New Zealand Fluvial and Pluvial Flood Exposure Prepared for The Deep South Challenge Prepared by: Ryan Paulik Heather Craig Daniel Collins For any information regarding this report please contact: Ryan Paulik Hazard Analyst Meteorology and Remote Sensing +64-4-386 0601 [email protected] National Institute of Water & Atmospheric Research Ltd Private Bag 14901 Kilbirnie Wellington 6241 Phone +64 4 386 0300 NIWA CLIENT REPORT No: 2019118WN Report date: June 2019 NIWA Project: DEPSI18301 Quality Assurance Statement Reviewed by: Dr Emily Lane Formatting checked by: Patricia Rangel Approved for release by: Dr Andrew Laing © All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system. Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client. Contents Executive summary ............................................................................................................. 6 1 Introduction .............................................................................................................. 9 2 Methods .................................................................................................................... 9 2.1 Flood Hazard Area Mapping ..................................................................................... 9 2.2 Elements at risk ....................................................................................................... 17 2.3 Linking flood hazard exposure with climate change .............................................. 21 2.4 Methodological limitations ..................................................................................... 21 3 Results .................................................................................................................... 25 3.1 Results Summary .................................................................................................... 25 3.2 Population ............................................................................................................... 25 3.3 Buildings .................................................................................................................. 26 3.4 Transport infrastructure ......................................................................................... 34 3.5 Electricity infrastructure ......................................................................................... 36 3.6 Three-waters infrastructure ................................................................................... 38 3.7 Land cover ............................................................................................................... 40 3.8 Mean annual flood response to regional climate change projections ................... 42 4 Conclusions and Recommendations ......................................................................... 49 4.1 Conclusions ............................................................................................................. 49 4.2 Recommendations for future national-scale exposure assessments ..................... 50 5 Acknowledgements ................................................................................................. 52 6 Glossary of abbreviations and terms ........................................................................ 55 7 References ............................................................................................................... 56 Appendix A Digital Appendix Contents ................................................................ 57 Tables Table 1-1: National and regional level exposure of elements at risk within identified New Zealand flood hazard areas. 8 Table 2-1: Classifications for ‘Flood Soil Layer, Flood Return Interval’ map (Webb and Wilson, 1995). 17 Table 2-2: Building use categories reported for this study. 19 New Zealand Fluvial and Pluvial Flood Exposure Table 2-3: Three-waters infrastructure node component types reported in this study. 20 Table 2-4: Land Cover Database Version 4.1 classes and land cover types reported in this study. 20 Table 3-1: New Zealand building and replacement value exposure identified in the FLHA. 27 Table 3-2: Regional level FLHA usually-resident population totals identified in catchments experiencing MAF change for scenario RCP 2.6. 43 Table 3-3: Regional level FLHA usually-resident population totals identified in catchments experiencing MAF change for scenario RCP 8.5. 43 Table 3-4: Regional level FLHA building totals identified in catchments experiencing MAF change for scenario RCP 2.6. 44 Table 3-5: Regional level FLHA building totals identified in catchments experiencing MAF change for scenario RCP 8.5. 45 Table 3-6: Regional level FLHA building replacement value (NZD$ 2016 millions) totals identified in catchments experiencing MAF change for scenario RCP 2.6. 45 Table 3-7: Regional level FLHA building replacement value (NZD$ 2016 millions) totals identified in catchments experiencing MAF change for scenario RCP 8.5. 46 Figure 2-1: North Island modelled and historic flood hazard maps available from local government. 11 Figure 2-2: South Island modelled and historic flood hazard maps available from local government. 12 Figure 2-3: North Island Flood Soil Layer Flood Return Interval (Ratings 2 to 6) map. 13 Figure 2-4: South Island Flood Soil Layer Flood Return Interval (Ratings 2 to 6) map. 14 Figure 2-5: North Island Flood Hazard Area (FLHA) map. 15 Figure 2-6: South Island Flood Hazard Area (FLHA) map. 16 Figure 2-7: Median percentage changes in mean annual flood flow (Collins and Zammit, 2016). 24 Figure 3-1: Region level 2013 usually-resident population exposure identified in the FLHA. 26 Figure 3-2: Region level residential building (a) and replacement value ($NZD 2016) (b) exposure in the FLHA. 28 Figure 3-3: Region level commercial building (a) and replacement value ($NZD 2016) (b) exposure in the FLHA. 29 Figure 3-4: Region level industrial building (a) and replacement value ($NZD 2016) (b) exposure in the FLHA. 30 Figure 3-5: Region level critical building (a) and replacement value ($NZD 2016) (b) exposure in the FLHA. 31 Figure 3-6: Region level community building (a) and replacement value ($NZD 2016) (b) exposure in the FLHA. 32 Figure 3-7: Region level ‘other’ building (a) and replacement value ($NZD 2016) (b) exposure in the FLHA. 33 Figure 3-8: Region level road network exposure in the FLHA. 34 Figure 3-9: Region level railway network exposure in the FLHA. 35 Figure 3-10: Region level airport exposure in the FLHA. 35 Figure 3-11: Region level national electricity grid transmission line exposure in the FLHA. 36 Figure 3-12: Region level national electricity grid structure exposure in the FLHA. 37 Figure 3-13: Region level national electricity grid site exposure in the FLHA. 37 New Zealand Fluvial and Pluvial Flood Exposure Figure 3-14: Region level three-waters network pipeline (km) exposure in the FLHA. Note: for this study, limited three-waters network pipeline data was available for Marlborough region. 39 Figure 3-15: Region level three-waters network node exposure in the FLHA map. Note: for this study, three-waters network node data was not available for Canterbury region, while limited data was available for Marlborough region. 39 Figure 3-16: Region level built land exposure in the FLHA map. 41 Figure 3-17: Region level production land exposure in the FLHA map. 41 Figure 3-18: Region level natural or undeveloped land exposure in the FLHA map. 42 New Zealand Fluvial and Pluvial Flood Exposure Executive summary This study is a first attempt to enumerate New Zealand’s populations and asset exposure in fluvial and pluvial floodplains. ▪ A national and consistent flood hazard map for New Zealand is absent at an appropriate resolution for identifying populations and assets in fluvial and pluvial floodplains. In the absence of a national flood hazard map, exposed areas are identified by creating a ‘composite’ flood hazard area map (FLHA) from modelled and historic flood hazard maps and flood prone soil maps, publicly available in August 2018. The map represents known or mapped floodplains and was deemed sufficient for a first attempt at enumerating national, region and territory level population and asset exposure. ▪ This report uses the term “elements at risk” to include: population, buildings (number and 2016 NZD replacement value), transport infrastructure (roads, railways, airports), electricity infrastructure (transmission lines, structures, sites), three-waters infrastructure (nodes, pipelines), and land cover (built, production, natural or undeveloped). These elements at risk provide a representative sample of built assets and land cover types exposed within New Zealand’s fluvial and pluvial floodplains. Elements at risk were identified on land within the FLHA. An overview of elements at risk in the FLHA are presented national and regional levels in Table 1-1. ▪ The highest regional level population and built asset exposure occurs in populous