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Aotearoa New Zealand 1% AEP extreme sea level flooding map
Coastal flooding is a global hazard that also impacts Aotearoa New Zealand. Rising sea level is already causing more frequent flooding along many coasts and will greatly increase the frequency and consequences of flooding in future.
Decisions about how we adapt to sea-level rise require information about our exposure to coastal flooding, both now and in the future after a period of rising sea levels.
These maps and data provide a modelled representation of New Zealand’s 1% annual exceedance probability (AEP) extreme sea level flooding under current climatic sea conditions, plus relative sea level rise up to 2 m above present-day mean sea level. 1% AEP is equivalent to a 100-year return period a large (and currently rare) event with a small chance of happening in any given – year. The Aotearoa-New Zealand 1% AEP extreme sea level flooding map dataset comprises 21 coastal flooding scenarios representing relative sea-level rise ranging from 0 to 2m in 10cm (0.1m) increments.
The main purpose of the Aotearoa-New Zealand 1% AEP extreme sea level flooding map dataset is to identify national and regional level flood hazard and exposure trends with rising sea levels. It was not designed for hazard and exposure analysis at higher resolutions (e.g., property level)—many Councils have created high-resolution maps of coastal flooding exposure for this purpose.
The data is based on analysis of sea-level measurements and numerical models and was verified against sea-level runup observations collected after large storm-tide events. Flooding was mapped using a static (‘bathtub’) methodology. Nationwide coverage for low-lying coastal land was achieved using a composite topographical dataset comprised of Airborne Light Detection and Ranging (LIDAR) and bias corrected Shuttle Radar Topography Mission (SRTM), as described in this research paper.
The coastal flood maps have been used to describe New Zealand’s exposure to coastal flooding in several research reports and papers: Paulik et al. (2019, 2020, 2021, 2023).
In 2022 the NZ SeaRise project published projections of sea-level rise for Aotearoa that are complementary to the data linked from this page. See here for Ministry for the Environment guidance on using these datasets together. Further information about this tool is provided in the accompanying technical report: Coastal flood mapping methodology report.
Reference: Extreme coastal flood maps for Aotearoa New Zealand
More coastal flooding information is available
In addition to the 1% AEP scenario provided here, NIWA has also mapped 39, 18, 10, 5, 2, 1, 0.5, 0.2 and 0.1% AEP scenarios (equivalent to return periods of 2, 5, 10, 20, 50, 100, 200, 500 and 1000-years). All of these scenarios have additional relative sea-level rise increments added up to 2m above present-day mean sea level. GIS polygons of flooding extent and rasters of flooding depth are available.
These additional ARCGIS layers are available on request via license. Please email John-Mark.Woolley@niwa.co.nz.