Abstract
Coastal flooding from extreme sea levels will increase in frequency and magnitude as global climate change forces sea-level rise (SLR). Extreme sea-level events, rare in the recent past (i.e., once per century), are projected to occur at least once per year by 2050 along many of the world’s coastlines. Information showing where and how built-environment exposure increases with SLR, enables timely adaptation before damaging thresholds are reached. This study presents a first national-scale assessment of New Zealand’s built-environment exposure to future coastal flooding. We use an analytical risk model framework, “RiskScape”, to enumerate land, buildings and infrastructure exposed to a present and future 100-year extreme sea-level flood event (ESL100). We used high-resolution topographic data to assess incremental exposure to 0.1 m SLR increases. This approach detects variable rates in the potential magnitude and timing of future flood exposure in response to SLR over decadal scales. National built-land and asset exposure to ESL100 flooding doubles with less than 1 m SLR, indicating low-lying areas are likely to experience rapid exposure increases from modest increases in SLR expected within the next few decades. This highlights an urgent need for national and regional actions to anticipate and adaptively plan to reduce future socio-economic impacts arising from flood exposure to extreme sea-levels and SLR.
Highlights
Rising sea-levels in response to global climate change are expected to increase the frequency of coastal flooding from extreme sea-levels (ESLs) [1]
A nation-wide description of ESL100 elevations (Section 3.1) is followed by built-land and asset exposure to ESL100 flooding presented for the ‘first metre of sea-level rise (SLR)’ (Section 3.2), beyond the ‘first metre of SLR’ (Section 3.3) and ‘3 m SLR’ (Section 3.4)
This study presents a first national-scale assessment of New Zealand’s present and future built-environment exposure to coastal flooding from 100-year extreme sea-levels (ESL100) and SLR
Summary
Rising sea-levels in response to global climate change are expected to increase the frequency of coastal flooding from extreme sea-levels (ESLs) [1]. For built-environments, these flood regime changes will increase ‘nuisance’ flood exposure from smaller and more frequent flooding events [5], along with higher magnitude impacts from greater built-environment exposure to larger low frequency events. Various models and Representative Concentration Pathways (RCPs) estimate higher global mean sea-levels between 0.3 and 2 m by 2100 [8], threatening millions of people and USD trillions of built-assets from ESLs annually [9]. Rising sea-levels can eventually reach an adaptation threshold where coastal flood impacts exceed the tolerability or adaptive capacity of communities, governance arrangements, utility services or economies on low-lying coastal land. Decision-makers, in collaboration with communities, can proactively develop adaptive plans to manage social and economic impacts if they know the ESL and SLR increment where such ‘adaptation thresholds’ will emerge [3]
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