Meteorological Hazards and the Potential Impacts of Climate Change in Wellington Region A Scoping Study 21 June 2002 This report has been specially prepared for the Wellington Regional Council. Andrew Tait, Rob Bell, Stuart Burgess, Richard Gorman, Warren Gray, Howard Larsen, Brett Mullan, Steve Reid, John Sansom, Craig Thompson and David Wratt National Institute of Water and Atmospheric Research Ltd PO Box 14-901, Kilbirnie, Wellington. and Mike Harkness Wellington Regional Council Regional Council Centre, 142-146 Wakefield Street, Wellington. NIWA Client Report WLG2002/19 WRC Pub. No. WRC/RP-T-02/16 Wellington Regional Council Meteorological Hazards and Climate Change Report, June 2002 2 Notice of Copyright: The copyright for this report is held by the Wellington Regional Council. The copyright for individual figures and tables contained in this report is indicated on these figures and tables. Where there is a copyright statement on individual figures and tables, they may be used for Civil Defence and Emergency Management purposes, provided appropriate acknowledgement is made, but may not be reproduced for other purposes without the prior consent of the copyright holder. Disclaimer: NIWA and WRC staff have used the best available information in preparing this report, exercising all reasonable skill and care. Nevertheless, NIWA and WRC accept no liability, whether direct, indirect or consequential, arising out of the provision of this information. Reviewed by: …………………………………… Released by: …………………………………… Wellington Regional Council Meteorological Hazards and Climate Change Report, June 2002 3 Contents Contents .........................................................................................................................3 List of Figures................................................................................................................6 List of Tables .................................................................................................................8 Executive Summary.......................................................................................................9 1. Introduction..............................................................................................................12 1.1 The Climate of The Wellington Region.............................................................12 1.2 Overview of Meteorological Hazards in the Wellington Region ......................16 1.2.1 Floods......................................................................................................16 1.2.2 Droughts..................................................................................................17 1.2.3 Landslides and Erosion...........................................................................17 1.2.4 Coastal Flooding .....................................................................................18 1.2.5 Severe Winds ..........................................................................................19 1.2.6 Snow and Frost .......................................................................................19 1.2.7 Excessive Temperature ...........................................................................20 1.2.8 Lightning and Hail ..................................................................................20 1.2.9 Ex-Tropical Cyclones .............................................................................21 1.2.10 Wildfire.................................................................................................21 1.3 Overview of Climate Change Impacts in the Wellington Region .....................22 1.3.1 Climate Change Impacts on Specific Meteorological Hazards ..............23 1.3.2 Impacts of Climate Change on the Wellington Region ..........................25 1.4 Information Needs of Key Stakeholders............................................................27 1.5 Bibliography ......................................................................................................28 2. Floods.......................................................................................................................30 2.1 An Historical High Rain Event: 27-28 October, 1998.......................................30 2.1.1 Description of the weather......................................................................30 2.1.2 Storm return period 27-28 October.........................................................31 2.1.3 Damage ...................................................................................................32 2.1.4 Photos......................................................................................................32 2.2 Rainfall Return Period Maps .............................................................................32 2.3 The 100-Year Flood maps .................................................................................34 2.4 Knowledge Gaps................................................................................................37 2.5 High Risk Areas.................................................................................................37 2.6 Amelioration Methods .......................................................................................39 2.6.1 Structural Methods..................................................................................39 2.6.2 Non-Structural Methods..........................................................................39 2.7 Bibliography ......................................................................................................40 3. Droughts...................................................................................................................42 3.1 An Historical Drought Period: Summer–Autumn 2000/01 ...............................43 3.1.1 A month-by-month chronology of the drought.......................................43 3.1.2 Some consequences and effects of the drought ......................................47 3.1.3 How the drought occurred and why it persisted .....................................48 3.1.4 How unusual was the summer–autumn 2000/01 drought?.....................48 3.2 High Risk Areas.................................................................................................50 3.3 Amelioration Methods .......................................................................................50 3.4 Knowledge Gaps................................................................................................51 3.5 Bibliography ......................................................................................................52 Wellington Regional Council Meteorological Hazards and Climate Change Report, June 2002 4 4. Landslides and Erosion............................................................................................53 4.1 Historical Landslide Events ...............................................................................53 4.1.1 December 1976 .......................................................................................53 4.1.2 1974.........................................................................................................58 4.1.3 1985.........................................................................................................59 4.2 High Risk Areas.................................................................................................61 4.3 Amelioration Methods .......................................................................................62 4.4 Knowledge Gaps................................................................................................62 4.5 Bibliography ......................................................................................................63 5. Coastal Flooding and Erosion..................................................................................65 5.1 Coastal Flooding ................................................................................................66 5.1.1 High tides................................................................................................67 5.1.2 Atmospheric pressure..............................................................................70 5.1.3 Storm surge .............................................................................................71 5.1.4 Waves......................................................................................................75 5.2 Coastal Erosion ..................................................................................................79 5.2.1 Risk of Coastal Erosion ..........................................................................82 5.3 Knowledge Gaps................................................................................................82 5.4 Vulnerable Areas ...............................................................................................83 5.5 Amelioration Methods .......................................................................................83 5.6 Bibliography ......................................................................................................84 6. Severe Winds ...........................................................................................................87 6.1 Weather situations causing high winds..............................................................87 6.2 Maps of extreme winds......................................................................................88 6.3 Extreme Winds Knowledge Gaps......................................................................91