The impacts and implications of climate change for the Clutha District Griffin, C. & Goldsmith, M., GHC Consulting Report 2020/03, April 2020 DISCLAIMER This report has been prepared by GHC Consulting Limited exclusively for and under contract to the Clutha District Council. Unless otherwise agreed in writing, GHC Consulting Limited accepts no responsibility for any use of, or reliance on any contents of this report by any person other than the Clutha District Council and shall not be liable to any person other than Clutha District Council, on any ground, for any loss, damage or expense arising from such use or reliance. BIBLIOGRAPHIC REFERENCE Griffin, C.E. & Goldsmith, M.J., 2020. The impacts and implications of climate change for the Clutha District, GHC Consulting Report 2020/03, April 2020. ACKNOWLEDGEMENTS The authors would like to thank the valuable GIS support provided by David Rowe at the Clutha District Council for producing the maps shown in this report. We would also like to acknowledge NIWA for openly sharing their climate projection and coastal flooding datasets with us. Without these datasets, this report would not have been possible. Finally, we would like to thank all of the local informants living in the Clutha District who so generously provided their time and knowledge. CONTENTS EXECUTIVE SUMMARY ............................................................................................. IX 1.0 INTRODUCTION ............................................................................................... 1 1.1 GEOGRAPHIC AREAS WITHIN THE CLUTHA DISTRICT ..................................... 1 1.2 AN OVERVIEW OF THE CLIMATE DATA SOURCED FOR THIS REPORT ............... 4 1.2.1 Local knowledge ...................................................................................... 4 1.2.2 Historic temperature and precipitation data ............................................ 4 1.2.3 Future temperature and precipitation models ......................................... 5 1.2.4 Extreme sea level .................................................................................... 6 1.2.5 Hydrological projections .......................................................................... 6 1.3 UNDERSTANDING EMISSIONS SCENARIOS ................................................... 7 1.4 CHAPTER 1 REFERENCES .......................................................................... 8 2.0 CLUTHA DISTRICT OVERVIEW ..................................................................... 10 2.1 TEMPERATURE PREDICTIONS ................................................................... 10 2.1.1 Mean annual air temperature ................................................................ 10 2.1.2 Temperature extremes .......................................................................... 12 2.1.3 Snow days ............................................................................................. 15 2.2 PRECIPITATION CHANGES ........................................................................ 15 2.2.1 Mean annual precipitation ..................................................................... 15 2.2.2 Number of heavy rain days ................................................................... 17 2.2.3 Magnitude of high intensity rainfall events ............................................ 17 2.2.4 Dry days ................................................................................................ 20 2.2.5 Extreme wind ......................................................................................... 20 2.3 OUR OCEAN ............................................................................................ 23 2.4 SUMMARY .............................................................................................. 25 2.5 CHAPTER 2 REFERENCES ........................................................................ 25 3.0 COASTAL AND EASTERN CLUTHA ............................................................. 27 3.1 INTRODUCTION ....................................................................................... 27 3.1.1 Key findings: .......................................................................................... 27 3.2 UNDERSTANDING THE PAST AND PRESENT CLIMATE .................................. 28 3.2.1 Air temperature ...................................................................................... 29 3.2.2 Rainfall ................................................................................................... 30 3.3 WHAT DO FUTURE CLIMATE PREDICTIONS TELL US? ................................... 33 3.3.1. Air temperature ...................................................................................... 33 3.3.2. Rainfall ................................................................................................... 34 3.3.3. Other atmospheric changes .................................................................. 34 3.4 CLIMATE CHANGE IMPLICATIONS FOR PEOPLE, INFRASTRUCTURE AND INDUSTRY IN COASTAL AND EASTERN CLUTHA ........................................... 35 3.4.1 Changes in flood risk ............................................................................. 35 3.4.2 Hazards faced by low-lying coastal settlements ................................... 39 3.4.3 Agriculture ............................................................................................. 46 Clutha District Climate Change Impacts Report i 3.4.4 Forestry ................................................................................................. 47 3.5 SUMMARY: WHERE TO FROM HERE? ......................................................... 47 3.6 CHAPTER 3 REFERENCES ........................................................................ 48 4.0 THE CATLINS ................................................................................................. 50 4.1 INTRODUCTION ....................................................................................... 50 4.1.1 Key findings: .......................................................................................... 50 4.2 UNDERSTANDING THE PAST AND PRESENT CLIMATE .................................. 51 4.2.1 Air temperature ...................................................................................... 51 4.2.2 Rainfall ................................................................................................... 52 4.3 WHAT DO FUTURE CLIMATE PREDICTIONS TELL US? ................................... 54 4.3.1 Air temperature ...................................................................................... 55 4.3.2 Rainfall ................................................................................................... 55 4.3.3 Other atmospheric changes .................................................................. 55 4.4 CLIMATE CHANGE IMPLICATIONS FOR PEOPLE, INFRASTRUCTURE AND INDUSTRY IN THE CATLINS ....................................................................... 56 4.4.1 Hazards faced by low-lying coastal settlements ................................... 56 4.4.2 Tourism .................................................................................................. 65 4.4.3 Wildlife ................................................................................................... 65 4.4.4 Agriculture ............................................................................................. 66 4.4.5 Forestry ................................................................................................. 66 4.5 SUMMARY: WHERE TO FROM HERE? ......................................................... 67 4.6 CHAPTER 4 REFERENCES ........................................................................ 67 5.0 CENTRAL CLUTHA ........................................................................................ 70 5.1 INTRODUCTION ....................................................................................... 70 5.1.1 Key findings: .......................................................................................... 70 5.2 UNDERSTANDING THE PAST AND PRESENT CLIMATE .................................. 71 5.2.1 Air temperature ...................................................................................... 72 5.2.2 Rainfall ................................................................................................... 73 5.3 WHAT DO FUTURE CLIMATE PREDICTIONS TELL US? ................................... 74 5.3.1 Air temperature ...................................................................................... 74 5.3.2 Rainfall ................................................................................................... 75 5.3.3 Wind speed and direction ...................................................................... 75 5.4 CLIMATE CHANGE IMPLICATIONS FOR PEOPLE, INFRASTRUCTURE AND INDUSTRY IN CENTRAL CLUTHA ................................................................ 75 5.4.1 Changes in flood risk ............................................................................. 76 5.4.2 Agriculture ............................................................................................. 79 5.4.3 Forestry ................................................................................................. 79 5.5 SUMMARY: WHERE TO FROM HERE? ......................................................... 80 5.6 CHAPTER 5 REFERENCES ........................................................................ 80 6.0 WEST OTAGO ...............................................................................................