sustainability

Article Urban Heat Island and Overheating Characteristics in Sydney, Australia. An Analysis of Multiyear Measurements

Mat Santamouris 1,*, Shamila Haddad 1, Francesco Fiorito 1, Paul Osmond 1, Lan Ding 1, Deo Prasad 1, Xiaoqiang Zhai 2 and Ruzhu Wang 2

1 Annita Lawrence Chair of High Performance Architecture, Faculty of Built Environment, University of New South Wales, Sydney 2052, Australia; [email protected] (S.H.); f.fi[email protected] (F.F.); [email protected] (P.O.); [email protected] (L.D.); [email protected] (D.P.) 2 Institute of Refrigeration and Cryogenics, Shanghai Jiao Tong University, Shanghai 200240, China; [email protected] (X.Z.); [email protected] (R.W.) * Correspondence: [email protected]; Tel.: +61-293-850-729

Academic Editors: Constantinos Cartalis and Marc A. Rosen Received: 4 February 2017; Accepted: 25 April 2017; Published: 29 April 2017

Abstract: It has become increasingly important to study the urban heat island phenomenon due to the adverse effects on summertime cooling energy demand, air and water quality and most importantly, heat-related illness and mortality. The present article analyses the magnitude and the characteristics of the urban heat island in Sydney, Australia. Climatic data from six meteorological stations distributed around the greater Sydney region and covering a period of 10 years are used. It is found that both strong urban heat island (UHI) and oasis phenomena are developed. The average maximum magnitude of the phenomena may exceed 6 K. The intensity and the characteristics of the phenomena are strongly influenced by the synoptic weather conditions and in particular the development of the sea breeze and the westerly winds from the desert area. The magnitude of the urban heat island varies between 0 and 11◦C, as a function of the prevailing weather conditions. The urban heat island mainly develops during the warm summer season while the oasis phenomenon is stronger during the winter and intermediate seasons. Using data from an extended network of stations the distribution of Cooling Degree Days in the greater Sydney area is calculated. It is found that because of the intense development of the UHI, Cooling Degree Days in Western Sydney are about three times higher than in the Eastern coastal zone. The present study will help us to better design and implement urban mitigation strategies to counterbalance the impact of the urban heat island in the city.

Keywords: urban heat island; coastal cities; Sydney; Australia

1. Introduction The Urban Heat Island (UHI) is the most documented phenomenon of climate change. According to recent studies, the presence of UHI is recognized in more than 400 cities around the world [1,2], The UHI refers to a higher ambient temperatures in dense urban zones compared to the surrounding suburban or rural areas. The development of the UHI is influenced by the synoptic weather conditions in the area, the local morphological and structural parameters of the city, the thermal quality of the materials used, the magnitude of the anthropogenic heat released, and the presence of heat sources and sinks in the cities [3]. The urban heat island considerably increases the peak electricity demand and the cooling energy consumption of buildings, deteriorates the levels of outdoor and indoor comfort,

Sustainability 2017, 9, 712; doi:10.3390/su9050712 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 712 2 of 21 raises the concentration of several harmful pollutants, seriously affects human health and increases the risk levels for vulnerable populations [4]. Recent research has shown that because of the urban heat island, the peak electricity demand increases between 0.45% and 4.6% per degree of temperature rise [5]. In parallel, it is reported that the average cooling energy penalty induced by the urban heat island is close to 68 kWh/p/K, or 0.8 kWh/m2/K [6]. Studies carried out in different cities have also shown that UHI may increase the cooling demand of buildings up to 100% [7,8]. The very important increase of the cooling demand induced by the urban heat island in combination with other drivers, like population increase and the rapid penetration of air conditioning devices, may increase the global cooling needs of the residential and commercial sectors up to 750% and 275%, respectively, by 2050 [9]. Furthermore, the UHI affects meteorological conditions, e.g. impacting the atmospheric boundary layer (ABL) depth in urban areas, in particular during the nighttime [10]. Besides the important energy problem induced by UHI, the impact on the thermal comfort, health and vulnerability of urban citizens should not be underestimated. Several studies have reported a serious reduction in outdoor comfort levels because of this phenomenon [11]. In parallel, large-scale measurements of the indoor environmental conditions in low-income houses during the hot summer period have shown that indoor temperatures largely exceeded the threshold temperatures for health [12]. The effects of UHI related to human health and wellbeing have been highlighted in the literature [13,14]. Finally, recent research has demonstrated a strong correlation between increased urban temperatures and human mortality [15]. Coastal cities suffer from the urban heat island despite the development and positive impact of the sea breeze [16]. Several experimental and numerical investigations have shown the impact of the sea on the development of the UHI in coastal cities [17–24]. Most of the investigations agree that although the UHI despite under the presence of the sea breeze, the intensity of the phenomenon in coastal areas is reduced because of the important transfer of relatively cool air into the city [25–30]. The specific interaction of the urban heat island and the sea breeze has been studied through numerical and experimental investigations. Several numerical studies have concluded that the UHI delays the flow of the sea breeze because of the creation of a stagnation region over the city [17,19,29]. This results in a higher cooling impact in coastal than in inland urban zones, while the cooling potential of the sea breeze is considerably reduced with an increase in the distance from the coastal areas. Other studies have concluded that the presence of the urban heat island accelerates the flow of the sea breeze towards the city and the speed of the sea breeze increases significantly compared to the case where no city exists [21,23]. The present paper investigates the magnitude and the characteristics of the UHI in a coastal city, Sydney, Australia. Ten years of climatic data from six stations, distributed in the greater Sydney area, are used. The objective of the work was to determine in depth the magnitude and the characteristics of the problem in order to propose specific mitigation and adaptation measures to counterbalance the impact of overheating in the city. This is the first time that the characteristics and magnitude of the urban heat island have been studied and reported for Sydney. The information provided will help to inform mitigation strategies to counteract the phenomenon. Also, the study provides important information on the thermal conditions of coastal zones influenced by the advection of warm air from inland. This is a rather rare climatological case and the present article is among the first to study and report it.

2. Sydney’s Geographical Location and Population Sydney is located on the southeast coast of Australia at 33.8◦S latitude, bordering the Tasman Sea to the east. Metropolitan Sydney is classified as Greater Sydney, the Capital City Statistical Division, by the Australian Bureau of Statistics (ABS). Greater Sydney is the capital of the state of New South Wales (NSW). It is the largest city in Australia, covers a land area of approximately 12,367.7 km2 and is made up of 43 local councils (This number has been reduced to 30 following council amalgamations since Sustainability 2017, 9, 712 3 of 21 this research was conducted. Hence mention of council land areas, populations, etc. below refer to the pre-amalgamation situation). The area follows the coastline from Gosford in the north to the Royal National Park in the south. The region includes Parr State Conservation Area and the Blue Mountains to the west. The Sydney metropolitan area lies within the flat Cumberland Basin to the south and west of Port Jackson, and is surrounded by the Hornsby and Blue Mountains Plateaus and steep escarpments to the north and west, with elevations of up to 300 and 600 m above sea level, respectively. According to the Australian Statistical Geography Standard [31], the Sydney urban area extends 70 km from the coastline in the east to the Blue Mountains in the west. Greater Sydney is the most populous city in Australia, with a population of approximately 4.92 million people in June 2015 [32]. Based on the land area, the current population density of metropolitan Sydney is 397.8 persons per square kilometre.

3. Climate of Sydney Sydney has a humid subtropical climate [33] and is characterised by warm summers and cool winters. It features a Cfa climate based on the Köppen–Geiger climate classification [34]. The annual monthly mean temperature recorded at Observatory Hill in the central business district (CBD) ranged from 13.8 ◦C to 21.7 ◦C based on long-term monthly average data from 1859 to 2016 [35]. The mean daily maximum and minimum temperatures on vary between 25.9 ◦C in the summer (January) and 8.1 ◦C in the winter (July). January is the warmest month, with an average daily air temperature of 18.7 ◦C to 25.9 ◦C, and the highest recorded maximum temperature of 45.8 ◦C. Based on long-term climate data [35], the temperature exceeds 30 ◦C for an average of 14.9 days a year. In contrast, winters are cool, with temperatures dropping below 10 ◦C from June to August. The annual monthly mean temperature recorded at Observatory Hill in July varied from 8.1 ◦C to 16.4 ◦C, with the lowest recorded minimum temperature of 2.2 ◦C[35]. The annual average temperature in Western Sydney, at Prospect Reservoir, varied from 12.2 ◦C to 23.2 ◦C based on long-term averages over the past 51 years, with the average daily maximum and minimum temperatures of 6.1–28.4 ◦C. The temperature falls above 30 ◦C for an average of 45.5 days a year, which is almost three times higher than that in Sydney CBD [35]. The highest and lowest temperatures on record are 45.1 ◦C and −0.8 ◦C, respectively. The mean daily maximum temperature in Penrith, located approximately 50 km west of Sydney CBD, reaches up to 30.7 ◦C with a highest temperature of 46.5 ◦C on record [35]. The annual average daily maximum and minimum temperatures varied from 12.4 ◦C to 24.5 ◦C. The coldest month in Penrith is July, with an average range of 5.5 ◦C–17.7 ◦C, and a lowest temperature of −1.4 ◦C. Penrith has an average of 68.6 days a year with a daily maximum of more than 30 ◦C and 19.3 days a year over 35 ◦C[35]. Rainfall is uniform and occurs throughout the year with an annual rainfall of approximately 1000–1500 mm [35]. The climate of Greater Sydney is significantly affected by its coastal position and the proximity to the ocean. This is clearly suggested by the increase in the mean and maximum summer temperatures from the coastal zone near the CBD towards the inland Western suburbs by 2–5 ◦C. This, however, depends on the wind speed and direction.

4. Description of the Meteorological Stations and Data The half hourly climate data (dry bulb temperature, wind speed and wind direction, dew point temperature, humidity and atmospheric pressure) were obtained from six Bureau of Meteorology weather stations in the Sydney Metropolitan area from 2005 to 2015 (data was sourced from the Bureau of Meteorology) [36]. The selected sites cover approximately 25 km from the coast to the inland border. Table1 summarises the geographical information of the selected weather stations in this study, while Figure1 shows the position of each of the six stations. All data have been submitted to detailed statistical control and cleaned of possible errors. Sydney Observatory Hill (151.2050◦E, 33.8607◦S) is the reference station in this study, which is located on the coast in the City of Sydney, almost at the heart of Sydney CBD. The City of Sydney is a mixed-use area (consisting of residential, commercial, and industrial land use), and encompasses a total land area of 2672 hectares (27 km2). According to the 2015 census data released by the Australian Sustainability 2017, 9, 712 4 of 21

BureauSustainability of Statistics,2017, 9, 712 the City of Sydney has a population of 205,339, resulting in a population density4 of 21 of 76.84 persons per hectare [32]. The City of Sydney tree canopy cover is 15.2 percent [37]. Table 1. Geographical information for the selected weather stations.

Table 1. Geographical informationLatitude forLongitude the selectedAltitude weather stations. Year Stations Region (°S) (°E) (m) Opened SydneyStations Observatory Hill Latitude 33.8607 (◦S) Longitude 151.2050 (◦E) Altitude 39 (m) CENSW Region 1 (coast) Year Opened 1858 SydneySydney Observatory Airport AMO Hill 2 33.860733.9465 151.2050151.1731 396 CENSWCENSW1 (coast)(coast) 18581929 CanterburySydney Airport Racecourse AMO 2 AWS 3 33.946533.9057 151.1731151.1134 63 CENSW CENSW (coast)(inland) 19291995 CanterburyBankstown Racecourse Airport AWS AWS3 33.9057 33.9181 151.1134 150.9864 3 7 CENSW (inland) (inland) 1995 1968 Sydney OlympicBankstown Park Airport AWS AWS(Archery Centre) 33.9181 33.8338 150.9864 151.0718 7 4 CENSW CENSW (inland) (inland) 1968 2011 Sydney Olympic Park AWS (Archery Centre) 33.8338 151.0718 4 CENSW (inland) 2011 Sydney Olympic Olympic Park Park (VIS (VIS Meter) Meter) 33.8521 33.8521 151.0646 151.0646 28 28 CENSW CENSW (inland) (inland) 1995 1995 TerreyTerrey Hills Hills AWS AWS 33.6908 33.6908 151.2253 151.2253 199 CENSW (inland) (inland) 2004 2004 Note: 1 CENSW = Central Central East New South Wales; 22 AMO = Airport Meteorological Office;Office; 3 AWS = Automatic Weather Stations.Stations.

Figure 1. Position of the considered Meteorological Stations.

SydneyAll data Airporthave been AMO submitted (151.1731 to detailed◦E, 33.9465 statis◦S)tical is locatedcontrol and onthe cleaned coast, of in possible the City errors. of Botany Bay.Sydney The City Observatory of Botany Bay Hill is (151.2050°E, located approximately 33.8607°S) is 6 the km reference south of thestation Sydney in this CBD, study, surrounded which is bylocated Sydney on the inner coast suburbs in the City on its of non-coastalSydney, almost boundaries. at the heart The ofland Sydney around CBD. the The Sydney City of AirportSydney is a mixed-use area development (consisting with of re aviationsidential, purposes, commercial, and residential,and industrial commercial, land use), and and industrial encompasses areas, a whichtotal land encompasses area of 2672 a totalhectares land (27 area km of2). 2706According hectares to (27the km20152), census including data significant released by foreshore the Australian zones. TheBureau 2015 of estimatedStatistics, the population City of Sydney for the has City a population of Botany Bayof 205,339, is 46,587 resulting with a in population a population density density of 17.22of 76.84 persons persons per per hectare hectare [32 [32].]. According The City of to Sy [37dney], tree tree canopy canopy covercover inis 15.2 the Citypercent of Botany[37]. Bay is approximatelySydney Airport 12.1 percent AMO (151.1731°E, of the total land 33.9465°S) area. is located on the coast, in the City of Botany Bay. The CityCanterbury of Botany Racecourse Bay is located AWS and approximately Bankstown Airport6 km south AWS of represent the Sydney inland CBD, suburbs surrounded of Sydney. by CanterburySydney inner Racecourse suburbs on AWS its non-coastal (151.1134◦E, boundaries 33.9057◦S) is. The located land in around Canterbury the Sydney City, southwest Airport is of a Sydney,mixed- approximatelyuse development 17 kmwith away aviation from thepurposes, Sydney and CBD residential, and 7 km from commercial, the nearest and coastline. industrial Canterbury areas, which City isencompasses mainly a residential a total land area area with of few2706 industrial hectares and(27 km commercial2), including sites. significant The City foreshore has a total zones. land areaThe of2015 about estimated 3356 hectares population (34 km for2), the with City an estimatedof Botany populationBay is 46,587 of 151,746with a popu and alation population density density of 17.22 of 45.21persons persons per hectare per hectare [32]. [ 32According]. The tree to canopy [37], covertree canopy in Canterbury cover Cityin the is aboutCity 17.5of Botany percent Bay of the is totalapproximately land area [12.137]. percent of the total land area. Canterbury Racecourse AWS and Bankstown Airport AWS represent inland suburbs of Sydney. Canterbury Racecourse AWS (151.1134°E, 33.9057°S) is located in Canterbury City, southwest of Sydney, approximately 17 km away from the Sydney CBD and 7 km from the nearest coastline. Canterbury City is mainly a residential area with few industrial and commercial sites. The City has a Sustainability 2017, 9, 712 5 of 21

Sustainabilitytotal land2017 area, 9, 712 of about 3356 hectares (34 km2), with an estimated population of 151,746 and5 a of 21 population density of 45.21 persons per hectare [32]. The tree canopy cover in Canterbury City is about 17.5 percent of the total land area [37]. ◦ ◦ BankstownBankstown Airport Airport AWS AWS (150.9864 (150.9864°E,E, 33.918133.9181°S)S) is is located located southwest southwest of of Sydney Sydney suburban suburban areas areas in Bankstownin Bankstown City, City, approximately approximately 22 22 km km South-westSouth-west of the the Sydney Sydney CBD CBD and and 16 16 km km from from the the nearest nearest coastalcoastal zone. zone. Bankstown Bankstown City City features features residential, residential, commercial commercial and and industrial industrial land land uses uses in in the the total total land arealand of 7682area hectaresof 7682 hectares (77 km2 (77) with km2 a) populationwith a population of 203,202 of 203,202 and a populationand a population density density of 26.45 of 26.45 persons perpersons hectare per [32 hectare]. The tree [32]. canopy The tree cover canopy in cover Bankstown in Bankstown City is approximatelyCity is approximately 17.1 percent 17.1 percent [37]. [37]. SydneySydney Olympic Olympic Park Park AWS AWS (Archery (Archery CentreCentre and VIS Meter Meter (Observations (Observations of ofclimate climate data data have have beenbeen drawn drawn from from Sydney Sydney Olympic Olympic Park Park AWSAWS (Archery(Archery Centre) since since 2011, 2011, which which is is2 km 2 km north north of the of the previousprevious weather weather station station at Sydneyat Sydney Olympic Olympic Park.)) Park and.)) and Terry Terry Hills Hills AWS AWS arerepresentative are representative of Sydney of inlandSydney suburbs. inland Sydneysuburbs. Olympic Sydney Olympic Park (151.0718 Park (151◦E,.0718°E, 33.8338 ◦33.8338°SS and 151.0646 and 151.0646°E,◦E, 33.8521 33.8521°S)◦S) is located is located in Auburn City, approximately 14 km west of the Sydney CBD in proximity to Parramatta in Auburn City, approximately 14 km west of the Sydney CBD in proximity to Parramatta River and River and 13 km away from the nearest coastline. Auburn City is predominately mixed-use, including 13 km away from the nearest coastline. Auburn City is predominately mixed-use, including residential residential and industrial areas with some major commercial, recreational, and parkland land uses. and industrial areas with some major commercial, recreational, and parkland land uses. Auburn City Auburn City encompasses a total land area of 3249 hectares (32 km2), with an estimated population 2 encompassesof 88,059 and a totala population land area density of 3249 of hectares27.11 persons (32 km per), hectare with an [32]. estimated Auburn populationCity encompasses of 88,059 15.4 and a populationpercent tree density canopy ofcover 27.11 for persons the total perland hectare area [37]. [32 ]. Auburn City encompasses 15.4 percent tree canopyTerrey cover forHills the AWS total (151.2253°E, land area [ 3733.6908°S)]. is part of the northern forest district positioned at 199 ◦ ◦ mTerrey above sea Hills level. AWS This (151.2253 station isE, located 33.6908 25S) km is North part of of the Sydney northern CBD forest in Warringah, district positioned 7.5 km from at the 199 m abovenearest sea level.coastline. This Warringah station is located is mainly 25 kma residential North of Sydneyarea with CBD some in Warringah,industrial and 7.5 commercial km from the sites. nearest coastline.It covers Warringah a total land is mainlyarea of 14,936 a residential hectares area (149 with km2 some) and industrialincludes a andlarge commercial area of dense sites. greenery It covers a totalsuch land as National area of 14,936 Park, hectaresbushland, (149 and km reserves.2) and includes The total a largetree canopy area of cover dense is greenery 58 percent such [37]. as There National Park,are bushland,156,693 people and reserves.estimated Theliving total in Warringah tree canopy suburban cover is areas, 58 percent with a [ 37population]. There aredensity 156,693 of 10.49 people estimatedpersons living per hectare in Warringah [32]. suburban areas, with a population density of 10.49 persons per hectare [32]. ForFor the the period period analysed, analysed, 2005–2015,2005–2015, the the ni nighttimeghttime ambient ambient temperature temperature varied varied from from −1.1 −°C1.1 to ◦C to 36.236.2 ◦°C.C. The The average, average, minimum minimum an andd maximum maximum nighttime nighttime temperatures temperatures for allfor stations all stations were from were 14.4 from 14.4°C◦ Ctoto 17.1 17.1 °C,◦ C,−1.1− 1.1°C to◦C 4 to°C, 4 and◦C, 33.9 and °C 33.9 to◦ 36.2C to °C, 36.2 resp◦C,ectively. respectively. Stations Stations located located in the western in the western part of the city (Bankstown, Canterbury and Olympic Village) presented a lower average and minimum part of the city (Bankstown, Canterbury and Olympic Village) presented a lower average and minimum nighttime temperature compared to the coastal stations of Eastern Sydney. In particular the average nighttime temperature compared to the coastal stations of Eastern Sydney. In particular the average and minimum nighttime temperatures in Western Sydney were lower by 1.3 °C and 3.3 °C than those and minimum nighttime temperatures in Western Sydney were lower by 1.3 ◦C and 3.3 ◦C than those recorded in the eastern part of the city. Insignificant differences concerning the absolute maximum recordednight time in the temperature eastern part were of observed the city. betw Insignificanteen Western differences and Eastern concerning Sydney (Figure the absolute 2). maximum night time temperature were observed between Western and Eastern Sydney (Figure2).

FigureFigure 2. 2.Variation Variation of of the the nighttime nighttime ambientambient temp temperatureerature for for the the six six considered considered stations. stations.

TheThe day day time time ambient ambient temperature during during the the stud studyy period period varied varied from from1.9 °C 1.9 to 44.6◦C to°C. 44.6 The ◦C. Themultiyear multiyear average average ambient ambient temperature temperature was was18.4 °C 18.4 in◦ TerreyC in Terrey Hills, Hills,19.2 °C 19.2 at the◦C Observatory, at the Observatory, 19.6 19.6°C◦ Cin in Canterbury, Canterbury, 20.0 20.0 °C◦ Cin inBankstown, Bankstown, 20.1 20.1 °C◦ inC inthe the Olympic Olympic Village Village and and 20.2 20.2 °C ◦atC the at theairport. airport. MinimumMinimum ambient ambient temperatures temperatures variedvaried fromfrom 1.9 °C◦C to to 4.0 4.0 °C◦C in in the the western western part part of ofthe the city city and and between 5.2 ◦C and 5.4 ◦C in the coastal eastern suburbs. The absolute maximum temperature ranged between 43.8 ◦C and 44.6 ◦C, while insignificant differences were observed between the various stations. The lowest minimum, average and maximum temperatures were observed at the Terrey Hills station, located in a green zone of Northern Sydney (Figure3). Sustainability 2017, 9, 712 6 of 21 between 5.2 °C and 5.4 °C in the coastal eastern suburbs. The absolute maximum temperature ranged Sustainability 2017, 9, 712 6 of 21 between 43.8 °C and 44.6 °C, while insignificant differences were observed between the various stations.between The 5.2 °Clowest and 5.4 minimum, °C in the coastalaverage eastern and maxi suburbs.mum The temperatures absolute maximum were observed temperature at the ranged Terrey Hillsbetween station, 43.8 located °C and in 44.6a green °C, zonewhile of insignifican Northern Sydneyt differences (Figure were 3). observed between the various stations. The lowest minimum, average and maximum temperatures were observed at the Terrey SustainabilityHills station,2017 located, 9, 712 in a green zone of Northern Sydney (Figure 3). 6 of 21

Figure 3. Variation of the daytime ambient temperature for the six considered stations. Figure 3. Variation of the daytime ambient temperature for the six considered stations. 5. NighttimeFigure Urban 3. VariationHeat Island of the Intensity daytime ambient and Characteristics temperature for the six considered stations. 5. Nighttime Urban Heat Island Intensity and Characteristics 5. NighttimeThe magnitude Urban andHeat variability Island Intensity of the nightand Characteristics time urban heat island has been calculated for the five consideredThe magnitude stations and variabilityfor the period of the between night time 2005 urban and heat2015. island The magnitude has been calculated of the Urban for the Heat five The magnitude and variability of the night time urban heat island has been calculated for the Islandconsidered is calculated stations foron the“half-hourly” period between basis. 2005 The and Observatory 2015. The station magnitude is used of the as Urbanthe reference Heat Island urban is five considered stations for the period between 2005 and 2015. The magnitude of the Urban Heat station,calculated given on “half-hourly”that it is located basis. in the The center Observatory of the city. station The isUHI used intensity as the reference in a location urban is station,calculated given as Island is calculated on “half-hourly” basis. The Observatory station is used as the reference urban thethat instant it is located difference in the of center the temperature of the city. The in the UHI area intensity minus in the a locationcorresponding is calculated temperature as the instant at the Observatory.station, given The that calculated it is located range in the of center values of isthe given city. inThe Figure UHI intensity 4. Given in that a location the nighttime is calculated ambient as differencethe instant of difference the temperature of the temperature in the areaminus in the thearea corresponding minus the corresponding temperature temperature at the Observatory. at the Thetemperature calculated in rangeWestern of valuesSydney is is given considerably in Figure lo4.wer Given than that in the coastal nighttime eastern ambient part, temperature the average magnitudeObservatory. of theThe night calculated UHI isrange negative of values at all is stat givenions in except Figure the 4. Givenairport. that The the range nighttime of the ambient average intemperature Western Sydney in Western is considerably Sydney is lowerconsiderably than in lo thewer coastal than in eastern the coastal part, theeastern average part, magnitude the average of night UHI varies between 0.12 K in the airport, −1.13 K in the Olympic Village, −1.67 K in the Terrey themagnitude night UHI of isthe negative night UHI at all is stations negative except at all thestat airport.ions except The the range airport. of the The average range night of the UHI average varies Hills, −1.95 K in Canterbury and −2.1 K in the Bankstown station. The corresponding maximum betweennight UHI 0.12 varies K in between the airport, 0.12− K1.13 in the K in airport, the Olympic −1.13 K Village, in the Olympic−1.67 K inVillage, the Terrey −1.67 Hills,K in the−1.95 Terrey K in values vary between 5.0 K to 6.7 K, while the minimum night UHI intensity is between −9.3 K and CanterburyHills, −1.95 andK in− 2.1Canterbury K in the Bankstownand −2.1 K station.in the Bankstown The corresponding station. maximumThe corresponding values vary maximum between −10.7 K for the three Western stations, (Bankstown, Canterbury and Olympic Village), and between 5.0values K to vary 6.7 K, between while the 5.0 minimum K to 6.7 K, night while UHI the intensityminimum is night between UHI− intensity9.3 K and is −between10.7 K for−9.3 the K threeand −6.5 K and −7.0 K for the airport and Terrey Hills. The maximum amplitude of the night oasis Western−10.7 K stations,for the three (Bankstown, Western Canterburystations, (Bankstown and Olympic, Canterbury Village), and and Olympic between Village),−6.5 K and and− between7.0 K for phenomenon is present in most of the stations during the early morning hours (6 a.m.) or, in some the−6.5 airport K and and −7.0 Terrey K for Hills. the airport The maximum and Terrey amplitude Hills. The of themaximum night oasis amplitude phenomenon of the isnight present oasis in rare cases, at 11 p.m. mostphenomenon of the stations is present during in themost early of the morning stations hours during (6 a.m.)the early or, in morning some rare hours cases, (6 a.m.) at 11 p.m.or, in some rare cases, at 11 p.m.

FigureFigure 4. VariabilityVariability of the nighttime UHI at the fivefive selected stations. Figure 4. Variability of the nighttime UHI at the five selected stations. The cumulative frequency distribution of the nighttime UHI for the five stations is given in Figure5. Cumulative frequency graphs help to understand the distribution of the magnitude of the urban heat island intensity during the considered period. As shown, in the western stations and Terrey Hills, the night UHI is negative for almost 90–95% of the studied period, while in the airport the UHI intensity is negative for about 50% of the time. With the exception of the Terrey Hills station, located in the proximity of a large urban greenery reserve, the frequency of negative values, as well as the Sustainability 2017, 9, 712 7 of 21

The cumulative frequency distribution of the nighttime UHI for the five stations is given in FigureSustainability 5. Cumulative 2017, 9, 712 frequency graphs help to understand the distribution of the magnitude 7of of the21 urban heat island intensity during the considered period. As shown, in the western stations and The cumulative frequency distribution of the nighttime UHI for the five stations is given in Terrey Hills, the night UHI is negative for almost 90–95% of the studied period, while in the airport Figure 5. Cumulative frequency graphs help to understand the distribution of the magnitude of the theurban UHI intensityheat island is negative intensity for during about the 50% considered of the time. period. With theAs shown,exception in ofthe the western Terrey stationsHills station, and locatedTerrey in Hills, the proximity the night UHIof a largeis negative urban for greenery almost 90–95%reserve, ofthe the frequency studied period, of negative while values, in the airport as well as theSustainability UHIabsolute intensity2017 amplitude, 9, is 712 negative of the for night about UHI, 50% increases of the time. with With distance the exception from the of co theastline. Terrey This Hills is7 station,ofbecause 21 nightlocated time in radiative the proximity and convective of a large urbancooling greenery processes reserve, are more the frequencysignificant of in negative the western values, than as inwell the eastern zones of the city, because of the decreased density, the reduced accumulated solar heat during asabsolute the absolute amplitude amplitude of the of night the UHI,night increases UHI, increases with distance with distance from the from coastline. the co Thisastline. is because This is night because thenight daytime,time time radiative radiativeand andthe proximit convective and convectivey coolingto agricultural cooling processes processes zones. are more are significant more significant in the western in the than western in the than eastern in the easternzones zones of the of city, the because city, because of the of decreased the decreased density, density, the reduced the reduced accumulated accumulated solar heat solar during heat during the thedaytime, daytime, and and the the proximity proximit toy agricultural to agricultural zones. zones.

Figure 5. Cumulative frequency distribution of the nighttime UHI intensity for the five stations. Figure 5. Cumulative frequency distribution of the nighttime UHI intensity for the five stations. A significantFigure 5. Cumulative correlation frequency is observed distribution for ofth thee nithreeghttime Western UHI intensity Sydney for thestations five stations. (Bankstown, Canterbury and Olympic Village), between the levels of the ambient temperature recorded in the AA significant significant correlationcorrelation is observedis observed for the for three th Westerne three SydneyWestern stations Sydney (Bankstown, stations Canterbury (Bankstown, reference station and the nighttime magnitude of the UHI (Figure 6). It is observed that the magnitude Canterburyand Olympic and Village), Olympic between Village), the levelsbetween of the the ambient levelstemperature of the ambient recorded temper in theature reference recorded station in the of referencetheand oasis the nighttimestationeffect inand magnitudeWestern the nighttime Sydney of the magnitude UHI is decrea (Figure of6sing). the It isand UHI observed even (Figure minimized that 6). the It magnitudeis observed during of thatthe the thewarm oasis magnitude effect summer period.ofin the Western A oasis possible effect Sydney explanation in isWestern decreasing isSydney that and in even isthe decrea western minimizedsing part and during of even the the minimizedcity, warm an important summer during period. heatingthe warm A possible mechanism summer is establishedperiod.explanation A possible during is that explanation the in thewarm western period,is that part in because ofthe the western city, of the an part importantadvection of the city, heating of anwarm important mechanism air from heating isthe established inland, mechanism while at isthe duringestablished same the time, warm during the period, Easternthe warm because Suburbs period, of the benefitbecause advection from of the of the warm advection significant air from of warm thecooling inland, air frommechanism while the at inland, the of same the while sea breeze.at time,the A same thesimilar Eastern time, phenomenon Suburbsthe Eastern benefit isSuburbs described from the benefit significant in [7]. from In cooling parallel,the significant mechanism the absolute cooling of the magnitude seamechanism breeze. A of similarof the the night sea phenomenon is described in [7]. In parallel, the absolute magnitude of the night oasis effect in Terrey oasisbreeze. effect A in similar Terrey phenomenon Hills is intensified is described during in the[7]. warmIn parallel, summer the period,absolute because magnitude of the of importantthe night Hills is intensified during the warm summer period, because of the important evapotranspiration evapotranspirationoasis effect in Terrey cooling Hills mechanism is intensified in during the area. the warm summer period, because of the important cooling mechanism in the area. evapotranspiration cooling mechanism in the area.

FigureFigure 6. Correlation 6. Correlation between between the the levels levels ofof the the ambient ambient temperature temperature recorded recorded in the referencein the reference station and station Figure 6. Correlation between the levels of the ambient temperature recorded in the reference station and thethe nighttimenighttime magnitude magnitude of the of UHI the forUHI Canterbury for Canter Stationbury (the Station red lines (the represent red lines moving represent averages). moving and the nighttime magnitude of the UHI for Canterbury Station (the red lines represent moving averages). averages).It is well known that the UHI is better developed under low wind conditions [38]. Several UHI studies in European, Asian and Australian cities have demonstrated that UHI is better developed Sustainability 2017, 9, 712 8 of 21

It is well known that the UHI is better developed under low wind conditions [38]. Several UHI studiesSustainability in European, 2017, 9, 712 Asian and Australian cities have demonstrated that UHI is better developed8 of 21 belowSustainability a threshold2017, 9wind, 712 speed that depends on the city’s characteristics [39–42]. Strong winds8 of 21 may It is well known that the UHI is better developed under low wind conditions [38]. Several UHI modifystudies the coolingin European, and Asianheating and rates Australian in both cities the haveurban demonstrated and rural environments that UHI is better and developed decrease the intensitybelowbelow of aa the thresholdthreshold UHI phenomenon. windwind speedspeed thatthat A dependsquitedepends strong onon thethe correlation city’scity’scharacteristics characteristics is found [between[39–42].39–42]. StrongStrong the wind windswinds speed maymay and the magnitudemodifymodify thethe coolingofcooling the UHI andand heatinginheating the three ratesrates inWestin bothboth Sydney thethe urbanurban stations andand ruralrural (Figure environmentsenvironments 7). For low andand wind decreasedecrease speeds, thethe the magnitudeintensityintensity of ofof thethe UHI UHInocturnal phenomenon. phenomenon. oasis A Aeffect quitequite strongstrongdeveloped correlationcorrelation in isWesternis foundfound between betweenSydney thethe is windwind significant. speedspeed andand This phenomenonthethe magnitudemagnitude is gradually ofof thethe UHIUHI reduced inin thethe as threethree wind WestWest speed Sydney Sydney increases, stations stations and (Figure (Figure is almost7 ).7). For For minimized low low wind wind for speeds, speeds, wind the thespeeds highermagnitudemagnitude than 8 m/s. of of the Higherthe nocturnal nocturnal wind oasis speedsoasis effect developed effectare associated developed in Western with in Sydney Westernimportant is significant.Sydney advection is Thissignificant. of phenomenon air masses This that tendis phenomenonto gradually minimize reduced isany gradually temperature as wind reduced speed differences. as increases, wind speed and In in isthecreases, almost airport and minimized station, is almost forthe minimized wind average speeds for magnitude wind higher speeds than of the 8 m/s. Higher wind speeds are associated with important advection of air masses that tend to minimize UHI ishigher not found than 8 to m/s. be Higheraffected wind by the speeds wind are speed; associated however, with importantits fluctuation advection is seriously of air masses reduced that close anytend temperature to minimize differences. any temperature In the airportdifferences. station, In thethe averageairport station, magnitude the ofaverage the UHI magnitude is not found of the to to zero, as convective phenomena of similar magnitude become dominant both in the reference and beUHI affected is not byfound the windto be speed;affected however, by the wind its fluctuation speed; however, is seriously its fluctuation reduced close is seriously to zero, asreduced convective close the airport stations. phenomenato zero, as convective of similar magnitudephenomena become of similar dominant magnitude both become in the reference dominant and both the in airport the reference stations. and the airport stations.

FigureFigureFigure 7. Correlation 7.7.Correlation Correlation betweenbetween between thethe the windwind wind speedspeed speed andand and the the magnitudemamagnitude ofof of thethe the UHIUHI UHI inin in thethe the threethree three WestWest West SydneySydney Sydney stationsstationsstations (the (the (thered red linesred lines lines repr represent representesent moving moving moving averages). averages). averages).

To betterToTo better better demonstrate demonstrate demonstrate the the the relation relation relation between between between the the magnitude mamagnitude of of of the the the nocturnal nocturnal nocturnal oasis oasis oasis effect,effect, effect, thethe windthewind wind speedspeedspeed andand theand theambientthe ambientambient temperature temperaturetemperature levels, levels, levels, the the the availabl available available datadata for forfor thethe the stationstation station inin CanterburyinCanterbury Canterbury havehave have beenbeen been classifiedclassifiedclassified in 11 in in wind 11 11 wind wind speed speed speed clusters clusters clusters from from from 0 0 0to to 11 11 m/s.m/s. m/s. TheThe averageaverage windwind wind speed,speed, speed, ambientambient ambient temperaturetemperature temperature and nocturnal UHI intensity were calculated for each cluster. Their correlation is plotted in Figure 8. and nocturnaland nocturnal UHI UHI intensity intensity were were calculated calculated for for each each cluster.cluster. Their Their correlation correlation is plottedis plotted in Figure in Figure8. 8. AsAs shown,shown, thethe magnitude magnitude ofof the the nocturnal nocturnal oasis oasis phenomenon phenomenon decreasesdecreases considerablyconsiderably underunder strongstrong As shown, the magnitude of the nocturnal oasis phenomenon decreases considerably under strong windwind conditions, conditions, while while low low wind wind speedsspeeds correspondcorrespond to to highhigh magnitudesmagnitudesof ofthe thenocturnal nocturnaloasis oasis effecteffect wind conditions, while low wind speeds correspond to high magnitudes of the nocturnal oasis effect andand higher higher average average ambient ambient temperatures. temperatures. Under Unde similarr similar average average temperature temperature conditions, conditions, the intensity the and ofhigherintensity the wind average of speedthe wind determinesambient speed determines temperatures. almost completely almost Unde comp therletely magnitude similar the magnitude average of the nocturnal oftemperature the nocturnal oasis effect, conditions, oasis and effect, low the intensitywindand lowof speeds the wind wind help speeds tospeed develop help determines to a develop stronger almost a oasisstronger phenomenon.comp oasisletely phenomenon. the magnitude of the nocturnal oasis effect, and low wind speeds help to develop a stronger oasis phenomenon.

FigureFigure 8.8. CorrelationCorrelation betweenbetween thethe averageaverage windwind speed,speed, ambientambient temperature,temperature, andand nocturnalnocturnal UHIUHI intensityintensity as as calculated calculated for for each each cluster. cluster. Figure 8. Correlation between the average wind speed, ambient temperature, and nocturnal UHI

intensity as calculated for each cluster.

Sustainability 2017, 9, 712 9 of 21 SustainabilitySustainability 20172017, ,99, ,712 712 9 of9 of 21 21 6. Daytime Urban Heat Island Intensity and Characteristics 6. Daytime Urban Heat Island Intensity and Characteristics 6. DaytimeThe day Urban time (8 Heat a.m.–8 Island p.m.) Intensity intensity and of the Characteristics urban heat island is calculated for the whole 10 year period.The The day magnitudes time (8 a.m.–8 of p.m.)the UHI intensity at all stationsof the urban are given heat island in Figure is calculated 9. The spatial for the distribution whole 10 year of The day time (8 a.m.–8 p.m.) intensity of the urban heat island is calculated for the whole 10 year period.temperature The magnitudes differences acrossof the UHIthe city at all is stationscharacterized are given by an in importantFigure 9. Thevariability, spatial distributionwhich results of temperatureperiod. The differences magnitudes across of the UHIthe city at all is stationscharacterized are given by inan Figureimportant9. The variability, spatial distribution which results of eithertemperature in the development differences across of a strong the city positive is characterized or negative by urban an important heat island. variability, The 99% which percentile results of eitherthe maximum in the development UHI intensity of a instrong the threepositive stations or negative of Western urban Sydneyheat island. varies The between 99% percentile 3.8 K inof theeither maximum in the development UHI intensity of a strongin the positive three stations or negative of urbanWestern heat Sydney island. Thevaries 99% between percentile 3.8 of theK in Canterbury,maximum UHI 5.1 intensityK in the inOlympic the three Village, stations and of Western5.7 K in SydneyBankstown. varies In between parallel, 3.8 the K incorresponding Canterbury, Canterbury, 5.1 K in the Olympic Village, and 5.7 K in Bankstown. In parallel, the corresponding values5.1 K inat thethe OlympicAirport and Village, in Terrey and 5.7Hills K inare Bankstown. close to 3.2 K In and parallel, 2.7 K therespectively. corresponding The 99% values percentile at the values at the Airport and in Terrey Hills are close to 3.2 K and 2.7 K respectively. The 99% percentile ofAirport the intensity and in Terreyof the Hillsdeveloped are close oasis to 3.2phenomenon K and 2.7 K varies respectively. between The −2.7 99% K percentileand −5.1 K of in the all intensity stations. of the intensity of the developed oasis phenomenon varies between −2.7 K and −5.1 K in all stations. Theof the absolute developed maximum oasis phenomenon UHI intensity varies in Western between −Sydney2.7 K andmay− 5.1reach K in7–10 all stations.K while The the absoluteabsolute The absolute maximum UHI intensity in Western Sydney may reach 7–10 K while the absolute maximummaximum intensity UHI intensity of the in developed Western Sydney oasis phenomen may reachon 7–10 is of K whilethe same the order absolute of magnitude. maximum intensity maximum intensity of the developed oasis phenomenon is of the same order of magnitude. of the developed oasis phenomenon is of the same order of magnitude.

Figure 9. Levels of daytime UHI magnitude at all stations. Figure 9. Levels of daytime UHI magnitude at all stations. Figure 9. Levels of daytime UHI magnitude at all stations. Figure 10 presents the day time cumulative frequency distribution of the UHI at the five stations. As shown,FigureFigure UHI 10 10 presents presents is positive the the forday day 61%, time time 54%, cumulative 52%, 40% frequencyfreque andncy 11% distributiondistribution of the time of ofin the the UHI UHIstations at at the the of five fivethe stations. Airport, stations. AsOlympicAs shown, shown, Village, UHI UHI is is Bankstow positive positive for forn, Canterbury61%, 54%, 52%, and 40%Terrey andand Hills, 11%11% respectively. ofof thethetime time in in the the stations stations of of the the Airport, Airport, OlympicOlympic Village, Village, Bankstow Bankstown,n, Canterbury andand TerreyTerrey Hills, Hills, respectively. respectively.

FigureFigure 10. 10. DaytimeDaytime cumulative cumulative frequency distributiondistribution ofof thethe UHIUHI inin thethe five five stations. stations. Figure 10. Daytime cumulative frequency distribution of the UHI in the five stations. Given the variability of the UHI intensity observed mainly in the western part of the city, a detailedGiven analysis the variability aimed at ofinvestigating the UHI intensity the reasons observed for the mainly UHI characteristics in the western has part been of performed the city, a detailedfor the Bankstown analysis aimed station. at investigating The station presents the reasons the forhighest the UHI and characteristicslowest UHI intensities has been during performed the forstudied the Bankstown period and isstation. characterized The station by a significantpresents the annual highest variability. and lowest It is alsoUHI the intensities most characteristic during the studiedamong allperiod stations and locat is characterizeded in Western by Sydney.a significant annual variability. It is also the most characteristic among all stations located in Western Sydney. Sustainability 2017, 9, 712 10 of 21

Given the variability of the UHI intensity observed mainly in the western part of the city, a detailed analysisSustainability aimed 2017, 9 at, 712 investigating the reasons for the UHI characteristics has been performed for10 of the 21 Bankstown station. The station presents the highest and lowest UHI intensities during the studied periodUsing and isfuzzy characterized clustering by techniques, a significant all annual data variability.are classified It is into also five the mostclusters characteristic according amongto the allmagnitude stations locatedof the UHI in Western intensity. Sydney. The first cluster corresponds to high positive UHI values and is centredUsing on fuzzyUHI intensity clustering equal techniques, to 4.9 K. allThis data clus areter classifiedincludes almost into five 3.8% clusters of the accordingwhole data. to The the magnitudesecond cluster, of the corresponds UHI intensity. to Themoderate first cluster positive corresponds UHI intensities, to high positiveis centred UHI on valuesUHI intensity and is centred equal onto 1.84 UHI K, intensity and includes equal to 39% 4.9 K.of Thisthe data. cluster The includes third cluster almost corresponds 3.8% of the whole to small data. positive The second or negative cluster, correspondsUHI intensities, to moderate is centred positiveat 0.23 K UHI and intensities,includes 33.4% is centred of the ondata, UHI while intensity the fourth equal cluster to 1.84 includes K, and includessmall negative 39% of UHI the data. intensities, The third is centred cluster correspondsat −0.93 K and to smallinvolves positive 16.5% or of negative the data. UHI Finally, intensities, the last is centredcluster is at centred 0.23 K and at − includes3.35 K, includes 33.4% of medium the data, and while high the nega fourthtive cluster UHI intensities includes small and contains negative 7.3% UHI intensities,of the data. is centred at −0.93 K and involves 16.5% of the data. Finally, the last cluster is centred at −3.35First K, includes Cluster: mediumHigh Positive and high UHI negative Intensity UHI. The intensities first cluster and includes contains data 7.3% for of thethe data.periods when the UHIFirst Cluster:intensity High varied Positive between UHI 11.25 Intensity. K and The 3.6 first K. cluster The includescorresponding data for levels the periods of the whenambient the UHItemperature, intensity wind varied speed between and 11.25 wind K direction and 3.6 K. in The the correspondingreference and levelsthe Bankstown of the ambient stations temperature, are given windin Figure speed 11. and The wind ambient direction temperature in the reference in the refe andrence the station Bankstown varied stations between are 13.2 given °C inand Figure 35.5 °C,11. Thewith ambient an average temperature close to 25.7 in the °C, reference while in station the Bank variedstown between station 13.2 it varied◦C and between 35.5 ◦C, 16.9 with °C an and average 41.8 close°C with to 25.7 an average◦C, while around in the Bankstown30.8 °C. The station wind itspe varieded at between both stations 16.9 ◦ Cwas and quite 41.8 ◦similarC with and an average varied aroundbetween 30.8 0.3 ◦m/sC. Theand wind12 m/s, speed with at an both average stations close was to 5 quite m/s. similar and varied between 0.3 m/s and 12 m/s,However, with an a average very important close to 5 m/s.difference was observed concerning the wind direction in both stations.However, The reference a very important station was difference mainly was exposed observed to low-temperature concerning the wind easterly direction winds in coming both stations. from Thethe referenceocean direction, station waswhile mainly in the exposed Bankstown to low-temperature station, a significant easterly part winds of the coming wind from was thefrom ocean the direction,western direction while in the(Figure Bankstown 12). Westerly station, winds a significant in summer part of are the of wind quite was high from temperature the western and direction come (Figurefrom the 12 inland). Westerly desert winds area. in All summer the observed are of quite case highs with temperature very high UHI and comeintensities from thecorresponded inland desert to area.westerly All winds the observed in the Bankstown cases with station. very high When UHI th intensitiese prevailing corresponded winds in the to Bankstown westerly windsstation in were the Bankstownfrom the east, station. and with When a very the high prevailing degree windsof probability in the Bankstown they corresponded station wereto a weak from penetration the east, and of withthe sea a very breeze, high the degree UHI ofintensity probability was theyat the corresponded lower limits toof athis weak cluster. penetration The combination of the sea breeze,of easterly the UHIand southeasterly intensity was low-temperature at the lower limits winds of this in cluster. the refe Therence combination station together of easterly with andthe westerly southeasterly high low-temperaturetemperature winds winds in the in theBlacktown reference station station is together the main with reason the westerly for the highvery temperaturehigh UHI intensities winds in theobserved. Blacktown station is the main reason for the very high UHI intensities observed.

FigureFigure 11. Levels of the daytime ambient temperature, windwind speed and wind direction in the reference andand thethe BankstownBankstown stationsstations inin thethe firstfirst cluster.cluster. Sustainability 2017, 9, 712 11 of 21 Sustainability 2017, 9, 712 11 of 21

Sustainability 2017, 9, 712 11 of 21

FigureFigure 12. 12.Frequency Frequency of of the the daytime daytime wind wind direction direction in in the the reference reference and and the the Bankstown Bankstown station stationfor forthe fivethe clusters. five clusters. Figure 12. Frequency of the daytime wind direction in the reference and the Bankstown station for the five clusters. SecondSecond Cluster: Cluster: Moderate Moderate Positive Positive UHI UHI intensity. intensity. The The second second cluster cluster includes includes climatic climatic data data where where the UHI intensity was between 1.0 K and 3.6 K. The corresponding ambient temperature, wind the UHISecond intensity Cluster: was between Moderate 1.0 Positive K and 3.6 UHI K. Theintensity. corresponding The second ambient cluster temperature,includes climatic wind data speed speed and wind direction conditions in both the reference and the Bankstown stations are given in andwhere wind the direction UHI intensity conditions was inbetween both the 1.0 referenceK and 3.6 andK. The the corresponding Bankstown stations ambient are temperature, given in Figure wind 13. Figure 13. The ambient temperature in the reference station ranged from 3.4 °C to 41.6 °C, with an Thespeed ambient and temperature wind direction in theconditions reference in stationboth the ranged reference from and 3.4 the◦C Bankstown to 41.6 ◦C, stations with an are average given closein average close to 22 °C. Ambient temperature in the Bankstown station varied between 8.6 °C and 44.5 to 22Figure◦C. Ambient 13. The ambient temperature temperature in the Bankstownin the reference station station varied ranged between from 3.4 8.6 °C◦C to and 41.6 44.5 °C,◦ withC with an an °C with an average close to 23.9 °C. As observed, the levels of ambient temperature in this second averageaverage close close to to 23.9 22 ◦°C.C. Ambient As observed, temperature the levels in the of ambientBankstown temperature station varied in thisbetween second 8.6 cluster°C and 44.5 are on cluster are on average substantially lower than those in the first cluster. Similar to the night period, °C with an average close to 23.9 °C. As observed, the levels of ambient temperature in this second averagevery high substantially UHI intensities lower thancorrespond those in to the higher first cluster.ambient Similar temperatures. to the night The period,wind speed very in high both UHI cluster are on average substantially lower than those in the first cluster. Similar to the night period, intensitiesstations correspondwas quite similar to higher and varied ambient between temperatures. 0 and 14 m/s, The windwith an speed average in both close stations to 5 m/s. was Wind quite very high UHI intensities correspond to higher ambient temperatures. The wind speed in both similarspeed and conditions varied between in this second 0 and cluster 14 m/s, are with similar an averageto the ones close observed to 5 m/s. in the Wind first speed cluster. conditions Wind in in stations was quite similar and varied between 0 and 14 m/s, with an average close to 5 m/s. Wind thisthe second reference cluster station are similarwas from to eastern, the ones NE observed and SE indirections, the first while cluster. in Windsome cases in the winds reference from station the speed conditions in this second cluster are similar to the ones observed in the first cluster. Wind in waswest from were eastern, observed. NE andAs already SE directions, mentioned, while winds in someof NE, cases SE, and winds Eastern from orientations the west wereare from observed. the the reference station was from eastern, NE and SE directions, while in some cases winds from the Asocean already side mentioned, and are of winds relatively of NE, low SE, temperature. and Eastern At orientationsthe Bankstown are station, from the high ocean frequencies side and of are west were observed. As already mentioned, winds of NE, SE, and Eastern orientations are from the of relativelyeasterly winds low temperature.were observed, At probably the Bankstown correspo station,nding to high a weak frequencies penetration of easterlyof the sea winds breeze. were ocean side and are of relatively low temperature. At the Bankstown station, high frequencies of Under these conditions the UHI intensity was close to the lower limits of the present cluster. On the observed,easterly probably winds were corresponding observed, probably to a weak correspo penetrationnding of to the a seaweak breeze. penetration Under of these the conditionssea breeze. the contrary, when the wind was flowing from western orientations, the UHI intensity was close to the UHIUnder intensity these was conditions close to the the UHI lower intensity limits ofwas the close present to the cluster. lower Onlimits the of contrary, the present when cluster. the windOn the was upper limit of the present cluster, in a similar way as in the first cluster. flowingcontrary, from when western the orientations,wind was flowing the UHI from intensity western was orientations, close to the the upper UHI intensity limit of thewas present close to cluster, the in aupper similar limit way of asthe in present the first cluster, cluster. in a similar way as in the first cluster.

Figure 13. Levels of the daytime ambient temperature, wind speed and wind direction in the reference and the Bankstown stations in the second cluster. FigureFigure 13. 13.Levels Levels of of the the daytime daytime ambient ambienttemperature, temperature, windwind speed speed and and wind wind dire directionction in inthe the reference reference and the Bankstown stations in the second cluster. andThird the Bankstown Cluster: Negligible stations in UHI the second intensity. cluster. The third cluster includes climatic data corresponding to low UHI intensities ranging between −0.3 K and 1.0 K. The corresponding ambient temperature, Third Cluster: Negligible UHI intensity. The third cluster includes climatic data corresponding windThird speed Cluster: and wind Negligible direction UHI data intensity. for the referenc The thirde and cluster the Bankstown includes climatic stations data are given corresponding in Figure to to low UHI intensities ranging between −0.3 K and 1.0 K. The corresponding ambient temperature, low UHI intensities ranging between −0.3 K and 1.0 K. The corresponding ambient temperature, wind wind speed and wind direction data for the reference and the Bankstown stations are given in Figure Sustainability 2017, 9, 712 12 of 21

Sustainability 2017, 9, 712 12 of 21 speedSustainability and wind 2017, 9 direction, 712 data for the reference and the Bankstown stations are given in Figure12 of 21 14 . ◦ ◦ The14. ambient The ambient temperature temperature in the in reference the reference station stat variedion varied between between 6.3 C 6.3 and °C 43.7 and C43.7 with °C an with average an ◦ ◦ ◦ closeaverage14. toThe 19.9 closeambientC, to while 19.9 temperature °C, the while temperature inthe the temperature reference in the Bankstown instat theion Bankstown varied station between rangedstation 6.3 ranged between °C and between 6.2 43.7C °C and6.2 with °C 44.1 and anC, ◦ with44.1average an °C, average withclose anto around 19.9average °C, 20.2 whilearoundC. Thethe 20.2 temperature wind °C. speed The wind wasin the veryspeed Bankstown similar was very in station both similar stations ranged in both rangingbetween stations from 6.2 ranging °C 0.0 and m/s tofrom44.1 14 m/s, °C, 0.0 withm/s with to an an 14 average averagem/s, with around close an average to 20.2 4.7 °C. m/s.close The to The wind 4.7 wind m/s. speed The direction waswind very direction did similar not differ did in not both significantly differ stations significantly ranging between thebetweenfrom two 0.0 stations m/sthe totwo 14 and m/s,stations the with air and an was average the mainly air closewas blowing mainlyto 4.7 m/s. from blowing The Southern, wind from direction Southern, Eastern, did and Eastern,not differ Western and significantly directions.Western Givendirections.between that the in Given both two stationsthatstations in both theand wind stationsthe air speed wasthe andwindmainly wind speed blowing direction and windfrom followed Southern,direction quite followedEastern, similar andquite patterns, Western similar the strengthpatterns,directions. of the Given strength developed that of in the UHIboth developed intensity stations UHI wasthe windin quitetensity speed reduced was and quite and wind reduced close direction to zero.and closefollowed to zero. quite similar patterns, the strength of the developed UHI intensity was quite reduced and close to zero.

FigureFigure 14. 14.Levels Levels of of the the daytime daytime ambientambient temperature, wi windnd speed speed and and wind wind dire directionction in in the the reference reference andandFigure the the Bankstown 14. Bankstown Levels of stations thestations daytime in in the the ambient third third cluster. cluster. temperature, wind speed and wind direction in the reference and the Bankstown stations in the third cluster. FourthFourth Cluster: Cluster: Moderate Moderate NegativeNegative UHIUHI intensity. The fourth fourth cluster cluster includes includes climatic climatic data data for for Fourth Cluster: Moderate Negative UHI intensity. The fourth cluster includes climatic data for allall cases cases corresponding corresponding toto moderate negative negative UHI UHI intensities intensities ranging ranging between between −0.3− K0.3 and K − and2 K. −The2 K. correspondingall cases corresponding data for the to moderateambient temperature, negative UHI wi intensitiesnd speed andranging wind between direction −0.3 in bothK and the −2 stations K. The The corresponding data for the ambient temperature, wind speed and wind direction in both the arecorresponding given in Figure data 15. for The the ambient temperaturetemperature, in wi thend referencespeed and station wind directionwas between in both 6 °C the and stations 45 °C stations are given in Figure 15. The ambient temperature in the reference station was between 6 ◦C withare given an average in Figure close 15. to The 18.9 ambient °C, while temperature in the station in the of referenceBankstown station the ambient was between temperature 6 °C and ranged 45 °C and 45 ◦C with an average close to 18.9 ◦C, while in the station of Bankstown the ambient temperature betweenwith an average 4 °C and close 44.6 to °C, 18.9 with °C, an while average in the around station 18 of °C. Bankstown The wind the speed ambient levels temperature were quite rangedlow in ranged between 4 ◦C and 44.6 ◦C, with an average around 18 ◦C. The wind speed levels were quite bothbetween stations 4 °C rangingand 44.6 from °C, with0 to 15an m/s,average with around an average 18 °C. close The to wind 4 m/s. speed Southern levels andwere western quite low wind in low in both stations ranging from 0 to 15 m/s, with an average close to 4 m/s. Southern and western directionsboth stations were ranging predominant from 0 to in 15 both m/s, stations. with an Usually, average southerlyclose to 4 m/s.and westerlySouthern windsand western had to windflow windoverdirections directions the dense were werepart predominant of predominant the city inbefore both in reaching bothstations. stations. thUsually,e reference Usually, southerly station, southerly and which westerly and was westerly notwinds the windshadcase tofor hadflow the to flowBankstownover over the thedense station. dense part part ofThe the of above, thecity citybefore in beforecombination reaching reaching th wie reference theth the reference significantly station, station, which higher which was anthropogenicnot was the not case the for case heat the for thegeneratedBankstown Bankstown around station. station. the The reference The above, above, station,in in combination combination resulted inwi withath slight the the significantlyoverheating significantly ofhigher higher the reference anthropogenic anthropogenic zone and heat heat a generatedmoderategenerated around negativearound the theUHI reference reference intensity. station,station, resulted in in a a slight slight overheating overheating of ofthe the reference reference zone zone and and a a moderatemoderate negative UHI intensity. intensity.

Figure 15. Levels of the daytime ambient temperature, wind speed and wind direction in the reference FigureandFigure the 15. 15. BankstownLevels Levels of of the thestations daytime daytime in theambient ambient fourth temperature,temperature, cluster. wi windnd speed speed and and wind wind direction direction in in the the reference reference andand the the Bankstown Bankstown stations stations in in the the fourth fourth cluster. cluster. Sustainability 2017, 9, 712 13 of 21 Sustainability 2017, 9, 712 13 of 21 Sustainability 2017, 9, 712 13 of 21 Fifth Cluster: Medium and High Negative UHI intensity. The fifth cluster includes data from all casesFifth where Cluster: the UHI Medium intensity and was High negative Negative and UHI between intensity. −2.0 TheK and fifth fifth −6.2 cluster K. The includes corresponding data from data all casesof the where ambient thethe temperature, UHIUHI intensityintensity wind waswas negativespeednegative and andand wind between between direction− −2.0 for KK andandboth −− stations6.26.2 K. K. The The are corresponding corresponding given in Figure data 16. ofThe the ambient ambient temperature temperature, in wind the reference speed and station wind va di directionriedrection between for both 5.4 °Cstations stations and 36.9 are are °Cgiven given with in in an Figure Figure average 16.16. Thevalue ambient around temperature 16.5 °C, while in at the the referencereference Bankstown stationstation station variedvaried temperature betweenbetween 5.45.4 fluctuated ◦°CC and 36.9between ◦°CC with 1.9 °C an and average 31.9 value°C with around an average 16.5 16.5 °C,◦ C,close while while to at 13.4 at the the °C.Bankstown Bankstown The cluster station station is characterized temperature temperature byfluctuated fluctuatedconsiderably between between low 1.9 wind °C 1.9 and ◦speeds.C 31.9 and 31.9°CThe with average◦C withan average wind an average speed close atto close the 13.4 reference to °C. 13.4 The◦C. andcluster The Bankst clusteris characterizedown is stations characterized byare considerably 3 m/s by and considerably 1.6 low m/s wind respectively. low speeds. wind speeds.TheThus, average the The convective wind average speed windand at the speedadvective reference at the phenomena, and reference Bankst and ownlike Bankstown stationssea breeze, are stations 3were m/s andnot are 1.6 3important m/s m/s andrespectively. 1.6and m/s the respectively.Thus,temperature the convective Thus,difference the convectiveand was advective mainly and due advectivephenomena, to the phenomena,ma gnitudelike sea of likebreeze, the sea sensible breeze,were andnot were anthropogenicimportant not important and heat andthe thetemperaturegenerated temperature in differenceeach difference place. was was mainly mainly due due to tothe the ma magnitudegnitude of of the the sensible sensible and and anthropogenic anthropogenic heat generated in each place.

Figure 16. Levels of the daytime ambient temperature, wind speed and wind direction in the reference Figureand the 16. Bankstown LevelsLevels of of the thestations daytime daytime in the ambient ambient fifth cluster. temperature, temperature, wi windnd speed and wind dire directionction in the reference and the Bankstown stations in the fifthfifth cluster.cluster. Similar phenomena are also occurring and similar explanations are valid for the other two stationsSimilar located phenomenaphenomena in Western are are Sydney also also occurring occurring (Canterbury and and similar and similar Olympic explanations explanations Village). are validAt are both forvalid stations, the for other the an two otherimportant stations two locatedstationsincrease inlocated in Western the UHI in Western Sydney intensity (CanterburySydney is observed (Canterbury and for Olympic increasing and Olympic Village). ambient Village). At temperatures both stations,At both stations,(Figure an important 17) an becauseimportant increase of inincreasethe the important UHI in the intensity UHIadvective intensity is observed and is observedconvective for increasing for increasingphenomena ambient ambient associated temperatures temperatures with (Figure the (Figure particular17) because 17) because synoptic of the of importanttheconditions. important advective advective and convective and convective phenomena phenomena associated associated with the particularwith the synoptic particular conditions. synoptic conditions.

Figure 17. Levels of UHI intensity for different ambientambient temperatures atat thethe OlympicOlympic Village.Village. Figure 17. Levels of UHI intensity for different ambient temperatures at the Olympic Village. Sustainability 2017, 9, 712 14 of 21

As concerns the station of Terrey Hills, the UHI is positive for 13.7% of the time, while for the rest of the period the ambient temperature is lower than in the reference station. Using clustering techniques, all data have been classified in three clusters. The first cluster is centred at 0.78 K, and includes all climatic data corresponding to the positive values of the UHI intensity ranging between −0.3 and 6.4 K. An analysis of the relevant climatic data in the cluster shows that high UHI values occur during the rare periods when the wind in Terrey Hills is from the inland area (western direction), while in the reference station the air is coming from the sea, Eastern direction. Under these synoptic conditions, warm air is advected in Terrey Hills, while, in parallel, low-temperature air is advected in the reference station, resulting in an important UHI intensity. The second cluster is centred around an UHI intensity close to −1.3 K and includes almost 46% of the data. The UHI ranges between −0.3 and −1.9 K. The wind speed and direction are similar in both stations and the small negative UHI intensity is because of the additional anthropogenic heat in the reference station and the significant cooling rates caused by the evapotranspiration in Terrey Hills. Finally, the last cluster includes the climatic data corresponding to the high negative UHI intensities, up to −4.0 K. The maximum negative values occur when the wind in the reference station is flowing from the western direction, advecting warmer air to the station, while in Terrey Hills cooler air is flowing from northern and northeastern directions. Finally, an analysis of the UHI intensity in the airport area has been performed using the same methodology as previously. Three clusters of climatic data have been defined. The first cluster includes all data corresponding to UHI intensities between 0.9 K and 5 K; it is centred at 1.6 K and includes almost 28% of the data. High positive UHI values are observed only when the air flow in the airport is from the mainland, western direction, while at the reference station it is from the sea direction. The second cluster includes all data corresponding to low UHI intensities ranging between −0.7 K and 0.9 K. This cluster includes almost 56% of the data. The climatic conditions at both stations are quite similar and the observed temperature differences are due to the local heat effects. Finally, the third cluster includes all data corresponding to UHI intensities lower than −0.7 K and is centred around −1.4 K. Quite important negative UHI intensities are observed only when the wind speed at the reference station is from the inland, western direction, while at the airport it is from the sea direction. The whole analysis reveals that the development and magnitude of the UHI in the city are mainly governed by advection processes. The sea breeze is the main cooling mechanism in the city, while westerly winds from the country inland present the main heating mechanism during the warm period. During the summer, both mechanisms may co-exist, resulting in high temperature differences between the eastern and western parts of the city. Several other synoptic conditions and combinations may occur, resulting in smaller UHI intensities. A significant oasis phenomenon is also observed, mainly during the winter period, and during the days where the strength of the sea breeze is not significant and the heat generated in the city is not removed.

7. Spatial Distribution of the Cooling Degree Days The severity of the climate and the resulting cooling energy demand can be described in terms of cooling degree days (CDDs). The cooling degree days (CDD) index was used in this analysis due to its correlation with UHI and energy consumption. Therefore, the annual cooling degree days were calculated with a base temperature of 23 ◦C, as a measure of cooling energy demand, for different locations in Greater Sydney based on the data from the six stations, enriched with additional data provided by the BizEE Degree Days online software tool [43]. This online tool uses temperature data from Weather Underground [44]. ArcGIS 10.3 (ArcGIS, Version 10.3, Esri, Redlands, CA, USA) software was used to obtain the exact location, analyse the spatial data, and illustrate the area under specified thermal conditions. The widely used Inverse Distance Weighted (IDW) interpolation technique was implemented to generate the spatial patterns of annual CDDs on the map. This method is based on the assumption that the nearest points surrounding a selected location have more influence on the prediction than those that are farther away. The IDW interpolation technique weights the points Sustainability 2017, 9, 712 15 of 21 Sustainability 2017, 9, 712 15 of 21 weights the points being evaluated based on the distance from the sampled location; the weight is a functionbeing of evaluated inverse distance based on the[45]. distance from the sampled location; the weight is a function of inverse distanceFor the calculation [45]. of CDDs, the period 2014–2016 was selected. It should be noted that detailed temperatureFor thereadings, calculation taken of CDDs,throughout the period each 2014–2016 day for the was six selected. weather It should stations be notedselected that in detailed this study, temperature readings, taken throughout each day for the six weather stations selected in this study, enable an intensive calculation process (the so-called Integration Method) to increase the accuracy of enable an intensive calculation process (the so-called Integration Method) to increase the accuracy of the resulting degree day data [43]. The calculated CDDs for the selected sites and years are shown in the resulting degree day data [43]. The calculated CDDs for the selected sites and years are shown in FigureFigure 18. 18 .

FigureFigure 18. 18. CalculatedCalculated CDDs CDDs for thethe selectedselected sites sites and and years. years.

The Theresult result indicates indicates that that annual annual cooling cooling degree-day degree-dayss ranged ranged from from 89 89 to to 215 215 in 2014,in 2014, being being higher higher ◦ ◦ in Bankstownin Bankstown with with 215 215 °C day,C day, followed followed by by Sydney Sydney OlympicOlympic Park Park (203 (203C °C day). day). In contrast,In contrast, the lowestthe lowest ◦ CDDsCDDs is calculated is calculated for for Terrey Terrey Hills Hills Reserve Reserve with with 89 °CC dayday located located in in the the hilly hilly forest forest district district followed followed by Sydney Observatory Hill (133 ◦C day) located adjacent to Sydney Harbour in the coastal zone. by Sydney Observatory Hill (133 °C day) located adjacent to Sydney Harbour in the coastal zone. In In 2015, CDD values varied between 118 and 240, with a similar pattern observed in 2014. The trend 2015, CDD values varied between 118 and 240, with a similar pattern observed in 2014. The trend of of calculated CDDs in 2015–2016 is consistent with those in 2015 and 2014; however, CDDs have calculatedincreased CDDs to 261 in◦ C2015–2016 day in Bankstown is consistent and 126 with◦C day those in Terrey in 2015 Hills and Reserve. 2014; The however, obtained rangeCDDs of have increasedCDDs to and 261 the °C spatial day in pattern Bankstown appear toand be 126 influenced °C day by in topographyTerrey Hills and Reserve. water proximity. The obtained range of CDDs andFigures the spatial 19–21 illustratepattern appear CDDs mapsto be forinfluenced Sydney Observatory by topography Hill, and Sydney water Airport, proximity. Canterbury Racecourse,Figures 19–21 Bankstown illustrate Airport CDDs AWS, maps Sydney for Sydney Olympic Observatory Park AWS, andHill, Terrey Sydney Hills Airport, Reserve Canterbury in 2014 Racecourse,and 2015, Bankstown and 2015–2016 Airport respectively. AWS, Sydney Figures Olym 19–21pic suggest Park AWS, that CDDs and Terrey are clearly Hills different Reserve from in 2014 and station2015, and to station, 2015–2016 showing respectively. a great spatial Figures variability. 19–21 Thesuggest areas that located CDDs in the are west clearly and southwest,different from stationwhere to station, Bankstown showing airport a station great isspatial located, variabi are characterizedlity. The areas by higherlocated annual in the CDDs westcompared and southwest, to whereObservatory Bankstown Hill airport in Sydney station CBD is andlocated, Terry are Hills characterized located in the by northern higher annual suburbs. CDDs This patterncompared is to consistent for all investigated years. However, CDDs have increased more drastically in recent years. Observatory Hill in Sydney CBD and Terry Hills located in the northern suburbs. This pattern is The average annual CDD in 2016 is up to 47 ◦C day higher than that in 2014. This implies a growing consistent for all investigated years. However, CDDs have increased more drastically in recent years. cooling energy demand throughout Sydney. The averageSince annual CDD isCDD an important in 2016 is index up to reflecting 47 °C day the higher climate than and that energy in 2014. demand This of implies buildings, a growing the coolinganalysis energy is extendeddemand throughout to calculate theSydney. cooling degree days of a larger region and compare CDD calculations for 24 different locations across the Sydney metropolitan area. Table2 summarises the geographical location and CDDs of the extended weather stations based on data from November 2015 to October 2016. The spatial pattern of cooling degree days calculated for 24 sites is illustrated on the map (Figure3). The results of such an investigation foster a better understanding of the climate and energy consumption of buildings in different climatic conditions. It should be noted that the Degree Day.net online tool is programmed to estimate CDD to account for missing temperature data [43]. Sustainability 2017, 9, 712 16 of 21 Sustainability 2017, 9, 712 16 of 21 Sustainability 2017, 9, 712 16 of 21

Figure 19. CDDs maps for Sydney Observatory Hill, Sydney Airport, Canterbury Racecourse, FigureFigure 19. 19. CDDsCDDs maps maps for for Sydney Sydney Observatory Observatory Hill, SydneySydney Airport,Airport, CanterburyCanterbury Racecourse, Racecourse, Bankstown Airport AWS, Sydney Olympic Park AWS, and Terrey Hills Reserve in 2014. BankstownBankstown Airport Airport AWS, AWS, Sydney Sydney Olympic Olympic Park AWS,AWS, and and Terrey Terrey Hills Hills Reserve Reserve in in 2014. 2014.

Figure 20. CDDs maps for Sydney Observatory Hill, Sydney Airport, Canterbury Racecourse, Figure 20. CDDs maps for Sydney Observatory Hill, Sydney Airport, Canterbury Racecourse, BankstownFigure 20. AirportCDDs AWS, maps Sydney for Sydney Olympic Observatory Park AWS, Hill, and Sydney TerreyAirport, Hills Reserve Canterbury in 2015. Racecourse, BankstownBankstown Airport Airport AWS, AWS, Sydney Sydney Olympic Olympic ParkPark AWS,AWS, and and Terrey Terrey Hills Hills Reserve Reserve in in 2015. 2015. Sustainability 2017, 9, 712 17 of 21 Sustainability 2017, 9, 712 17 of 21

FigureFigure 21. 21. CDDsCDDs maps maps for for Sydney Sydney Observatory Observatory Hill, SydneySydney Airport,Airport, CanterburyCanterbury Racecourse, Racecourse, BankstownBankstown Airport Airport AWS, AWS, Sydney Sydney Olympic Olympic Park Park AWS, AWS, and TerreyTerrey Hills Hills Reserve Reserve in in November November 2015– 2015– OctoberOctober 2016. 2016.

SinceTable CDD 2. Description is an important of the extended index weather reflecting stations the locationsclimate andand CDD energy calculations demand based of buildings, on data the analysisfrom is 2015extended to 2016. to calculate the cooling degree days of a larger region and compare CDD calculations for 24 different locations across the Sydney metropolitan area. Table 2 summarises the ◦ ◦ geographicalWeather location Station and LocationsCDDs of the extended Longitude weather ( E) Latitude stations ( S)based on Region data from CDD November 2015 to OctoberSydney 2016. (Observatory The spatial Hill) pattern of coolin 151.21g degree days 33.86 calculated On for the coast24 sites is 188 illustrated on the map (FigureSydney 3). The Airport results of such an invest 151.17igation foster 33.95 a better understanding On the coast of 227 the climate Canterbury Racecourse 151.11 33.91 Inland 199 and energy consumptionBankstown Airport of buildings AWS in different 150.99 climatic conditions. 33.92 It should Inland be noted 262 that the Degree Day.netSydney online Olympic tool Parkis programmed AWS to estima 151.07te CDD to 33.83account for missing Inland temperature 247 data [43]. Terrey Hills Reserve 151.23 33.69 Inland 126 Gymea Bay, South of Sydney 151.08 34.05 Inland 241 Horsley Park Equestrian Centre AWS 150.86 33.85 Inland 239 Table 2. DescriptionRichmond of Aus-Afb the extended weather stations 150.78 locations 33.60and CDD calculations Inland based294 on data from 2015 toPenrith 2016. Lakes AWS 150.68 33.72 Inland 310 Blacktown, Blacktown 150.89 33.77 Inland 443 Longitude Latitude WeatherCampbell Station Town (mount Locations Annan) 150.77 34.06Region Inland 232CDD Ross Street, Glenbrook 150.62(°E) (°S) 33.77 Inland 329 Sydney Colyton,(Observatory Colyton Hill) 151.21 150.79 33.86 33.79 On Inland the coast 468 188 Orchard Hills, Orchard Hills 150.74 33.79 Inland 563 KissingSydney Point Airport rd, Turramurra 151.17 151.13 33.95 33.74 On Inland the coast 232 227 CanterburyKoola Avenue, Racecourse Davidson 151.11 151.18 33.91 33.75 Inland 181 199 BankstownMerrylands Airport West AWS 150.99 150.97 33.92 33.84 Inland 425 262 Wildthorn Avenue, Dural 151.01 33.66 Inland 333 SydneyKentwell Olympic Street, Baulkham Park AWS Hills 151.07 150.99 33.83 33.76 Inland 282 247 TerreyCecil Hills Hills, Reserve Cecil Hills 151.23 150.85 33.69 33.89 Inland 422 126 GymeaLeppington, Bay, South Leppington of Sydney 151.08 150.82 34.05 33.95 Inland 343 241 Horsley ParkLusty Equestrian Street, Marrickville Centre AWS 150.86 151.15 33.85 33.93 Inland 245 239 Mascot, Mascot 151.19 33.93 Inland 307 Richmond Aus-Afb 150.78 33.60 Inland 294 Penrith Lakes AWS 150.68 33.72 Inland 310 Blacktown, Blacktown 150.89 33.77 Inland 443 Campbell Town (mount Annan) 150.77 34.06 Inland 232 Ross Street, Glenbrook 150.62 33.77 Inland 329 Colyton, Colyton 150.79 33.79 Inland 468 Sustainability 2017, 9, 712 18 of 21

Orchard Hills, Orchard Hills 150.74 33.79 Inland 563 Kissing Point rd, Turramurra 151.13 33.74 Inland 232 Koola Avenue, Davidson 151.18 33.75 Inland 181 Merrylands West 150.97 33.84 Inland 425 Wildthorn Avenue, Dural 151.01 33.66 Inland 333 Kentwell Street, Baulkham Hills 150.99 33.76 Inland 282 Cecil Hills, Cecil Hills 150.85 33.89 Inland 422 Leppington, Leppington 150.82 33.95 Inland 343 SustainabilityLusty2017, 9Street,, 712 Marrickville 151.15 33.93 Inland 24518 of 21 Mascot, Mascot 151.19 33.93 Inland 307

As depicteddepicted in in Table Table2, the2, resultingthe resulting cooling coolin degreeg degree days for days the extendedfor the extended weather stationweather locations station ◦ ◦ varylocations between vary126 betweenC day 126 and °C 563 dayC and day 563 in 2015–2016.°C day in 2015–2016. Figure 22 shows Figure that 22 theshows spatial that pattern the spatial and magnitudepattern and of magnitude CDD vary of from CDD location vary from to location. location A higherto location. CDD A was higher shown CDD in the was western shown Sydney in the suburbs,western Sydney with significant suburbs, with increasing significant trends increasing in inland trends areas in located inland 30–40 areas kmlocated west 30–40 of Sydney km west CBD. of ThisSydney finding CBD. shows This thatfinding during shows the lastthat 12during months the (November last 12 months 2015–October (November 2016), 2015–October western suburban 2016), areaswestern in Sydneysuburban have areas experienced in Sydney a morehave severeexperience climated a with more up severe to three climate times higherwith up CDDs to three compared times tohigher Northern CDDs and compared central partsto Northe of Sydney.rn and This central suggests parts that of significantSydney. This cooling suggests is required that significant for some inlandcooling locations, is required especially for some those inland located locations, in the westespecially of Sydney. those Thelocated observed in the spatial west of variation Sydney. of The the CDDsobserved is likely spatial explained variation by of topographic the CDDs is variables, likely explained urban form,by topographic and proximity variables, to ocean, urban lakes, form, forests, and andproximity grasslands. to ocean, lakes, forests, and grasslands.

Figure 22. 22. CDDsCDDs maps maps for for the theSydney Sydney areaarea considering considering data of data 24 stations of 24 stations in November in November 2015–October 2015– October2016. 2016.

8. Conclusions 8. Conclusions Half-hourly climate data from six meteorological stations located in the greater Sydney area Half-hourly climate data from six meteorological stations located in the greater Sydney area were were used to analyse the magnitude and the characteristics of the UHI in the city. The whole analysis used to analyse the magnitude and the characteristics of the UHI in the city. The whole analysis was was performed for the period 2005–2010. It was found that important temperature differences exist performed for the period 2005–2010. It was found that important temperature differences exist between between the eastern and western parts of the city. Both a strong UHI phenomenon and oasis the eastern and western parts of the city. Both a strong UHI phenomenon and oasis phenomenon were phenomenon were observed. The average maximum magnitude of the phenomena reached up to 6 observed. The average maximum magnitude of the phenomena reached up to 6 K. The patterns of the K. The patterns of the ambient temperature distribution in the city were found to depend highly on ambient temperature distribution in the city were found to depend highly on the synoptic climatic the synoptic climatic conditions and the strength of the advection flows. High intensities of the UHI conditions and the strength of the advection flows. High intensities of the UHI phenomenon were associated with the existence of a sea breeze in the eastern parts of the city, decreasing the temperature of the coastal zone, combined with westerly winds from the inland that heat up the western zones of the city. High intensities of the oasis phenomenon were associated with low wind speeds and a very weak development of the sea breeze in the coastal area. The important release of anthropogenic heat in the central and eastern parts of the city, combined with the reduced heat absorption in the western suburbs, intensified the magnitude of the oasis phenomenon. High UHI intensities were mainly observed during the warm summer period while the oasis phenomenon was stronger during the winter and the intermediate seasons. Sustainability 2017, 9, 712 19 of 21

Using data on the Cooling Degree Days calculated from 23 stations located in the greater Sydney area for the period 2014–2015, it was found that the development of the UHI in Western Sydney may have a very significant impact on the cooling energy consumption of buildings and also on indoor and outdoor comfort conditions. It is characteristic that the CDD in Western Sydney is almost three times higher than in the central and northern parts of the city. The whole analysis revealed the importance of local climate change and the UHI in coastal cities. Coastal urban zones that benefit from a sea breeze are more climate-resilient and are characterised by lower ambient temperatures than inland urban zones located quite far from the coast. The possible existence of an additional heating mechanism, like the advection of warm air from nearby spaces, may intensify the strength of the problem. Urban planning, considering the extension of coastal cities inland, should take into account the possible adverse climatic conditions and employ natural mitigation techniques able to dissipate the excess urban heat. The results of this study suggest that urban areas can significantly benefit from urban design and planning initiatives for heat reduction, e.g., by implementing bioclimatic urban design measures including increased vegetation and greenery, prevalence of shade, and reflective materials for roofs and pavement. Detailed investigation of these strategies is proposed for a subsequent paper. The use of advanced mitigation technologies is of importance in the reduction of adverse UHI-related health effects and the energy consumption of buildings.

Acknowledgments: The research has been financed and performed under the SJTU-UNSW Collaborative Research Fund—Seed Grant RG152786. Author Contributions: Mattheos Santamouris, Xiaoqiang Zhai, and Ruzhu Wang conceived and designed the experiment; Mattheos Santamouris, Shamila Haddad and Francesco Fiorito performed the experiments; Mattheos Santamouris and Shamila Haddad analyzed the data; Mattheos Santamouris and Shamila Haddad wrote the paper; Francesco Fiorito, Paul Osmond, Lan Ding, and Deo Prasad contributed material and contributed to the writing and editing of this paper. Conflicts of Interest: The authors declare no conflict of interest.

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