from a low level up to 500m covering the whole of Hong Kong. Since AVA is about pedestrian level wind and wind directions at the lower levels are of greater interest to planners, it is suggested that the wind rose at a height just over the urban canopy layer (UCL) height level should be appropriate. For AVA initial and detailed studies, this can then be further extrapolated using the appropriate Power or Log law, or by referring to the model simulated wind profiles as mentioned in the paragraph above, when calculating VR using V500. The area average building height of Hong Kong has been studied, it is found to be in the range of 60 to 90m above ground level. According to literature, it is suggested that UCL = 1.2 * building height be used, thus the UCL is about 75m to 110m in Hong Kong. School of Architecture, CUHK Page 416 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT The Vs is to be positioned on top of the roughness sub-layer39 of the urban environment. Therefore, it is suggested that Vs be set at 2 or 2.5 times UCL, or 200m to 300m above ground (Oke, 1987, 1997; Grimmond and Oke, 1999). Summer Condition In addition to annual VRs, Summer VRs are recommended to be included in the refined AVAS. This will allow better consideration of wind for urban thermal comfort in the hot and humid summer months of Hong Kong. Area and Point Analysis In addition to SVR and LVR, area and point evaluation of VRs are recommended to be included. More detailed analysis is to be made available for design decision making. Sometimes, VRi may also be needed to examine the directional impact of a development. As every location varies, planners are recommended to work closely with consultants and wind engineers to see how the data can be most appropriately understood. Technical Issues Various technical issues are identified for different types of AVA. In Expert Evaluation for district studies, analysis of urban climatology issues will be relevant and useful. For AVA using CFD, the modelling methodology and input parameters will be essential for accuracy. For wind tunnels, the extent of the surrounding area may sometimes need to be extended beyond 2H to allow replication of the upstream roughness. These technical matters have to be properly addressed in the AVAS. Full Documentation For better referencing and quality assurance, the model settings, methodology, approach, and equipment used, etc., have to be fully documented for independent evaluation. This applies to both CFD and wind tunnel. Possible Design Improvements Based on air ventilation design principles and/or analysis of AVA results, alternative design can be drawn up for development proposals. It is useful and important to prepare and evaluate alternative designs, in order to understand and demonstrate their effects and improve the overall design. 39 Roughness Sub-layer is the layer in contact with the terrestrial surface in which the flow fields are influenced by the characteristics of the urban strcutures. School of Architecture, CUHK Page 417 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART IV(A)-3 KEY FINDINGS RELEVANT TO THE REFINEMENT OF AVAS The key findings of the study relevant to the refinement of the AVAS - Technical Circular No.1/06 on AVA which jointly issued by the ex-Housing, Planning and Lands Bureau (HPLB) and ex-Environment, Transport and Works Bureau (ETWB) in July 2006 are explained below. Wind Performance Criterion Balancing the desirable minimium wind requirement and practical considerations of the existing built environment, a Wind Performance Criterion comprising the Wind Performance Requirement and the Alternative (Prescriptive) Approach with an exemption clause are proposed. The Wind Performance Criterion should be incorporated in the AVAS to provide a quantitative yardstick to assess the acceptability of air ventilation performance of development projects. Summer thermal comfort According to the findings of the Urban Climatic Maps of Hong Kong, which took into account the users thermal comfort survey, benchmarking studies and the findings of the Wind Performance Criterion study, summer wind condition is shown to be more critical to the urban climatic environment of Hong Kong than other times of the year. As such, it would be useful to include the summer air ventilation analysis as a study requirement in the refinement of AVAS. Wind Velocity at Site Wind Availability Level (Vs) [formerly Wind Velocity at Infinity - V(infinity) at 500m] In view of Hong Kong‘s complicated topography and in reference to the wind information layer of the Hong Kong Urban Climatic Maps, instead of using V(infinity), which is taken to be at a relatively high altitude of about 500m, it is considered more accurate to adopt a wind rose at a height level of 300m or lower (thus nearer to the urban canopy level). This will improve the consistency and accuracy for AVA as the effects of the surrounding topography on the wind flows can be better accounted for. It would be necessary for PlanD to create a set of reasonable site wind availability (Vs) data nearer the urban canopy level to facilitate this AVA. Sea breezes – implication on site wind availability It is noted that sea breeze is an important consideration especially in the western territory of Hong Kong and on both sides of Victoria Harbour. This may not be fully accounted for if only HKO Waglan Island data is used as inputs for assessing site wind availability. Again, it School of Architecture, CUHK Page 418 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT would be necessary for PlanD to create a set of reasonable site wind availability (Vs) data that takes into account the sea breeze for AVA. Sensitive locations The intra-urban climatic condition is highly location dependent. It is useful to focus the wind (air ventilation) consideration on important locations, for example, building entrances, open spaces and frequently patronised streets where people congregate and pass through. Stagnancy in these important locations will be of greater concern. Hence, it is important to define the locations of test points with great care in order to cover relevant/appropriate locations and assess adequately the air ventilation impact of a proposed development on the sensitive receivers. It is also useful to have more test points closer to the boundary of the project site, to better evaluate the impact of the project on urban air ventilation of its surroundings. PART IV(A)-4 INTERNATIONAL BEST PRACTICE – USEFUL AND RELEVANT CODES AND STANDARDS (1) Code of practice for conducting AVA using wind tunnel The two documents below remains the more authoritative references for engineers conducting AVA using wind tunnel. Their continued use is recommended. (a) Manuals and Reports on Engineering Practice No. 67 : Wind Tunnel Studies of Buildings and Structures, Virginia 1999 issued by American Society of Civil Engineers. (b) Wind Engineering Studies of Buildings, Quality Assurance Manual on Environment Wind Studies AWES-QAM-1-2001 issued by Australasian Wind Engineering Society. (2) Code of practice for conducting AVA using CFD The 2006 Technical Circular has included the following paragraph on the use of CFD: “Computational Fluid Dynamics (CFD) may be used with caution, it is more likely admissible for the Initial Studies. There is no internationally recognised guideline or standard for using CFD in outdoor urban scale studies. The onus is on the assessor to demonstrate that the tool used is “fit for the purpose.” Today it is possible for consultants to refer to the following 4 useful texts when configuring the files and settings for CFD model simulation. School of Architecture, CUHK Page 419 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (a) Architectural Institute of Japan (2007), AIJ Guidebook for Practical Applications of CFD to Pedestrian Wind Environment around Buildings. [ISBN 978-4-8189-2665- 3] [Also read Tominaga Y et. a. (2006) ditto, Journal of Wind Engineering and Industrial Aerodynamics, Volume 96, Issues 10-11, October-November 2008, Pages 1749-1761.] (b) Franke J et. al. (2004), Recommendations on the Use of CFD on Predicting Pedestrian Wind Environment <17.05.2004 version 1.0>, in Proceedings of the International Conference on Urban Wind Engineering and Building Aerodynamics – Cost Action C14, Impact of Wind and Storm on City Life and Built Environment, edited by J P A J van Beeck, von Karman Institute for Fluid Dynamics, May 2004. (c) Michael Schatzmann, Helge Olesen and Jörg Franke, COST Action 732 – Quality Assurance and Improvement of Microscale Meteorological Models, Feb 2010. ISBN: 3-00-018312-4. (d) VDI, (2005) Environmental Meteorology - Prognostic Microscale Wind field Models - Evaluation for Flow around Buildings and Obstacles, VDI/DINHandbuch Reinhaltung der Luft. Beuth, Berlin, 53 pp. VDI 3783 part 9. Due to the heigtening of computational power, CFD has advanced rapidly to the extent that they may now be feasible to be used for outdoor wind environment simulation studies, but great care is still needed as the level of accuracy of using CFD is in general not comparable to wind tunnel tests and is more difficult to ascertain. Thus, it is suggested that CFD utilising the appropriate RANS, DES or LES models, when used properly, be continue to be allowed for AVA Initial Studies giving ―patterns‖ and rough quantitative estimates of the wind environment of the assessment areas. PART IV(B) THE REFINED AVAS AND RATIONALE The AVAS is defined by Technical Circular No. 1/06 on Air Ventilation Assessment and the relevant Hong Kong Panning Standards and Guidelines (HKPSG) Chapter. As such, the Technical Circular and HKPSG are reviewed for refining the AVAS. Scope of AVA AVA is required for projects meeting the criteria listed in the Technical Circular No. 1/06. Based on past experiences, such an arrangement can ensure that air ventilation would be considered in those cases required to conduct AVA at their early planning and design stages. Therefore, the list of categories of projects requiring AVA as set down in the Technical Circular should be kept. School of Architecture, CUHK Page 420 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT In order to clarify the scope and requirement of AVA and impose adequate control on elongated inland lots, the following changes are recommended:- (a) Before there is a definitive standard for AVA, the government has been taking the lead in carrying out AVAs for all major development proposals in the past few years. The private sector has also been proactively undertaking AVA to improve their scheme design. Expertise and experience in conducting AVA are gradually maturing. There is a need to ensure that AVAs are undertaken for relevant projects to avoid adverse impact, regardless whether it is a public or private sector project. Furthermore, the Wind Performance Criterion now provides a quantitative yardstick and methodological refinements to the AVAS. In view of the above, it is opportune to recommend extending the scope of application of the refined AVAS to include private sector projects. (b)There is a need to distinguish district-level from site-level projects. The district-level AVAs normally cover a relatively large area under planning and engineering feasibility study for new development areas, comprehensive land use restructuring scheme and area-wide plot ratio and building height control reviews, etc. Since the design schemes put under AVA testing are hypothetical and will not necessarily be the same as that finally implemented on site, the focus of AVA is less on the attainment of the Wind Performance Criterion, but more on comparing the wind performance of various development options for identifying measures to attain to a better wind environment. Normally, these AVA studies would be undertaken by government departments to ascertain the existing air ventilation condition and any required measures to promote urban permeability or mitigate any air ventilation concerns within the assessment area. The required measures shall be included in planning layouts or serve as development guidelines to project proponents in the implementation stage. In contrast, site-level AVAs are mainly to prove the acceptability of specific projects in air ventilation terms and propose mitigating design measures for improvement. (c) Developments would normally fully maximise their lot frontage wherever possible, particularly when there is a view to the harbour or the mountain. This may result in extensive wake area and hence adverse air ventilation impacts. Apart from waterfront sites, elongated inland sites may also induce similar adverse air ventilation impacts if the layout has not adequately incorporated permeability measures into the layout and buildings. An additional criterion to require these inland sites with lot frontage School of Architecture, CUHK Page 421 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT exceeding 140m in length is added as criterion (j) in the list of categories of projects. Qualitative Planning and Design Guidelines The existing AVA framework requires project proponents to carry out AVAs with a view to promoting layout / building permeability for a better ventilated pedestrian environment. Under the current Study, the framework is further refined and has incorporated a quantitative Wind Performance Criterion for assessing the acceptability of a development project in air ventilation terms. While air ventilation is a very important factor relevant to urban climate, there are other factors that are equally important, including green space, building volume, ground coverage, natural landscape, topography and proximity to openness. The Urban Climatic Planning Recommendation Map (UC-ReMap) has analysed and synthesised all these factors through the concept of PET and set out the urban climatic characteristics of different areas in Hong Kong. A total of 5 urban climatic planning zones and their respective strategic planning actions are proposed. Apart from serving as a strategic information platform, the UC-ReMap also provides the scientific context for understanding the urban climatic situation of local areas, the interaction of various factors and the resultant thermal comfort level and hence the recommended planning strategy for a better urban climate. In order to provide a set of focused and systematic guidelines for urban climatic improvement, which covers air ventilation as well as other urban climatic aspects, it is recommended that a new chapter be incorporated into the HKPSG to spell out the territorial and district urban climatic situations and considerations, as well as to strengthen planning and design guidelines for promoting good planning and design practices in working towards a better urban climate. The current Chapter 11 of the HKPSG on Urban Design Guidelines has already incorporated a section on ‗Air Ventilation‘ providing qualitative guidelines ―in land use planning, urban design, and planning and design of large scale developments in the early stages before any actual undertaking of air ventilation assessment‖. To consolidate all relevant considerations for a better urban climate, this ‗Air Ventilation‘ Section should be extracted to form part of a new HKPSG chapter. PART IV(B)-1 REVIEW OF THE AVA TECHNICAL CIRCULAR NO. 1/06 A review of the AVA Technical Circular has been conducted based on the findings of the Urban Climatic Map and completed AVAs. The purpose of the refined AVAS is to better assess the acceptability of proposed developments in air ventilation terms and identify School of Architecture, CUHK Page 422 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT necessary design improvement measures to mitigate any adverse impacts. The major refinements include: Policy Level Revisions (1) The scope of application of AVA should extend to cover all public and private developments meeting the criteria requiring AVAs. (2) The categories of sites that require AVA should be increased to include inland development sites with lot frontage over 140m. Methodological Revisions (3) The Wind Performance Criterion, which takes into account urban climatic considerations, should be incorporated as the quantitative yardstick for assessing the acceptability of air ventilation performance of proposed developments. (4) In addition to the use of wind velocity ratio (VR) as an indicator, the use of the indicator of median hourly mean wind speed (Vp) is recommended. (5) Summer condition should be analysed for design improvement for thermal comfort. (6) Standard Site Wind Availability Data should be provided for AVAs for consistent and accurate application. (7) In addition to overall assessment, area or point assessment should be conducted to tackle the weak wind conditions at sensitive areas. (8) Full documentation of the methodology and assumptions should be provided. (9) Technical issues, particularly for CFD test, should be resolved to ensure its reliability as a tool for AVA. Appendix 3 contains the details of proposed refinements to the AVA Technical Circular and Technical Guide. PART IV(B)-2 THE REVISED HKPSG 2.1 REVISIONS PROPOSED FOR HKPSG Since 2006, the HKPSG has incorporated a section on Air Ventilation in Chapter 11 ―Urban Design Guidelines‖ providing qualitative guidelines in land use planning, urban design, and planning and design of large scale developments in the early stages before any actual undertaking of air ventilation assessment. Guidelines at the district level and the site levels are included. It is suggested that the section on Air Ventilation be extracted from Chapter 11 of the HKPSG and combined with a new Section on Urban Climate to form a new Chapter in the School of Architecture, CUHK Page 423 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT HKPSG. This separate chapter shall provide a set of consolidated guideline on matters related to urban climate and air ventilation (see Appendix 4) PART IV(C) IMPLEMENTATION MECHANISM FOR THE REFINED AVAS PART IV(C)-1 PURPOSE This section reviews the approaches and experiences in implementing the current AVAS since 2006 and outlines the refined AVAS. The implementation of the refined AVAS through the existing development control mechanisms of the planning, land administration and building plan regimes is recommended. PART IV(C)-2 THE IMPLEMENTATION OF CURRENT AVAS SINCE 2006 2.1 Current implementation mechanisms for AVAS The approach of pioneering and encouraging, rather than regulating, have been adopted for implementing the current AVAS. Applicable government projects have since taken the initiative to conduct AVA in improving overall design. Initiatives for pioneering AVAS Initiatives Purposes Housing, Planning and Lands Bureau Mandating the relevant government projects to Technical Circular No. 1/06; Environment, carry out AVA and encourage the quasi- Transport and Works Bureau Technical government organisations and the private Circular No. 1/06 – Air Ventilation sector to apply AVA to their projects on Assessments voluntary and need basis. Incorporating a set of qualitative guidelines Providing general qualitative design guidelines for promoting air ventilation into Chapter for improving air ventilation in the preparation 11 of the Hong Kong Planning Standard and of town plans and development proposals. Guidelines Consideration of air ventilation at plan PlanD to undertake AVA to identify problem making stage areas for improvements on a district basis. Planning applications, review applications, Encourage proponents to undertake AVA to planning appeals, rezoning, representations. optimise the wind performance at site level. Land administration process, including new Encourage proponents to undertake AVA to lease, land exchange and lease modification optimise the wind performance at site level. Green building labeling system Provide incentive to project proponents to carry out AVA on a voluntary basis with BEAM accreditation. School of Architecture, CUHK Page 424 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT 2.2 Government Initiative for Pioneering AVAS Pursuant to the AVA Technical Circular No. 1/06, the Government has conducted AVA for major government projects. A public web-portal has also been created, in the form of the AVA registry, in promoting the knowledge base and transparency of the process. As of 14 September 2012, 73 government projects have completed or were still conducting AVA studies. The government departments/bureaux involved include Planning Department, Housing Department, Civil Engineering and Development Department, Transport and Housing Bureau, Architectural Services Department and Highways Department (please refer to Part IV(A)-2 of this report for an expert review of the AVAs). 2.3 Quasi-Government and the Private Sector Conducting AVA Quasi-government organisations and the private sector have also been actively undertaking AVA for individual development projects where practicable, with the Urban Renewal Authority committed to conduct AVA for any development involving more than 2 towers. The requirement for conducting AVA is now included in study brief for planning studies/feasibility studies which form the basis for preparation or amendment to town plans. Besides, some outline zoning plans (OZP) also stipulate the requirements for undertaking AVA for developments that may have significant implications on air ventilation. PART IV(C)-3 IMPLEMENTATION MECHANISM FOR REFINED AVAS Different mechanisms for implementing the refined AVAS have been assessed as follows. It is found that legislative control would not be suitable and the existing development control mechanisms through town planning, land administration and building plan submission is recommended. 3.1 Legislative Control Hong Kong is one of the pioneers in researching weak urban wind conditions. Since the establishment of the AVA framework, which is primarily intended to encourage applicants to improve the design of their developments in terms of its permeability, there have been some public requests to make air ventilation a mandatory requirement under legislative control. At present, there is no such legislative regime around the world. After thorough examination, the Study also concluded that it would not be suitable to recommend legislative control for the wind performance criterion because:- (a) The Wind Performance Criterion recommended is the first attempt to assess the School of Architecture, CUHK Page 425 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT acceptability of air ventilation impacts against a yardstick in Hong Kong. There are virtually no overseas experiences that could be relied on. Experiences have to be accumulated on the practical implementation issues for the Wind Performance Criterion. (b)Based on the benchmarking studies, there are some areas in Hong Kong that are currently unable to achieve a wind speed of 1 m/s due to a lack of site wind availability and the existing building morphology, e.g. Sheung Wan and Causeway Bay etc. As such, it is likely to be controversial to legislate the Wind Performance Criterion, which is applicable for the whole of Hong Kong. 3.2 Statutory and Administrative Control While legislative control is not appropriate given the above, the current development control system through town planning, land administration and building plan submission mechanisms should be adequate to ensure air ventilation consideration be properly considered during the planning and design process for both public and private projects listed in the Technical Circular. Only projects that could meet the Wind Performance Criterion would be considered as acceptable in air ventilation term. Town Planning The PlanD has already incorporated AVA as one of the planning considerations in OZP review, planning studies and determination of site development parameters, particularly the government land sale sites. Through AVA, air ventilation issues could be identified and addressed. The recommended improvement / mitigation measures, if necessary, would be imposed through relevant town plans and planning briefs to provide site specific guidance to the project proponent. If submission of planning application is required to obtain planning permission, and AVA is required under the OZP, planning brief or the Technical Circular, the project proponent would need to submit an AVA as part of the submission. The Town Planning Board can also stipulate the carrying out of AVA as one of the approval conditions. The planning control regime would ensure that planning proposals would take into account air ventilation at the early planning and design stage. There are, however, some development proposals that are always permitted under the OZP and need not undergo the planning application process. School of Architecture, CUHK Page 426 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Land Administration In the preparation of new lease conditions, land exchange and lease modifications, any developments having adverse implications on air ventilation, either due to the development scheme or the site circumstances, should be subject to AVA. The findings of the AVA shall serve as input in formulating the development parameters. This is particularly important when site intensification or amalgamation are effected through the land exchange or lease modification process and no planning application is required for the proposal. Currently, all the relevant government land sale sites have already been subject to the above arrangement. The same should be applied to private projects for land exchange and lease modifications which have air ventilation impacts. Building Plan Submission Under the new PNAP APP-152 ‗Sustainable Building Design Guidelines‘, the applicant has to satisfy three pre-requisite requirements, viz building separation, building setback and greenery in order to be granted the concessionary GFA for green and amenity features. If the site characteristics render it difficult to achieve the full compliance of building separation requirements, an applicant could submit an AVA justifying the alternative design. Hence, the applicant can have an additional alternative to demonstrate that the eventual design can meet the Wind Performance Criterion. PART IV(C)-4 AUTHORITIES AND TIMEFRAME OF IMPLEMENTATION With the establishment of the Wind Performance Criterion and the implementation of the revised AVAS, it is recommended that the concerned government bureaux/ departments should continue to be responsible for conducting, overseeing and self-appraisal of their own AVAs. AVAs for private developments shall be submitted to their respective approval authorities, e.g. AVA submitted in support of planning applications shall be vetted by PlanD to assist consideration by the TPB; AVA in support of building plan submission shall be vetted by the Building Authority. Subject to the endorsement of the study recommendations by the Government, the Wind Performance Criterion, and the refined AVAS shall take effect through the existing development control mechanisms. The new HKPSG Chapter on Urban Climate and Air Ventilation shall also be promulgated to guide project proponents in attaining to more responsive designs in urban climatic terms. School of Architecture, CUHK Page 427 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART IV(C)-5 REVIEW AND MONITORING The application of air ventilation assessment to regulate urban thermal comfort is a brand new subject for Hong Kong. With the introduction of the Wind Performance Criterion and the other methodological refinements, it would be useful to have regular reviews to monitor its effectiveness and to ensure that it is scientifically up-to-date. It is suggested that a review be conducted once every 5 years to assemble and analyse all submitted and documented projects to guage the experience in applying the Wind Performance Criterion and the refined AVA system, as well as take reference to relevant overseas experience in the field. Depending on the review, the AVA Technical Circular can be updated where necessary. It is recommended that a major ―scientific review‖ of Hong Kong‘s Wind Performance Criterion be conducted in 10 years‘ time. It is proposed that an expert committee led by PlanD be established for the review. Membership of the committee should include representatives from academia, the trade, professional organizations and government departments. School of Architecture, CUHK Page 428 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART IV(D) SUMMARY 1.1 OBJECTIVES The refined Air Ventilation Assessment System (AVAS) is based on key findings of the study and a review of selected completed AVAs carried out in accordance with the current AVAS. The Study recommends ways to refine the methodology in the AVAS Technical Circular No. 1/06, including the assessment standard, scope of application and implementation mechanisms. 1.2 KEY STUDY FINDINGS Key findings of the Study relevant to the refinement of AVAS include: (a) the need for a Wind Performance Criterion, (b) the importance of summer thermal comfort, (c) the importance of site wind availability including sea breezes, and (d) the importance to define the locations of test points having regard to the impact on the sensitive receivers. 1.3 LESSONS LEARNT FROM AN EXPERT REVIEW An expert review of selected, completed AVA studies under the current AVAS has been conducted. Lessons learnt include: (a) the need for studying summer condition, (b) the need for standardising site wind availability data, (c) the need for area and point analysis, (d) the need to resolving technical matters, and (e) the need of full documentation. 1.4 THE NEED OF A QUANTITATIVE YARDSTICK In the current AVAS, AVA is a design improvement tool with no quantitative yardstick. This approach is useful in its own right. With the formulation of the Wind Performance Criterion under the Study, it is now opportune to incoporate a quantitative yardstick to evaluate the acceptability of design options. 1.5 SCOPE OF APPLICATION OF THE AVA SYSTEM In the review of the implementation of the current AVAS, it is found that AVA has been carried out by both public and private project proponents. Expertise and experience in conducting AVAs are gradually maturing in Hong Kong. There is a need to ensure that AVA will be undertaken for both public and private projects, in order to avoid adverse ventilation impacts. In view of the above, it is now justified, feasible and practical to recommend extending the scope of application of the AVAS to include private sector projects. 1.6 KEY REFINMENTS TO THE AVAS The following key refinements to the AVAS have been proposed, and the Technical Circular and Technical Guide on AVA shall be revised accordingly: School of Architecture, CUHK Page 429 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (a) Extending the scope of application of AVA to private sector development. (b) The categories of sites that require AVA should be increased to include inland development sites with lot frontage over 140m. (c) Incorporating the Wind Performance Criterion as a quantitative yardstick to determine if the proposed development is acceptable in air ventilation terms. (d) In addition to the use of wind velocity ratio (VR), using the median hourly mean pedestrian level wind speed (Vp) as the main indicator. (e) Factoring the summer wind consideration into the AVAS. (f) Recommending the provision of a set of standardised Site Wind Availability Data by PlanD. (g) Choosing test points carefully to cover the air performance of frequently patronised locations and requiring more detailed area and point assessments and analysis. (h) Full documentation of the technical assumptions, inputs and procedures of AVAS for vetting and understanding by others. (i) To use CFD models appropriately. 1.7 NEW HKPSG CHAPTER Apart from the refinements to AVAS which are to be documented in the Technical Circular and Technical Guide on AVA, it is proposed to provide a set of qualitative planning and design guidelines to guide project proponents in working towards better urban climate and air ventilation. A new HKPSG chapter on ―Urban Climate and Air Ventilation‖ has been prepared to cover urban climatic and air ventilation considerations in planning. This chapter will cover all relevant matters relating to the Urban Climatic Maps and provide general guidelines on planning and design measures to improve urban climate and air ventilation. 1.8 IMPLEMENTATION MECHANISM The refined AVAS can be effected by the revised Technical Circular and Technical Guide on AVA and the new HKPSG chapter on ―Urban Climate and Air Ventilation―. It can be implemented through the current development control mechanisms of the town planning, land administration, and the building plan regimes. There is no need to introduce new legislation for implementing the refined AVAS. 1.9 REVIEW AND MONITORING With the introduction of the Wind Performance Criterion, other methodological refinements and the new HKPSG chapter, it is suggested that the AVAS be reviewed 5 years after its implementation to cater for any necessary updates. It is recommended that a major scientific review of Hong Kong‘s Wind Performance Criterion be conducted in 10 years‘ time. School of Architecture, CUHK Page 430 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT PART IV: APPENDICES School of Architecture, CUHK Page 431 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 1: HOUSING, PLANNING AND LANDS BUREAU TECHNICAL CIRCULAR NO. 1/06 AND ENVIRONMENT, TRANSPORT AND WORKS BUREAU TECHNICAL CIRCULAR NO. 1/06 ON AIR VENTILATION ASSESSMENTS School of Architecture, CUHK Page 432 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 433 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 434 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 435 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 436 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 437 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 438 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 439 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 440 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 441 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 442 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 443 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 444 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 445 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT School of Architecture, CUHK Page 446 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 2: A SUMMARY OF PROJECTS ON PLANNING DEPARTMENT AVA REGISTER AS OF SEPTEMBER 2010 School of Architecture, CUHK Page 447 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 3: THE PROPOSED AMENDMENTS TO THE TECHNICAL CIRCULAR FOR AVA Existing Technical Circular No. 1/06 for AVA Suggestion and Rationale 5. A framework for applying AVA is developed on the Since the promulgation of the basis of the ―Feasibility Study on Establishment of Air Technical Circular in July 2006, Ventilation Assessment‖ completed this year and both the public and private sector endorsed by the Committee on Planning and Land have proactively undertaken air Development on 7 June 2005. The Committee agreed that ventilation assessments to ensure Government will take the lead to apply AVA to all major that air ventilation issues are government projects which may have major impacts on properly considered in alternative the macro wind environment, including public housing development options. These AVAs projects, planning studies for new development areas and are proven to be practical and useful comprehensive redevelopment areas, preparation of new in improving designs. Expertise town plans and major revision to town plans. Quasi- and experience have been built up government organizations and the private sector are also in the past years. More importantly, encouraged to apply AVA to their projects on voluntary development proposals, no matter and need basis. public or private, may have air ventilation impacts and should equally be subject to AVA. As such, it is recommended to extend the scope of application of AVA to private sector developments to reflect the existing situation and recognise the efforts of the private sector. Taking into account the findings of the Urban Climatic Planning Recommendation Map, the AVA system should target at mitigating the negative urban climatic condition and hence focus on the Urban Climatic Planning Zones (UCPZ) 3, 4, and 5. The extensive UCPZ1 is either urban fringe or country parks that should be preserved and enhanced in order not to alter their positive urban climatic characteristics. 6. Proponent departments / bureau or authorities To further refine the AVA system, responsible for major government projects which may the wind performance criterion, bring about potential impact on air ventilation in the which adopts a flexible macro wind environment are strongly advised to include performance/prescriptive approach, AVA in the planning and design of projects. The main is proposed to serve as a yardstick purpose of AVA is to promote the awareness of project against which the acceptability of School of Architecture, CUHK Page 448 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT proponents to ensure that air ventilation impacts are duly air ventilation impacts can be considered as one of the main criteria in the planning and confirmed. The framework would design process. The framework developed at this stage still allow comparison of design does not provide an absolute benchmark standard against options in air ventilation terms and which the air ventilation impacts can be confirmed to be identification of potential problem acceptable or unacceptable. The framework would areas for design improvements. however, enable comparison of design options in external air ventilation terms and identification of potential problem areas for design improvements. A further study to develop benchmark standards for AVA in Hong Kong will be commissioned in 2006. Upon completion of the study and gaining sufficient experience, the AVA system may be refined. Projects Requiring AVA 7. For the purpose of this Technical Circular, government The listed categories of projects are projects refer generally to projects under the policy found to be adequate to cover initiatives, support or programmes of government projects which may have departments / bureaux / authorities e.g. public housing, implications on air ventilation government office buildings, footbridges etc.; regardless performance. AVA should be of their ownership. conducted to identify problem areas and design improvements as well as Proponent departments / bureaux or authorities should to confirm the project‘s assess the need to apply AVA to the following categories acceptability in air ventilation of major government projects during the planning stage terms. as early as possible: The paragraph should also be (a) Planning studies for new development areas; revised to include private sector (b) Comprehensive land use restructuring schemes, developments. including schemes that involve agglomeration of sites together with closure and building over of existing Apart from waterfront sites, inland streets; sites with elongated lot (c) Area-wide plot ratio and height control reviews; configuration may also induce (d) Developments on sites of over 2 hectares and with an adverse air ventilation impacts if the overall plot ratio of 5 or above; layout has not been adequately (e) Development proposals with total Gross Floor Area considered to incorporate exceeding 100,000 square metres; permeability into the building and (f) Developments with podium coverage extending over layout. It is suggested to add an one hectare; additional criterion as below:- (g) Developments above public transport terminus; (h) Buildings with height exceeding 15 metres within a Developments on non-waterfront public open space or breezeway designated on layout sites with lot frontage exceeding plans / outline development plans / outline zoning 140 metres in length. plans or proposed by planning studies ; (i) Developments on waterfront sites with lot frontage Rationale: A long frontage (140m) exceeding 100 metres in length; may have adverse air ventilation School of Architecture, CUHK Page 449 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (j) Extensive elevated structures of at least 3.5 metres impacts. 140m is calculated based wide, which abut or partially cover a pedestrian on the resultant frontage of a corridor along the entire length of a street block that “square-shaped site of 2 hectares”, has / allows development at plot ratio 5 or above on as in (d). The frontal dimensions both sides; or which covers 30% of a public open and therefore the potential impact space to the wind environment for wind coming perpendicular to them are therefore similar in both cases. 8. The above list is not exhaustive and proponent No Change departments / bureaux or authorities may exercise their discretion to include specific projects within their jurisdiction as appropriate. 9. In assessing the need for AVAs for individual projects, Suggested to delete point(g) as the the proponent departments / bureaux or authorities should AVAS has already been in place for also take into account the following factors : 6 years. Therefore, point(g) should (a) Whether there are existing / planned outdoor sensitive not be relevant anymore. receivers located in the vicinity of the project site falling within the assessment area. The sensitive receivers should include pedestrians or open space users; (b) Whether there are known or reasonable assumptions of the development parameters available at the time to conduct the AVA; (c) Whether alternative designs are feasible or alternative locations are available for the project if the AVA to be conducted would reveal major problem areas; (d) Whether there are other overriding factors which would prevail over air ventilation considerations in the determination of the project design; (e) Whether the desirable project design for better air ventilation may compromise other important objectives for the benefits of the public; (f) Whether the public has raised concern on air ventilation in the neighbourhood area of the project; and /or (g) Whether the project is already in advanced stage to incorporate the AVA. 10. An officer of D2 rank or above of the proponent No change departments/bureaux or authorities should be responsible for deciding whether AVA is necessary for the government project. If it is decided that the AVA shall be waived, strong justifications should be provided and it is necessary to obtain agreement of the respective policy School of Architecture, CUHK Page 450 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT bureau. If the AVA is considered necessary but pre- mature, a recommended timing or stage of the project for carrying out the AVA should be indicated. 11. For government projects waived from the AVA AVA for private projects should requirement, the proponent departments / bureaux or also be uploaded to the AVA authorities should, as good practice, still incorporate register and kept for 3 years, and appropriate qualitative design guidelines to minimize thereafter archived. The relevant impacts on air ventilation. authority should be responsible for These qualitative design guidelines are available in the co-ordinating the submission of ―Urban Design Guidelines‖, Chapter 11 of the Hong AVA by private parties. Kong Planning Standards and Guidelines, downloadable from Planning Department‘s (PlanD) homepage Full documentation of the AVAs, http://www.pland.gov.hk. including all important model settings, input parameters, pre- tests, is needed to facilitate checking and review. PROPOSED AMENDMENTS TO THE AVA TECHNICAL GUIDE Technical Guide for AVA for development Suggestions and rationale in Hong Kong 1. This Technical Guide assists project No change proponent to undertake Air Ventilation Assessment (AVA) to assess the impacts of the proposal on the pedestrian wind environment. The assessment should follow this Technical Guide as far as possible and a report should be submitted to the proponent departments / bureaux or authorities on the assessment findings 2. Every site is different. The assessor is No change strongly advised to approach the assessment intellectually and discretionally taking into account different site conditions. Working with experienced practising wind engineers throughout the assessment process is strongly recommended. Indicator 3. Wind Velocity Ratio (VR) should be used Annual and Summer median hourly mean as an indicator of wind performance for the pedestrian level wind speed (Vp) should be AVA. It indicates how much of the wind used as the key indicator of wind availability of a location could be performance for AVA. Given the general School of Architecture, CUHK Page 451 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT experienced and enjoyed by pedestrians on weak wind conditions in Hong Kong, the ground taking into account the surrounding higher the Vp, the less likely the impact of buildings and topography and the proposed the proposed development on air ventilation. development. Given the general weak wind conditions in Hong Kong, the higher the In addition, Wind Velocity Ratio (VR) wind velocity ratio, the less likely would be should also be documented and reported for the impact of the proposed development on cross referencing purpose. the wind availability. Rationale: this is in line with the Wind Performance Requirement of the Wind Performance Criterion. 4. Wind VR is defined as Vp/Vinf (V Vp captures the wind performance at the pedestrian/V infinity). Vinf captures the wind pedestrian level (2 m above ground) after velocity at the top of the wind boundary layer taking into account the effects of buildings, (typically assumed to be around 400 m to 600 urban and topographical features. m above city centre, or at a height wind is unaffected by the urban roughness below). To improve accurancy, the VR can be Vinf is taken as the wind availability of the calculated based on the site wind availability site. Vp captures the wind velocity at the (Vs) of the site. Vs is the site wind pedestrian level (2 m above ground) after availability at the top of the urban roughness taking into account the effects of buildings sub-layer (RSL). It takes into account the and urban features. modification of Vinf due to surrounding topography. Rationale: the understanding here elaborates on the terminologies used and is in line with the recommended wind performance criterion. [Remarks: VR will still be useful as a design reference and an indicator of the permeability of the layout, whereas the Vp will be the key performance criterion taking into account both the effect of site wind availability and the layout permeability.] Expert Evaluation / Initial Study / Detailed Study 5. It is always useful and cost effective for Expert Evaluation is particularly useful for the assessor to conduct an early round of the following categories under ―projects Expert Evaluation. This provides a requiring AVA‖: qualitative assessment to the design and/or design options and facilitates the (a) Planning studies for new development identification of problems and issues. The areas; School of Architecture, CUHK Page 452 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Expert Evaluation is particularly useful for (b) Comprehensive land use restructuring large sites and/or sites with specific and schemes, including schemes that involve unique wind features, issues, concerns and amalgamation of sites together with problems. closure and building over of existing streets; and (c) Area-wide plot ratio and height control reviews. It provides strategic and district wide understanding for planners to optimise urban air ventilation at the district and OZP levels. For district level planning decision making, Expert Evaluation is more suitable in guiding the process as, unlike AVA Initial and Detailed Studies, it does not require any detailed particulars of buildings at the site level – which is normally unavailable. Based on existing literature, Expert Evaluation employs parametric understanding of the urban morphological characteristics, e.g. the height to width ratios of the street, to evaluate the resultant flow regimes, and to make recommendations to planners. At the district level, directionalities of the flow regime and flow characteristics are more important than the precise quantities. If deemed necessary by the experts, suitable quantitative wind flow studies and AVAs may assist the expert evaluation exercise. Rationale: Based on the AVA experience gained so far as reviewed earlier. The following tasks may be achieved with To conduct the Expert Evaluation Expert Evaluation: systematically and methodologically, it is necessary to undertake the following (a) Identifies good design features. information analyses: (a) Analyse relevant wind data as the input (b) Identifies obvious problem areas and conditions to understanding the wind propose some mitigation measures. environment of the study area. (b) Analyse the topographical features of the (c) Defines ―focuses‖ and methodologies study area, as well as the surrounding areas. of the Initial and/or Detailed studies. (c) Analyse the greenery/landscape characteristics of the study area, as well as the surrounding areas. School of Architecture, CUHK Page 453 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (d) Determines if further study should be (d) Analyse the land use and built form of the staged into Initial Study and Detailed study area, as well as the surrounding areas. Study, or Detailed Study alone. (e) Estimate the characteristics of the input wind conditions of the study area. (f) Identify the wind flow characteristics of the study area, and problematic areas which warrant attention. Identify existing ―good features‖ that need to be kept or strengthened. Based on the understanding on the existing condition: (a) Analyze the impacts of the proposed development on its surroundings; (b) Highlight problem areas, good design features if any, and recommend improvements and mitigation measures if possible. (c) Identify focus areas or issues that may need further studies. Recommend appropriate technical methodologies for the study if needed. Rationale: Based on the AVA experience gained so far as reviewed earlier. 6. In exercising expert knowledge and No change experience, the assessor should refer to the ―Urban Design Guidelines‖, Chapter 11 of the Hong Kong Planning Standards and Guidelines downloadable from the Planning Department‘s (PlanD) website at http://www.pland.gov.hk. 7. The Expert Evaluation could lead to an Suggest changing to: Initial Study or directly to a Detailed Study depending on the nature of the development. 7. The Expert Evaluation could lead to an The Initial Study will refine and substantiate Initial Study or directly to a Detailed Study the Expert Evaluation. The following tasks depending on the nature of the development. may be achieved with the Initial Study: For projects that could not meet the Wind Performance Requirement, provided that the (a) Initially assesses the characteristics of non-compliance could be demonstrated as the wind availability (Vinf) of the site. being attributed to the topography and / or built environment surrounding the proposed (b) Gives a general pattern and a rough development, the Alternative (Prescriptive) quantitative estimate of wind Approach of the Wind Performance Criterion performance at the pedestrian level can be adopted. Initial Study could be used reported using Wind VR. for such purpose and help optimise the School of Architecture, CUHK Page 454 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT benefits of the four prescribed mitigating (c) Further refines the understanding design measures through options comparison. (good design features and problem areas) Under these circumstances, Detailed Study of the Expert Evaluation. may not be necessary. The following tasks may be achieved with the Initial Study: (d) Further defines the ―focuses‖, methodologies and scope of work of the (a) Based on the wind availability of the site, Detailed Study. identify the key prevailing wind directions (that represent at least 75% of the wind directional frequency or 8 of the 16 wind directions) of the study area. All the wind directions identified should be analyzed separately. (b) Conduct the study and give a general pattern and a rough quantitative estimate of wind performance at the pedestrian level reported, using Wind Vp and Wind VR. (c) Highlight good design features and problem areas, if any. Recommend practical improvements and optimizing design mitigation measures if possible. Re-test and re-study if necessary. (d) Further refine the understanding (on good design features and problem areas) of the Expert Evaluation, if applicable. (e) Further define the ―focuses‖, methodologies and scope of work of the Detailed Study if needed. 8. It is sometimes necessary to reiterate the No change Initial Study so as to refine the design and/or design options. 9. With or without the Initial Study, the The following tasks may be achieved with Detailed Study concludes the AVA. With the Detailed Study: the Detailed Study, the assessor could accurately and ―quantitatively‖ compare (a) Based on the Site Wind Availability of designs so that a better one could be selected. the site, conduct a quantitative Detailed Study is essential for more complex assessment based on all the 16 wind sites and developments, and where key air directional frequency to confirm if the ventilation concerns have been reviewed and wind performance criterion could be met. identified in the Expert Evaluation / Initial (b) In case the wind performance criterion Study. The following tasks may be achieved could not be met, test out alternative with the Detailed Study: design measures to improve the wind performance. (a) To assess the characteristics of the wind (c) To report all the annual and summer availability (Vinf) of the site median hourly mean pedestrian level Vp School of Architecture, CUHK Page 455 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT in detail. and VR of test points. To report Site Vp (SVp), Local Vp (LVp), Site VR (SVR), (b) To report all VR of test points. To report Local VR (LVR) when appropriate. Site VR (SVR) and Local VR (LVR) when (d) To report any wind gust problems. appropriate (as outlined in paras 27 to 30). (e) To report, if any, problems identified To report, if any, wind gust problems. when examining the individual test points. (c) To provide a summary of how the (f) To provide a summary of how the identified problems, if any, have been identified problems, if any, have been resolved. resolved through effective design improvement measures. Rationale: Based on the AVA experience gained so far as reviewed earlier. Site Wind Availability Data 10. It is necessary to account for the For AVA study, the set of Site Wind characteristics of the natural wind availability Availability (Vs) data to be provided on of the site. As far as possible, the design PlanD‘s website should be used. should utilize and optimise the natural wind. Based on the data, project proponent and their consultants may additionally wish to, if necessary, further refine the dataset to account for any specific features identified. This further understanding must be properly justified and documented. 11. For the Expert Evaluation, it is advisable Suggest to be deleted to make reference to the Hong Kong Observatory Waglan Island wind data, as well as reasonable wind data of nearby Rationale: as PlanD is expected to produce weather stations. Expertly interpreted, it is a set of site wind availability data (Vs) and possible to qualitatively estimate the refinement procedures. prevailing wind directions and magnitudes of the site necessary for the evaluation. 12. For the Initial Study, it is necessary to be more precise. Either ―simulated‖ site wind data, or ―experimental‖ site wind data, as described in paras. 13 and 15 below, respectively, could be used. 13. Using appropriate mathematical models (e.g. MM5 and CALMET), it is possible to simulate and estimate the site wind availability data (Vinf). For the Expert School of Architecture, CUHK Page 456 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Evaluation and Initial Study, project proponent may refer to the preliminary set of simulated ―Site Wind Availability Data‖ (Vs) available at PlanD‘s website. 14. For the Detailed Study, it is necessary to Suggest to be deleted be even more precise. ―Experimental‖ site wind data, as described in para 15 below, should be used. Rationale: as PlanD is expected to produce a set of site wind availability data (Vs) and 15. Using large scale topographical model refinement procedures. (typically 1:2000 to 1:4000) tested in a boundary layer wind tunnel, more precise wind availability and characteristics information in terms of wind rose, wind profile(s) and wind turbulence intensity profile(s) of the site could be obtained. Hong Kong Observatory Waglan Island wind data should be referenced to for the experimental study. Tools 16. Wind tunnel is recommended for both the No change Initial and the Detailed Studies, and most particularly for the Detailed Study. The conduct of the wind tunnel test should comply, as far as practicable, with established international best practices, such as, but not be limited to: (a) Manuals and Reports on Engineering Practice No. 67: Wind Tunnel Studies of Buildings and Structures, Virginia 1999 issued by American Society of Civil Engineers. (b) Wind Engineering Studies of Buildings, Quality Assurance Manual on Environment Wind Studies AWES-QAM-1-2001 issued by Australasian Wind Engineering Society. 17. Computational Fluid Dynamics (CFD) Computational Fluid Dynamics (CFD) may may be used with caution; it is more likely be allowed for AVA Initial Studies. CFD for admissible for the Initial Studies. There is no Initial Studies shall be used mainly for internationally recognized guideline or ―patterns‖ of wind environment within the School of Architecture, CUHK Page 457 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT standard for using CFD in outdoor urban assessment areas. International best practice scale studies. The onus is on the assessor to such as the following should be referred to: demonstrate that the tool used is ―fit for the purpose‖. Franke, J., Hirsch, C., Jensen, A. G., Krus, H. W., Schatzmann, M., Westbury, P. S., Miles, S. D., Wisse, J. A., Wright, N. G., (2004), Recommendations on the Use of CFD in Predicting Pedestrian Wind Environment‗, COST Action C14, Impact of Wind and Storms on City Life and Built Environment, Working Group 2 CFD techniques 2004 version 1.0 Michael Schatzmann, Helge Olesen and Jörg Franke, COST Action 732 – Quality Assurance and Improvement of Microscale Meteorological Models, Feb 2010. ISBN: 3-00-018312-4. VDI, (2005) Environmental Meteorology - Prognostic Microscale Wind field Models - Evaluation For Flow Around Buildings And Obstacles, VDI/DINHandbuch Reinhaltung der Luft. Beuth, Berlin, 53 pp. VDI 3783 part 9. Tominaga, Y., Mochida, A., Yoshie, R., Kataoka, H., Nozu, T., Yoshikawaf, M. and Shirasawac, T., (2008) AIJ guidelines for practical applications of CFD to pedestrian wind environment around buildings, Journal of Wind Engineering and Industrial Aerodynamics 96 (2008) 1749–1761. 18. Should the assessor wish to use other No change forms of tool for the assessment not described above, the onus is on the proponent to demonstrate that the tool to be employed is ―fit for the purpose‖. The scientific suitability, as well as the practical merits of the tool to be used must be demonstrated. Simplification of Wind Data for the Initial Study 19. In general, the characteristics of the site 75% of the time typically means 8 directions wind availability data should be reported in of the full 16 directions. The project 16 directions. This is necessary to work out proponent must document this simplification the Wind Velocity Ratio. and produce ―the simplified site wind School of Architecture, CUHK Page 458 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT 20. For the Initial Study, if using CFD, it may availability data‖ used for the Initial Study. be appropriate and cost effective, to reduce the number of directions in the study. This is reasonable especially for sites with only a few incoming prevailing wind directions. The assessor must demonstrate that the probability of wind coming from the reduced set of directions should exceed 75% of the time in a typical reference year. Wind profile(s) for the site could also be appropriated from the Vinf data developed from simulation models (e.g. MM5 and CALMET) and with reference to the Power Law or Log Law using coefficients appropriate to the site conditions. 21. For the Detailed Study, no simplification is allowed. Wind from all 16 directions and their probability of occurrences must be accounted for, and wind profiles(s) obtained from wind tunnel experiments should be used to conduct the study, and when calculating the Wind Velocity Ratio. Project, Assessment and Surrounding No change Areas 22. The testing model for the Initial and the Detailed Studies should cover the Project, the Assessment and the Surrounding Areas. 23. The Project Area is defined by the project site boundaries and includes all open areas within the project that pedestrians are likely to access. 24. A key aim of AVA is to assess a design‘s The assessment area should be large enough impact and effects on its surroundings. The to capture the important ventilation effects of Assessment Area of the project should the proposed development, particularly for include the project‘s surrounding up to a development surrounded by open spaces in perpendicular distance H from the project its vicinity, the effects of the development boundary, H being the height of the tallest will be extended beyond the open spaces and building on site. Occasionally, it may be up to the built up areas in the surrounding. necessary to include an assessment area larger than that defined above so that special surrounding features and open spaces are not omitted. School of Architecture, CUHK Page 459 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT 25. For the model, it is necessary to include Other than the method recommended, wind areas surrounding the site. The Surrounding engineers can advise alternative extent of the Area is important as it gives a reasonable and Surrounding Area to be included on a case- representative context to the Assessment by-case basis, especially when there are Area. It ―conditions‖ the approaching wind nearby prominent topographical, and urban profiles appropriately. If the Surrounding morphological features. Area is not correctly included and modeled, the wind performance of the Assessment Area will likely to be wrongly estimated. The Surrounding Area of up to a perpendicular distance of 2H from the project boundary must be included. Sometimes it may be necessary to enlarge the Surrounding Area if there are prominent features (e.g. tall buildings or large and bulky obstructions) immediately outside the 2H zone. Other than the method recommended, wind engineers can advise alternative extent of the surroundings to be included on a case-by- case basis, especially when there are nearby prominent topographical features. Test Points The test points should be: 26. Test points are the locations where Wind VRs are reported. Based on the VR of the test (1) Evenly distributed in publically points, the resultant wind environment of the accessible areas. project can be assessed. As each site is (2) With a focus at important locations that unique, it is impossible to be specific about are frequented by pedestrians, including the number and distribution of the required streets and open spaces where people test points; but they must be carefully and congregate, and building entrances etc. strategically located. Three types of test points may be specified Three types of test points may be specified for assessment: Perimeter, Overall and for assessment: Perimeter, Overall and Special. Special. 27. Perimeter test points are positioned on the For a 2 ha site, typically about 30 to 50 well project site boundary. They are useful to spaced out and located perimeter test points assess the ―immediate‖ effect of the project will suffice. to the Assessment Area. Test points at around 10 m to 50 m center to center (or more if larger test site is evaluated) may be located around the perimeters of the project site boundary. Test points are normally not necessary at perimeter(s) where there is no major air ventilation issues e.g. waterfront School of Architecture, CUHK Page 460 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT area with ample sea breeze, inaccessible land such as green belt. Tests points must be located at the junctions of all roads leading to the project site, at main entrances to the project, and at corners of the project site. This group of perimeter test points will provide data for the Site Air Ventilation Assessment. Typically about 30 to 50 perimeter test points well spaced out and located will suffice. 28. Overall test points are evenly distributed Roughly 50% of all the overall test points and positioned in the open spaces, on the must be located no further than 0.5H from streets and places of the project and the boundary of the project site within the Assessment Areas where pedestrians assessment area. This is to better capture the frequently access. This group of overall test impact of wind wakes nearer to the project points, together with the perimeter test site. points, will provide data for the Local Air Ventilation Assessment. For practical This group of overall test points, not reasons, around 50 to 80 test points may be including perimeter test points, will provide adequate for typical development sites. data for the Local Air Ventilation Assessment. For practical reasons, around 50 to 80 test points may be adequate for project sites of two hectares in size. 29. Special test points may be positioned in Should also mention Vps. areas that special localized problems are likely to appear (e.g. wind gust problem for exposed sites). These special test points should not be included in the Site and Local Air Ventilation Assessments, as they may distort the average VRs. They independently may provide additional information to assessors. Reporting 30. For the purpose of the AVA, Wind For the purpose of AVA, Summer Vp and Velocity Ratios of all test points should be VR [1 June to 31 Aug] and annual Vp and individually reported. They help to identify VR of all test points should be individually problem areas. reported. The summer Vp (sVp) and the annual Vp (aVp) reported will be used to Two ratios may also be reported, they give a check against the conditions of the Hong simple quantity to summarise the overall Kong Wind Performance Criterion, i.e. the impact on the wind environment for easy Summer (1 Jun - 31 Aug) and annual median School of Architecture, CUHK Page 461 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT comparison: hourly mean wind speed should be no less than 1 m/s. (a) For the Site Air Ventilation Assessment, the Site spatial average As a good practice, a table of annual and Velocity Ratio (SVR) of all perimeter test summer Vpi and VRi of the directions tested points (para 27 refers) may be reported. should also be appended to the report for This gives a hint of how the development further checking when necessary. proposal impacts the wind environment of its immediate vicinity. Furthermore, for design refinement, FOUR ratios may also be reported, they give a (b) For the Local Air Ventilation simple quantity to summarise the overall Assessment, the Local spatial average impact on the wind environment for easy velocity ratio (LVR) of all perimeter and comparison: overall test points (paras 27 and 28, respectively refer) may be reported. This (a) For the Site Air Ventilation Assessment, gives a hint of how the development the annual and summer Site spatial average proposal impacts the wind environment Velocity Ratio (SVR) of all perimeter test of the local area. points may be reported. This gives a hint of how the development proposal impacts on The local air ventilation considerations the wind environment of its immediate should always take precedence over the site vicinity. specific air ventilation considerations. For exposed sites, concerns of wind gust should (b) For the Site Air Ventilation Assessment, be reported. the annual and summer Site spatial average Vp (aSVp and sSVp respectively) of all perimeter test points may be reported. This gives a hint of how the development proposal impacts on the wind environment of its immediate vicinity. (c) For the Local Air Ventilation Assessment, the annual and summer Local spatial average velocity ratio (LVR) of all overall test points may be reported. This gives a hint of how the development proposal impacts on the wind environment of the local area. (d) For the Local Air Ventilation Assessment, the annual and summer Local spatial average Vp (aLVp and sSVp respectively) of all overall test points may be reported. This indicates how the development proposal impacts on the wind environment of the local area. 31. The AVA report should contain the For the Initial and the Detailed Studies, A following key sections. The technical merit, section on the methodology, approach, input School of Architecture, CUHK Page 462 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT as well as the results of the AVA of the assumptions, settings, software and project must be demonstrated: equipments should be included. For CFD (a) An introductory section of the details of models, the domain, modelling size and the project. details, meshing approach, mesh size, (b) A section on results of the Expert expansion ratio, blockage ratio, numerical Evaluation. Concerns and potential scheme, convergence factor, turbulence problems should be identified. Focuses and model, approach wind profiles and other methodologies of further studies should be relevant technical information should be defined. reported. For wind tunnel tests, the wind (c) A section on the characteristics of the Site profile, turbulence intensity profile, the Wind Availability to be used for Initial power density spectrum, wind speed, the Studies and Detail Studies. Methodologies equipment used and the results of their pre- used to obtain the information must be test calibration should be reported. In explained in detail. addition, the matching according to the (d) A section on the Methodology of the model scale, the eddy sizes and longitudinal, Initial Study. The tool used for the studies lateral and vertical wind direction must be explained in detail. It is important fluctuations may also be included to improve for the assessor to demonstrate and to justify the scientific validity of the tests. If it is pre- that the tool and work process used is tested for Reynolds Number independence technically ―fit for the purpose‖. before the actual test, and that similarity of (e) A section on results and key findings of flow has been ensured, then this should be the Initial Study. documented. (f) A section on Methodology of the Detailed Study. The tool used for the studies It is important for the assessor to demonstrate must be explained in detail. It is important and justify that the tool and work process for the assessor to demonstrate and to justify used is technically ―fit for the purpose‖. that the tool and work process used is International best practice should be referred technically ―fit for the purpose‖. to. (g) A section on results and key findings of the Detailed Study. (h) A section on Evaluation and Assessment. Summarise findings, highlight problems and outline mitigation measures, if any. School of Architecture, CUHK Page 463 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Suggest changing to: 32. Based on the reported VR, the assessor Based on the reported annual and summer would compare the merits and demerits of Vp, the project proponent should be able to different design options. demonstrate if the proposal satisfies the Hong Kong Wind Performance Criterion. The following considerations on the reporting of SVR and LVR may be useful to The following considerations on the note: reporting of Vp/VR, aSVp/sSVp, aSVR/ sSVR, aLVp/sSVp and aLVR/ sSVR may be useful to note: (a) In the general weak wind conditions in Hong Kong, for the AVA, the higher the (a) In the general weak wind conditions in values of the spatial average VR, the better Hong Kong, for the purpose of AVA, the the design. Comparing performances of higher the values of the spatial average Vp design options using the spatial average VR and VR, the better the overall design. (both SVR and LVR) is recommended (para 30 refers). (b) The Site Air Ventilation Assessment (SVp/SVR) that includes aSVp/sSVp and (b) The Site Air Ventilation Assessment aSVR/sSVR gives an idea of how the lower (SVR) gives an idea of how the lower portion portion of the buildings on the project site of the buildings on the project site may affect may affect the immediate surroundings. the immediate surroundings. When problems When problems are detected, it is likely that are detected, it is likely that design changes design changes may be needed for the lower may be needed for the lower portion of the portion of the development (e.g. the coverage development (e.g. the coverage of the of the podium) (para 30(a) (b) refers). podium) (para 30(a) refers). (c) The Local Air Ventilation Assessment (c) The Local Air Ventilation Assessment (LVp/LVR) that includes aLVp/sLVp and (LVR) gives an idea of how the upper portion aLVR/sLVR gives an idea of how the upper of the buildings on the project site may affect portion of the buildings on the project site the surroundings. When problems are may affect the surroundings. When problems detected, it is likely that design changes may are detected, it is likely that design changes be needed for the upper portion of the may be needed for the upper portion of the development (e.g. re-orientation of blocks development (e.g. re-orientation of blocks and adjustment to the extent of the towers) and adjustment to the extent of the towers) (para 30(b) refers). (para 30(c) (d) refers). Suggest changing to: (d) For very large sites, or for sites with (d) For large sites, or for sites with elongated elongated or odd geometry, it or odd geometry, it may be necessary to work may be necessary to work out the SVR and out the SVp/LVp and SVR/LVR to suit the LVR to suit the size or geometry. For size or geometry. For example, for an example, say for an elongated site, it might elongated site, it might be useful to sub- be useful to sub-divide the site into smaller divide the site into smaller sub-sections to sub-sections to work out the spatial averages. work out the spatial averages. It is possible School of Architecture, CUHK Page 464 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT It is possible that the development may have that the development may have a high Vp at a high VR at one end and a low VR at the one end and a low Vp at the other end. other end. (f) High Vp indicates wind amplification, and (e) It is necessary to examine VR of the the possibility of wind gust and pedestrian individual test points of SVR and/or LVR to safety concerns. 40 Further assessments and ensure that none is way below the spatial mitigation measures may be required. average. When this happens, it indicates possible stagnant zones to be avoided. (g) Where large differentials in individual Vp and VR are reported, the spatial average SVp (f) On the other hand, no individual VR and/or LVp and SVR and/or LVR should be should be obviously above the spatial interpreted more carefully to avoid potential average SVR and/or LVR. When this overlooking of problem areas due to happens, it indicates wind amplification, and averaging of the individual Vp/VR. the possibility of wind gust and pedestrian safety concerns. Further assessments and (h) In addition to SVp/LVp and SVR/LVR, mitigation measures may be required. and beyond the key focus of AVA in this Technical Guide, Vp of special test points, if (g) Where large differentials in individual positioned, may be analysed. The results VRs are reported, the spatial average SVR from these additional test points will identify and/or LVR should be interpreted more potential wind problems in areas of special carefully to avoid overlooking problem areas concerns. due to averaging of the individual VRs. (h) In addition to SVR and LVR, and beyond the key focus of AVA in this Technical Guide, VR of special test points, if positioned, may be analysed. The results from these additional test points will identify potential wind problems in areas of special concerns. 40 For gust wind assessment, refer to: Melbourne, W.H. (1978) Criteria for Environmental Wind Conditions. Journal of Industrial Aerodynamics, Vol. 3, pp 241-249, Elsevier. And Hunt, J.C.R, Poulton, E.C., Mumford, J.C. (1976) The Effects of Wind on People; New Criteria Based on Wind Tunnel Experiments. Building and Environment. Vol, 11 pp 15-28, Pergamon Press. And Penwarden, A.D. and Wise, A.F.E. (1975). Wind environment around buildings. Building Research Establishment Report, HMSO, London. And Soligo, M.J., Irwin, P.A., Williams, C.J. and Schuyler, G.D. (1998) A comprehensive assessment of pedestrian comfort including thermal effects. Journal of Wind Engineering and Industrial Aerodynamics, Vol. 77/78, pp. 753-766, Elsevier. School of Architecture, CUHK Page 465 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 4: REVISIONS PROPOSED FOR HKPSG New Chapter on Urban Climate and Air Ventilation Section A : Background, Scientific Understanding, Goal and Objectives, Scope and Application Section B: Urban Climatic Planning Recommendation Map Section C: General Guidelines on Planning and Design Measures to Improve Urban Climate and Air Ventilation, Air Ventilation Assessment Section D: Conclusion Appendix : Methodology for Urban Climatic Planning Recommendation Map For the new section on Urban Climate, the following information may be included: Section A: Background, Scientific Understanding, Goal and Objectives, Scope and Application A.1 Introduction Hong Kong is located at a sub-tropical region with hot and humid summer months, and is one of the most densely populated cities in the world. As a result of the dense concentration of urban activities and development, Hong Kong is suffering from the Urban Heat Island (UHI) effects. To target for long-term improvements to the living environment, the Planning Department has completed the ―Feasibility Study for Establishment of Air Ventilation Assessment System‖ (the AVA Study) in 2005 and the ―Urban Climatic Map and Standards for Wind Environment – Feasibility Study‖ (the UCM Study) in 2012. On the basis of the findings and recommendations of the above two Studies, an urban climatic planning framework for Hong Kong, a set of qualitative guidelines outlining the planning and design measures conducive to a better urban climate, and a refined Air Ventilation Assessment (AVA) System have been formulated and outlined in this chapter to guide planning and design of future developments. School of Architecture, CUHK Page 466 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT A.2 Background The Team Clean Report, published in August 2003 after the severe acute respiratory syndrome (SARS) outbreak, recommended to promote better layout of building blocks through examining the stipulation of AVA as one of the considerations for all major development or redevelopment proposals and in forward planning. Accordingly, the Planning Department commissioned the AVA Study, which was completed in 2005, and on the basis of its recommendations,an AVA system has since been established. To enhance the urban wind environment, especially to the public realm, a set of qualitative guidelines on air ventilation assessment were included in the Urban Design Guidelines (i.e. Chapter 11 of the HKPSG) in July 2006 based on the AVA study recommendations. The revised urban design guideline in the chapter was also a response to the Government‘s First Sustainable Development Strategy promulgated in May 2005, which identified, amongst others, the need of guidelines governing sustainable urban planning and design, with special regard to issues such as buildings affecting view corridors or restricting airflow. The AVA Study identified the need for a more holistic review of urban climatic conditions for better planning decision-making at the territorial and district levels. In tandem, the Planning Department commissioned the UCM Study to examine urban climatic conditions in the whole territory and to identify appropriate planning and design measures to achieve long- term improvement of the urban climate. With the objective of alleviating the UHI effect, the UCM Study recommended, amongst others, the establishment of an Urban Climatic Planning Recommendation Map (UC-ReMap), a set of qualitative planning and design measures to improve the urban climate, a Wind Performance Criterion and a refined AVA System. A.3 Scientific Understanding Urban areas, with a high concentration of concrete buildings and other man-made structures, have their own urban climatic conditions that differ quite considerably from rural and natural areas. By virtue of its building morphology, thermal capacity and surface materials used in construction, urban areas typically gain more heat during daytime than the rural surroundings. The heat stored will elevate urban temperature. Tall buildings in the urban area block the sky view and limit the ability of the urban area to release heat back into the atmosphere during night time. The residual heat carries forward to the following day and the vicious circle continues, resulting in higher urban temperature. This is known as the UHI effect. Further, the urban area, with its tall buildings, has a higher ground roughness. Wind will flow over it more slowly, thus weakening urban air ventilation in addressing the UHI. UHI effect School of Architecture, CUHK Page 467 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT contributes to uncomfortable urban living, heat stress, heat-related health issues and increase in energy consumption, especially during the hot summer months. Overall, this has resulted in poorer quality of urban living. Figure IV-1 Urban Heat Island Effect Human thermal comfort is the focus of planning for a better climate. It is influenced by a number of environmental factors like air temperature, radiation, wind speed and so on. Thermal comfort can be quantified using Physiological Equivalent Temperature (PET). PET is a widely adopted synergetic indicator of human thermal comfort based on a combination of environmental variables and physiological inputs. The PET value that one expresses a neutral thermal sensation, i.e. neither cool nor warm, is known as the neutral PET (nPET). According to the UCM Study‘s Users‘ Thermal Comfort Survey, the nPET for Hong Kong under the summer conditions is 28oC. This nPET forms the benchmark for attaining urban thermal comfort in Hong Kong. There are many factors that could help improve thermal comfort. From planning and urban design perspectives, wind and thermal load are the two most important factors that influence human thermal comfort and could be addressed through planning and design in managing urban development. Wind, which Hong Kong is well endowed with, is particularly effective in mitigating the UHI effect. The key is to harness the wind potential through better planning and design to achieve thermal relief and reduction of heat stress, especially in the public realm A.4 Goal and Objectives The goal of this chapter is to attain urban thermal comfort by improving the urban climate in Hong Kong. To achieve the goal, appropriate planning and design measures at different School of Architecture, CUHK Page 468 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT spatial scales should be actively pursued, where opportunity arises, to achieve the following objectives: Reduce thermal load: To achieve localised cooling and reduce mean radiant temperatures within the built environment. Promote air ventilation: To optimise urban wind in dispersing urban heat and acilitating air exchange A.5 Scope and Application The following sections provide both government and private project proponents with a set of qualitative guidelines guiding land use planning, urban design, and planning and design of individual developments in early planning stages in order to realise a better urban climate and hence living environment. The qualitative guidelines in this chapter could be applied at two spatial scales, i.e. the district and project levels, which are interdependent and of equal importance. The aim is for individual projects to pursue progressive improvements in tandem with concurrent measures co-ordinated at the district level, thus resulting in area-wide improvement to the urban climate in the long-term. Concerted efforts from both the government and the private sector are necessary to improve the urban climate. Project proponents are encouraged to incorporate the planning and design measures into their projects as far as possible. Urban climate is one of many important considerations in the planning and design process. In applying the qualitative guidelines, other factors have to be considered side by side in order to strike a balance among different planning objectives. In particular, reference should be made to Chapter 11 of the HKPSG covering generic urban design guidelines and Chapter 4 on greening, which are both relevant to achieving a better living environment. In determining appropriate development parameters for individual sites, reference should also be made to relevant strategic and district planning contexts as well as individual site circumstances, including the development intensity as permitted under the Outline Zoning Plans (OZPs). School of Architecture, CUHK Page 469 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Section B: Urban Climatic Planning Recommendation Map The Urban Climatic Planning Recommendation Map (UC-ReMap) is an information and evaluation tool to integrate urban climatic factors and town planning considerations for a better urban climate. It is derived from the synthesis of key thermal load and dynamic potential variables under the Urban Climatic Analysis Map (UC-AnMap) with the input of wind information. Figure IV-2 Urban Climatic Planning Recommendation Map of Hong Kong The UC-ReMap has categorised Hong Kong into five Urban Climatic Planning Zones (UCPZs). The UCPZ categorisation is based on the understanding that the mean radiant temperature under shading in Hong Kong‘s summer is typically at 32 to 34oC, and that a 2oC decrease in mean radiant temperature is approximately equivalent to 1oC drop in PET. The UCPZs have been calibrated to reflect the PET classes and the necessary actions conducive to attaining the nPET for Hong Kong. Detailed methodology for the formulation of the UC- ReMap is at Appendix. Based on the UC-ReMap, urban climatically valuable or problematic areas in need of retention/ improvement could be identified at a district level to provide guidance in the School of Architecture, CUHK Page 470 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT preparation and review of OZPs. It also helps identify suitable locations for new development as well as evaluate broad urban climatic effects of major planning and development proposals. The UC-ReMap also identifies city climate areas with different ventilation system and key summer prevailing wind directions, channelling winds, sea breezes and downhill air movement areas, which provide an indication as to where potential breezeways, air paths and setbacks/non-building areas should be located and how they should be orientated and connected at the district planning level. The UC-ReMap is compiled from information from 100m by 100m grids with an assumption of homogeneity. When reading the map, the emphasis should be on the pattern and clusters/ areas of similar urban climatic characteristics at district level. A pixel-by-pixel scrutiny of particular individual developments/localities is not appropriate. Urban Climatic Planning Zones (UCPZs) There are five UCPZs on the UC-ReMap, for each UCPZ, broad strategic planning actions are recommended based on an understanding of the urban climatic characteristics of the area in relation to thermal load and dynamic potential, and the impact on human thermal comfort. UCPZ 1 covers mostly the natural vegetation areas at higher altitude with minimal obstructions to wind. As their cool air production capability is beneficial to adjoining urban areas, they need to be preserved as far as practicable. The majority of this zone is currently subject to different statutory controls such as country parks and conservation- related/ non- development zones on statutory town plans, and hence there is a presumption against development. Essential small-scale development is however possible subject to careful planning and design. UCPZ 2 covers areas which are currently urban climatically ―neutral‘ in terms of urban thermal comfort, and the general urban climatic characteristics should be maintained as far as possible. They mostly cover urban fringe areas or rural lowland. New low-density individual developments and comprehensive developments could be allowed subject to the incorporation of appropriate planning and building design measures as outlined in Section 7 of this chapter, to maintain the urban climatic condition. UCPZ 3 covers areas which are currently subject to urban climatically ―moderate‖ impact in terms of urban thermal comfort. They are mostly in the urban fringe or less dense development areas. Some mitigation actions are encouraged where possible. Additional School of Architecture, CUHK Page 471 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT development is permissible subject to satisfactory compliance with prudent planning and design measures. UCPZ 4 and UCPZ 5 are the densely built-up areas, including most of the new town areas and the metro areas at the northern part of Hong Kong Island, on Kowloon Peninsula and at Tsuen Wan. The existing developments have already had a strong to very strong impact on thermal comfort typified by high thermal load and low dynamic potential. Mitigation actions are essential and recommended. Intensification of use/additional development is not recommended unless with adequate mitigation measures. In brief, preservation of the climatically valuable areas is the focus for UCPZ 1. Opportunities to mitigate the high thermal load and low dynamic potential within UCPZs 3, 4 and 5 need to be maximised. With the emphasis on preservation in UCPZ 1 and on mitigation in UCPZs 3, 4 and 5, long-term development needs may be accommodated in UCPZ 2, in particular, on formed sites and spoiled rural areas, subject to prudent planning and building design measures. Section C: General Guidelines on Planning and Design Measures to Improve Urban Climate and Air Ventilation, Air Ventilation Assessment C.1 Planning and Design Measures to Improve Urban Climate and Air Ventilation In examining the urban climatic conditions for Hong Kong during the preparation of the UC- ReMap, a number of key factors affecting thermal load and dynamic potential have been identified. Accordingly, appropriate planning and design measures are devised to provide general guidance to tackle these factors in project planning stage. The planning and design measures can be implemented at district and project levels under the overarching objective to attain urban thermal comfort by reducing thermal load and promoting air ventilation. District Level (a) Greening Greening helps moderate the urban climate and ameliorate the effect of air stagnation by virtue of its cooling effect caused by evapotranspiration. In particular, from the School of Architecture, CUHK Page 472 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT urban climatic perspective, tree planting is the most beneficial and important form of greening for the following reasons: trees provide shading with their leafed tree crowns, which lower solar radiation intake at the ground surface; trees have lower surface temperatures, so less heat is reflected back to the ground surface; trees provide cool air spaces under their crowns, which enhance air movement and promote the dynamic potential of the ground surface; and trees act as pollutant filters for the street environment. Figure IV-3 Benefits of Tree Planting Other greenery such as grass and shrubs, though desirable, do not possess all the above benefits. Due to the tall building height in most urban developments, rooftop greening in the context of Hong Kong is less effective in promoting thermal comfort at the pedestrian level in the public realm. In promoting greenery, preference should therefore be for tree planting at grade. In view of its dual effect in reducing thermal load and promoting air ventilation, greenery should be preserved, maximised and promoted at the district level across all UCPZs, but especially within the urban areas. Clearance and covering of vegetated ground surfaces with impervious surface materials should be minimised as far as possible. School of Architecture, CUHK Page 473 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-4 Maximise Greenery in Urban Areas Greenery, particularly tree planting at grade, should be promoted/ maximised in open spaces, Government, Institution and Community (GIC) sites, open areas and alongside roads. Existing urban forest should be preserved and opportunities to create urban green oases should be maximised. A network of connected green corridors and green oases should be promoted, and preferably be within breezeways/air paths, to provide a more climatically pleasant pedestrian environment. Vegetated slopes can provide downhill cool air to adjoining urban areas. Vegetation on hill slopes should be safeguarded and, where feasible, be intensified through further tree planting to enhance the creation of cooler slope breezes. Where feasible, connected open spaces should extend from the hill slopes to urban areas to promote the penetration of downhill wind. For topographically enclosed or valley areas, green spaces should be provided at suitable locations to moderate the urban climate and promote air ventilation. (b) Proximity to Openness and Connectivity Breezeways and air paths facilitate air ventilation for urban areas, which in turn moderates the urban climate. Major breezeways should be aligned primarily along major prevailing wind directions and, as far as possible, be positioned perpendicular to waterfronts and vegetated hill slopes, in order to channel sea/ downhill breezes and valley winds to the built-up area. To enhance their effectiveness, air paths intersecting the breezeways should also be provided, preferably at right angles or at an angle to one another, and be extended over a sufficiently long distance for continuity. Greening should be provided along breezeways and air paths in order to promote cooler and cleaner air movements. School of Architecture, CUHK Page 474 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-5 Breezeways and Air Paths Breezeways should be created by connecting major open ways, such as principal roads, water channels, inter-linked open spaces, amenity areas, non-building areas and/or building setbacks. Minor roads should be widened and connected to major roads as far as practicable to form a network of ventilation corridors/ air paths to promote permeability and hence air ventilation in urbanised areas. Although less effective than open ways, breezeways may also be formed over areas of low ground roughness, such as along low-rise building corridors and non-building areas at podium level, where no better alternatives are available. Any recognised breezeways and air paths over existing low-rise, low-density GIC sites should be preserved as far as possible. Figure IV-6 Linkage of Roads, Open Spaces and Low-rise Buildings to Form Breezeways School of Architecture, CUHK Page 475 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (c) Building Volume Large building volumes have an effect on thermal load due to its localised heat carrying capacity and its cumulative contribution to a lower Sky View Factor, which reduces the nighttime radiative cooling effect in cities. As a general principle, the development intensity within UCPZs 3, 4 and 5 should not be further intensified, unless with prudent planning and design measures incorporated as mitigation measures. However, in determining the building volume of individual sites, consideration must also be given to site circumstances. Buildings with the same gross floor area may have different building volumes and thus thermal load, due to different floor-to-floor heights. Excessive floor-to-floor height should be avoided. (d) Permeability of the Urban Fabric Site Geometry and Disposition Sites should be divided into parcels to avoid long and linear site geometry which could likely result in single-aspect and ―wall-like‖ development not conducive to air ventilation. Street Orientation, Pattern and Widening An array of main streets/wide avenues should be aligned in parallel, or up to 30 degrees to the prevailing wind direction, in order to maximise the penetration of prevailing wind through the district. Figure IV-7 Orientation of Street Grids School of Architecture, CUHK Page 476 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT The length of street grid perpendicular to the prevailing wind direction should be as short as possible with a view to minimising stagnant zones while maximising breezeways across the urban area. Figure IV-8 Pattern of Street Grids To improve air ventilation in the urban areas, street widening along the prevailing wind direction is highly effective. For large sites facing narrow urban canyon as typically found in old and congested urban districts like Mong Kok, building setback on both sides of the street should be provided upon development or redevelopment. Figure IV-9 Street Widening/Building Setback Land parcels should be laid out and orientated to maximise air penetration by aligning the longer frontages parallel to the prevailing wind direction and by introducing non- building areas and setbacks where appropriate. School of Architecture, CUHK Page 477 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Waterfront Sites The extensive coastline of Hong Kong and riverfronts in some new town development areas are of strategic importance in allowing sea breezes into the urban hinterland due to the sea cooling effect. Special considerations should be given to the appropriate scale, height and disposition of building blocks along the waterfront to avoid blockage of sea/ land breezes and prevailing winds. Figure IV-10 Waterfront Buildings Should Avoid Wind Blockage Where appropriate, non-building areas should be designated perpendicular to the waterfront to channel sea breezes inland. The waterfront should be connected with the vegetated hilly backdrops through breezeways, air paths, open spaces, green oases, landscaped pedestrian ways, and low-rise buildings etc., to enhance air ventilation. Figure IV-11 Connecting the Waterfront with Vegetated Hill Backdrops School of Architecture, CUHK Page 478 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-12 Promoting Wind Connectivity (e) Building Height Profile A varying height profile with strategic disposition of low-rise and tall buildings in the dense urban context can enhance air ventilation throughout the district. Certainly, this has to be balanced with visual considerations. In general, gradation of building heights would help wind deflection and avoid air stagnation. Where appropriate, height variation across the district with decreasing heights towards the direction where the prevailing wind comes from should be adopted to promote air movements. Figure IV-13 Varying Height Profile to Promote Air Movements Low-rise buildings and open spaces should be located in the windward direction and waterfront areas, and scattered within high-density neighbourhoods to create breathing spaces and building height variation. Low-rise buildings and open spaces within breezeways/ air paths should be maintained. The intensification of GIC uses, which have been serving as breathing spaces in the existing environment, should be avoided. School of Architecture, CUHK Page 479 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-14 Breathing Spaces within the Neighbourhood In low/medium density areas with building height-to-street width (H/W) ratio of two or below, controlling building heights is effective in promoting air ventilation. However, in medium/high density areas with a higher H/W ratio of three or above, building height control alone may not be effective; other parallel measures to encourage lateral wind flow, such as building separations, air paths, building setbacks, greenery and reducing ground coverage, etc. would be needed. Tall and elongated buildings forming a ―wall-like‖ structure to the windward direction of the prevailing wind or along the waterfront should be avoided. Tall buildings within a neighbourhood should be distributed in such a way as not to cause adverse impact on wind penetration. Project Level (a) Greening For individual developments, the land area and variety of greenery should be maximised in open spaces and open areas, supplemented with green podiums, green walls and green roofs. To maximise pedestrian comfort, tall trees with wide and dense canopies should be planted at grade in entrance plazas, building setback areas and major pedestrian ways. Landscaping should also be used to segregate major pedestrian areas from the exhaust and other nuisances arising from major roads, public transport interchanges and refuse collection points, etc. School of Architecture, CUHK Page 480 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-15 Tall Trees with Wide and Dense Canopy in Plaza To strike a balance between practicality considerations with the effectiveness of cooling at ground level, individual developments should, in general, aim to achieve 20 - 30% greening, preferably through tree planting at grade. (b) Ground Coverage41 Smaller ground coverages are conducive to promoting air ventilation in the public realm and should be encouraged. Compact integrated developments and podium structures with full or large ground coverage on extensive sites are particularly impeding on air movement in the dense urban fabric and should be avoided. The following measures should be applied at the street level for large development/ redevelopment sites, particularly in the existing urban areas: provide setbacks along narrow streets and parallel to the prevailing wind direction; Figure IV-16 Encourage Setbacks along Narrow Streets 41 Ground coverage measures the actual physical ground areas occupied by building structures. The ground coverage ratio is an indicator of urban permeability. School of Architecture, CUHK Page 481 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT designate non-building areas to sub-divide large land parcels; reduce frontage area of buildings facing the prevailing wind; and/or reduce site coverage of the podia to allow more open space at grade. Figure IV-17 Reducing Site Coverage of the Podia to Allow More Open Space at Grade Where podium is unavoidable, a terraced podium design should be adopted to direct downward airflow to the pedestrian level. Podium should be as permeable as possible for better air ventilation. Figure IV-18 Terraced Podium Design (c) Building Permeability Building Separation Closely-packed buildings and buildings with long frontages tend to impede airflow. The provision of appropriate building gaps/separations can help facilitate air School of Architecture, CUHK Page 482 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT movement. Making reference to the Building Department‘s Practice Note for Authorised Persons, Registered Structural Engineers and Registered Geotechnical Engineer (PNAP) APP-152 ‗Sustainable Building Design Guidelines‘, building separations that provide a permeability equivalent to 20% to 33.3% of the total projected facades of the buildings is a good starting point in promoting air ventilation. For prominent sites, especially those next to the waterfront or open areas, greater permeability should be targeted. Figure IV-19 Building Permeability and Building Separation Building Gap The provision for higher permeability of building masses can be achieved by creating gaps between building blocks, between the podium and the building blocks built atop (i.e. a void podium deck) and within building blocks at various levels. In general, permeability near the ground level can be of greater benefit to the pedestrian level, which should be encouraged. Figure IV-20 Gaps Between the Podium and Building Blocks to Enhance Air Permeability Building Disposition Suitable disposition of building blocks could facilitate effective airflows around buildings in desirable directions. Where practicable, adequately wide gaps should be provided between building blocks to maximise the air permeability of the development and minimise its impact on wind capturing potential of adjacent developments. For large development sites, this may be achieved through the designation of appropriate air paths, non-building areas and building separation. School of Architecture, CUHK Page 483 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-21 Disposition of Non-building Areas to Create Air Paths The non-building areas/ building gaps for enhancing air permeability should be positioned perpendicular to the prevailing wind direction. Figure IV-22 Building Gaps to Enhance Air Permeability To minimise obstruction of airflow, the axis of the building blocks should be parallel to the prevailing wind. To allow individual building blocks to capture more wind for better indoor natural ventilation, the angle between the axis of the building blocks and the prevailing wind direction should be within 30 degrees. The arrangement of the building blocks should be staggered to enable the blocks behind to receive the wind penetrating through the gaps between the blocks in the front row. Where appropriate, towers should abut the podium edge that faces the main pedestrian area/street perpendicular to the wind direction so as to enable most of the downwash wind to reach the street level. School of Architecture, CUHK Page 484 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-23 Disposition of Towers to Facilitate Downwash (d) Projecting Obstructions Projecting Obstruction Projecting obstructions over breezeways/air paths should be avoided to minimise wind blockage. Massive elevated road structures aligned by tall buildings or traversing street canyons, which could create air stagnant spaces below, should be avoided. Projecting signboards should be aligned vertically instead of horizontally, especially in areas with high pedestrian activities. Figure IV-24 Projecting Signboards should be Aligned Vertically instead of Horizontally (d) Building Height Stepping building height concept can help optimise the wind capturing potential of individual developments. Figure IV-25 Stepping Height Profile to Divert Winds to Lower Levels School of Architecture, CUHK Page 485 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Built forms that would generate a small eddy area to allow a maximum of cooling air to flow around and through building structures should be considered. (e) Cool Materials Cool materials, which are characterised by high solar reflectivity and/or high emissivity, should be used in the construction of pavements, streets and building façades to decrease absorption of solar radiation and urban radiant temperature. For streets, the use of asphalt with a high percentage of white aggregates should be considered. Cool sinks, such as trees and water bodies, should also be provided, where appropriate. C.2 Air Ventilation Assessment To aid planning and design for better air ventilation through the city fabric, AVA has to be conducted for public and private developments that may have potential air ventilation impacts, including, but not limited to: District Level (a) Planning studies for new development areas; (b) Comprehensive land use restructuring schemes, including schemes that involve amalgamation of sites together with closure and building over of existing streets; (c) Area-wide plot ratio and height control reviews; Site Level (d) Developments on sites of over 2 hectares and with an overall plot ratio of 5 or above; (e) Development proposals with total Gross Floor Area exceeding 100,000 square metres; (f) Developments with podium coverage extending over one hectare; (g) Developments above public transport terminus; (h) Buildings with height exceeding 15 metres within a public open space or breezeway designated on layout plans/ outline development plans/ OZPs or proposed by planning studies; (i) Developments on waterfront sites with lot frontage exceeding 100 metres in length or non-waterfront sites with lot frontage exceeding 140 metres in length; or (j) Extensive elevated structures of at least 3.5 metres in wide, which abut or partially cover a pedestrian corridor along the entire length of street block that School of Architecture, CUHK Page 486 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT has/ allows development at plot ratio 5 or above on both sides; or which covers 30% of a public open space. AVA could help establish the acceptability of a development in air ventilation terms by checking against the Wind Performance Criterion, comparing air ventilation impacts of design options and to identify potential problem areas and mitigation measures for design improvement. For developments requiring AVA, the following Wind Performance Criterion, which comprises two components, shall be applicable: The Hong Kong Wind Performance Criterion has two components: (A) Wind Performance Requirement (a) 80% of all test points inside the assessment area as defined in the AVA Technical Circular have: Annual median hourly mean wind speed ＞＝ 1 metre/second (m/s) Summer median hourly mean wind speed ＞＝ 1 m/s AND (b) 95% of all test points inside the assessment area as defined in the AVA Technical Circular have: Annual median hourly mean wind speed ＞＝ 0.6 m/s Summer median hourly mean wind speed ＞＝ 0.6 m/s (B) Alternative (Prescriptive) Approach The Wind Performance Requirement above, especially in the summer months, may be difficult to achieve in some areas of Hong Kong, due to the existing topography and compact building morphology, such as high density, narrow streets, large buildings bulk, large podia and limited site wind available in the surroundings. Subject to demonstration that the Wind Performance Requirement, after all the possible and practical mitigation measures have been considered and incorporated where appropriate, cannot be practically achieved, the project proponent may be allowed to incorporate the following four mitigating design measures into the development proposal, as an alternative to meet the wind performance requirement: (a) building permeability requirement for the middle and high assessment zones to follow PNAP APP-152, including: School of Architecture, CUHK Page 487 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT • 20% to 33% (subject to site area and height of the tallest building) on two projected planes for the middle and high assessment zones • the ―continuous projected façade length― (Lp) of any building or groups of building that abuts a street should not exceed the maximum Lp (b) ground coverage: • not more than 65% (open areas preferably along narrow streets (circa. 15m wide) and public areas heavily patronised by pedestrians) • sites smaller than 1,000 square metres exempted (c) set back: no part of the building, up to a level of 15m above the street level, shall be within 7.5m from the centreline of the streets as per building set back requirement near narrow street as per PNAP APP-152 (d) green coverage: sites larger than 1 hectare shall provide 30% green coverage with at least half of which at grade sites of 1,000 square metres to 1 hectare shall provide 20% green coverage, preferably tree planting, with at least one half of which at grade sites smaller than 1,000 square metres are exempted A quantitative AVA shall be carried out to demonstrate that the design option with the four measures above to optimize the air ventilation performance has been selected in comparing with different design options. Incorporation of the above mitigating design measures could help avoid adding adverse impact on the existing urban climate at individual development site. Through the Alternative (Prescriptive) Approach, the combined effects of developments on each site will result in a higher chance to ultimately achieve the wind performance requirement in Hong Kong. Exemption Developments with demonstrated functional requirements in terms of building length and / or ground coverage (e.g. infrastructural facilities, transport terminus, sports and civic facilities) may be exempted from the mitigating design measures under the Alternative (Prescriptive) Approach, provided that the following are undertaken: School of Architecture, CUHK Page 488 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT building separation requirement is fully complied with for other buildings on the same site or other parts of the building that are located above such special facilities being exempted, where applicable; a quantitative AVA be conducted to demonstrate that the design option with all practicable mitigation / improvement measures has been selected in comparing with different design options; and maximising greening and tree planting opportunities within the pedestrian zone, preferably at grade and at the part of the site not built over. The technical framework for conducting AVAs has been set out under the revised Technical Circular No. xx/12 on AVA (with the detailed methodology set out in the Technical Guide on AVA as an attachment), issued by the Development Bureau in xxxx 2012. For details on the AVA technical requirements and methodology, including the Wind Performance Criterion, reference can be made to the Technical Circular. Section D: Conclusion The qualitative planning and design guidelines established in this chapter are conducive to improving the urban climate and air ventilation in the planning and design process. The measures would not be implemented all at once or uniformly throughout the city. However, with the concerted efforts of the public and private sectors, the urban climatic condition and quality of the living environment in Hong Kong would gradually improve for the better, to the benefit of our future generations. Appendix: Methodology for Urban Climatic Planning Recommendation Map Urban Climatic Analysis Map The urban climatic maps consist of two elements, the Urban Climatic Analysis Map (UC-AnMap) and the Urban Climatic Planning Recommendation Map (UC-ReMap). The formulation of the UC-AnMap for Hong Kong has taken into account international experiences, including references to the Federal German Standard VDI- 3787-Part1: Environmental Meteorology Climate and Air Pollution Maps for Cities and Regions, the Thermal Environmental Map studies of Japan and the unique climatic characteristics and urban morphologies of Hong Kong. The full sequence for the formulation of the urban climatic map is summarised below. School of Architecture, CUHK Page 489 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-26 Methodology of Formulating Urban Climatic Maps On the outset, the urban climate of the city is analysed based on a balanced consideration of Thermal Load and Dynamic Potential effects. Thermal Load Analysis focuses on the important variables contributing to the localised thermal loads. A major negative factor which will increase thermal load is building volume, whilst topography and green space are positive factors contributing to a reduced thermal load. Dynamic Potential Analysis focuses on the important variables (ground roughness) affecting the wind environment. A major negative factor which will decrease air ventilation is ground coverage, whilst natural landscape and proximity to openness are the main positive factors contributing to increased air movement. School of Architecture, CUHK Page 490 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-27 Urban Climatic Factors for Thermal Load and Dynamic Potential Analysis Urban climatic and geometric data with respect to the six thermal load and dynamic potential related factors are assembled. Physiological Equivalent Temperature (PET), as a human urban thermal comfort indicator, is used to synergise and analyse all six factors according to their relationship and effects on wind and thermal comfort. Positive and negative classification values are assigned corresponding to gain or loss in thermal load and/or dynamic potential resulting from varying scales of each parameter. The resultant value denotes the net effect of the parameters on the urban climate. School of Architecture, CUHK Page 491 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Figure IV-28 Human Heat Balance Model Based on thorough analysis and evaluation of the associated factors, the urban climatic factors are translated into eight different climatopes / classes in the form of the UC-AnMap. The UC-AnMap is developed to capture the most critical conditions in Hong Kong, i.e. the hot and humid summer months of June, July and August. Figure IV-29 Urban Climatic Analysis Map for Hong Kong The UCM Study established, through the Users‘ Thermal Comfort Survey, that the nPET in Hong Kong during the summer month is 28oC. A 2oC decrease in mean radiant temperature was found to be approximately equivalent to 1oC drop in PET. With considerations for the mean radiant temperature under shading in Hong Kong during the summer, which is typically at 32 to 34oC, the PET classes can be used to interpret the degree of mitigation needed to remedy the urban climatically problematic areas in parts of Hong Kong. The general existing thermal load and dynamic potential conditions with each of the urban climatic classes of the UC-AnMap are summarised below: Class 1 are areas with moderately negative thermal load and good dynamic potentials, situated on the higher altitudes of mountains and steep vegetated slopes. Adiabatic cooling and trans-evaporative cooling are prevalent, as a result, the temperature is usually very cool. These areas are also sources of cool downhill wind. This urban School of Architecture, CUHK Page 492 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT climatic class includes the summits of various mountains and peaks, e.g. Victoria Peak, peaks at Kowloon, Tai Mo Shan, Pat Sin Leng, and Lantau Peak etc. Class 2 are areas with slightly negative thermal load and good dynamic potentials. These areas are extensively covered by natural vegetation, greenery and natural coastal areas. Evapotranspiration cooling is prevalent, and as a result, the temperature is generally cooler. These areas act as sources of cool and fresh air. They include many of the country park areas, beaches and outlying islands, e.g. Plover Cove, Clear Water Bay and Po Toi etc. Class 3 are areas with low thermal load and good dynamic potentials, which usually consist of more spaced out developments with smaller ground coverage, and open spaces near the sea. As a result, the temperature is mild. This urban climatic class includes some undeveloped coastal areas and many low-density developments in the urban fringe areas or suburban outskirts, e.g. South West Kowloon headland, Kai Tak, Mui Wo, Shek O, and Tseung Kwan O South, and Pak Shek Kok Science Park etc. Class 4 are areas with some thermal load and some dynamic potentials, which usually consist of areas with low to medium building volumes in a developed yet more open setting, such as the sloping areas with a number of open spaces between buildings. As a result, the temperature is slightly mild. This urban climatic class includes the Mid- levels, Upper Happy Valley, Chinese University of Hong Kong and other hillside development areas etc. Class 5 are areas with moderate thermal load and some dynamic potentials, which usually consist of areas with medium building volumes in low-lying areas further inland from the sea or in areas fairly sheltered by natural topography. As a result, the temperature is warm. This urban climatic class includes many medium- density developed urban areas with greenery, such as Discovery Bay, Fairview Park and Hon Lok Yuen etc. Class 6 are areas with moderately high thermal load and low dynamic potentials, which usually consist of areas with medium to high building volumes located in low- lying, developed areas with relatively less urban greenery. As a result, the temperature is very warm. This urban climatic class includes peripheral parts of the main urban area and many of the development areas in new towns. Class 7 are areas with high thermal load and low dynamic potentials, which usually consist of areas with high building volumes located in low-lying, well-developed areas with little open space. As a result, the temperature is generally hot. This urban climatic class includes most of the developed parts of the main urban areas in Kowloon, the north shore of Hong Kong Island and core development areas of new towns. Class 8 are areas with very high thermal load and low dynamic potentials, which usually consist of areas with very high and compact building volumes with very limited open spaces and permeability due to shielding by buildings on many sides. School of Architecture, CUHK Page 493 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Full and large ground coverage is prevalent and air paths are restricted from the nearby seas or hills. As a result, the temperature is very hot. This urban climatic class includes some highly developed core areas, such as Tsim Sha Tsui, Yau Ma Tei, Mong Kok, Lai Chi Kok, Sheung Wan, Central, Wan Chai, Causeway Bay and North Point. Wind Information Layer To supplement the UC-AnMap, a set of important wind data for the summer months (June to August) were deduced primarily from long term wind data of 40 Hong Kong Observatory stations around Hong Kong, and supplemented with the Hong Kong University of Science and Technology‘s MM5/CALMET 2004 model for wind simulations at 60m above ground level, with considerations for topography, greenery and ground roughness. The information was expertly evaluated and the background wind, including any channelling effects due to topography, the localised land and sea breezes, and the downhill air movements are noted. Areas of similar wind characteristics are also grouped into zones under the Wind Information Layer. Figure IV-30 Wind Information Layer for Hong Kong School of Architecture, CUHK Page 494 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT Urban Climatic Planning Recommendation Map For clear and definable planning actions, the eight urban climatic classes of the UC- AnMap are consolidated into five Urban Climatic Planning Zones (UCPZ) in accordance with their similar urban climatic characteristics with reference to human thermal comfort and planning implications. Figure IV-31 Categorisation of Urban Climatic Classes into Urban Climatic Planning Zones In line with international practice, the Wind Information Layer is then superimposed to formulate the Urban Climatic Planning Recommendation Map (UC-ReMap) Urban Climatic Planning Zones Based on the five UCPZs of the UC-ReMap, specific recommendations on the strategic planning actions can be made, which gives planners a reference when balancing urban climate with other planning considerations. UCPZ 1 comprises areas extensively covered with natural vegetation, at higher altitude and with fewer obstructions to wind. They provide a cooler and more conducive thermal comfort environment, and their cool air production capability can be beneficial to nearby urban areas. Their urban climatic conditions should be preserved. The broad strategic planning actions recommended are: School of Architecture, CUHK Page 495 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (a) Natural areas especially sources of cold air production and drainage areas beneficial to other areas (e.g. vegetated hill slopes adjacent to urban areas) should be preserved. Sealing (covering of ground surface) or development should be discouraged. (b) In view of its urban climatic value, there is a general presumption against major development in this zone. (c) Small-scale and essential development may be allowed in areas other than in natural areas identified in 1 above subject to: (i) careful planning and design of these developments to minimise any disruption to the existing urban climatic characteristics; (ii) maximising greenery and open areas; and (iii) minimising sealing (covering of ground surface). UCPZ 2 comprises, at present, urban climatically ―neutral‖ areas in terms of urban thermal comfort. They are mostly urban fringe or rural lowland. It is important to maintain their urban climatic characteristics. The broad strategic planning actions recommended are: (a) General urban climatic characteristics such as lower building volume, open spaces and greenery should be maintained as far as possible. (b) New low-density individual developments could be allowed subject to: (i) a low building volume and a satisfactory disposition of buildings to align with the prevailing wind directions and preserve existing air paths; (ii) a low ground coverage in order not to impede air flow; and (iii) maximisation of greenery within development sites. (c) New comprehensive development is possible subject to thorough urban climatic consideration. Prudent planning and building design is necessary to avoid degrading the urban climatic condition. Breezeways and air paths must be carefully designed. Street grids and building disposition must respect prevailing wind directions. High building volume and ground coverage should be discouraged. UCPZ 3 covers areas currently subject to urban climatically ―moderate‖ impact in terms of thermal comfort. Some mitigation actions are encouraged where possible. They are mostly in the urban fringe or less dense development areas. The broad strategic planning actions recommended are: (a) Additional development is permissible subject to: School of Architecture, CUHK Page 496 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT (i) urban climatic evaluation in terms of building volume and green coverage; (ii) dispositioning of new buildings in line with the prevailing wind directions, to preserve/enhance existing air paths; (iii) reduction of ground coverage in order not to impede air movement; and (iv) maximisation of greening, particularly tree planting within development sites and adjoining streets. (b) Greening should be promoted in open areas as far as practicable. UCPZ 4 covers areas already densely built up. Thermal Load is high and Dynamic Potential is low. Some strong impact on thermal comfort is expected. Mitigation actions are recommended and necessary. Isolated clusters of UCPZ 4 can be found in the new towns in Tai Po, Ma On Shan, Yuen Long, Tin Shui Wai and Tung Chung, etc. These areas currently benefit from the surrounding extensive green areas (UCPZs 1 and 2), downhill air movements and valley winds. These green areas and natural ventilation systems should be preserved. Other clusters of UCPZ 4, mixed with scattered UCPZ 5, can be found in Tseung Kwan O, Tuen Mun, Shatin and Aberdeen, etc. There are air paths and breezeways dividing the development clusters within these areas, which provide useful air ventilation reliefs. The broad strategic planning actions recommended are: (a) Air paths/breezeways, and low-rise, low-density ‗Government, Institution or Community‘ (GIC) sites should be preserved as far as possible; (b) Greenery, particularly tree planting on streets and open areas, should be increased; (c) Additional development should not be allowed unless with appropriate mitigation measures, including: (i) reducing ground coverage to balance against any increase in building volume; (ii) respecting existing air paths and introducing new ones, if feasible; (iii) positioning buildings to align with the prevailing wind directions; and (iv) maximising greening within development sites. UCPZ 5 comprises very densely built-up areas. Thermal Load is very high and Dynamic Potential is low. Very strong impact on thermal comfort is expected. A high frequency of occurrence of thermal stress is anticipated. Mitigation actions are recommended and essential. UCPZ 5, intermixed with UCPZ 4, are found in the metro areas of Hong Kong at the northern part of the Hong Kong Island, at the Kowloon Peninsula and at Tsuen Wan. The broad strategic planning actions recommended are: (a) Intensification of GIC sites, which serve as a relief to the existing condition, should be avoided. Additional and intensified greening within the GIC sites is School of Architecture, CUHK Page 497 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT essential; (b) Additional greenery and tree planting on open areas and streets in this zone is essential and recommended. Intensified greening in ―Open Space‖ zones is strongly recommended; (c) The existing urban environment should be improved by: (i) identifying, respecting, widening and enhancing existing air paths; (ii) creating new air paths; (iii) reducing ground coverage, setting back building line along narrow streets, aligning the long frontage of building with prevailing wind directions; and (iv) maximizing on-site greening upon development /redevelopment; (d) Intensification of use, adding building volume and/or ground coverage are not recommended unless with strong justifications and appropriate mitigation measures. School of Architecture, CUHK Page 498 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT APPENDIX 5: WIND PROFILE School of Architecture, CUHK Page 499 of 518 Planning Department: Urban Climatic Map and Standards for Wind Environment – Feasibility Study FINAL REPORT REFERENCES (2005) The thermal environment map and areas designated for the implementation of measures against the Heat Island Phenomenon. Tokyo, Japan, Bureau of Environment, Bureau of Urban Development, Tokyo Metropolitan Government. Ahmed, K. S., (2003): Comfort in urban spaces: defining the boundaries of outdoor thermal comfort for the tropical urban environments. Energy and Buildings. 35, 103-110. Architectural Institute of Japan (AIJ). 2008. National Research Project on Kaze-no-michi: Making the Best Use of the Cool Sea Breeze. Newsletter on Urban Heat Island Countermeasures, Vol. 4 Architectural Institute of Japan(AIJ). 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