The Tidal Inundation & Sea Level Rise dataset maps the extent of sea water coverage expected around the Auckland Region in the future with sea level rise during high tides alone. These water levels are based on The Mean High Water Spring Tide Sea Levels + 0.5m increments of sea level rise. The Mean High Water Spring Tide Sea Levels are the elevation of the high tide that is equalled or exceeded by only the highest 10% of all high tides.

These high tide levels include the astronomically driven tide only (due to rotational and gravitational effects) and do not include waves or storm surges (which are the rise in sea level caused by wind action and low barometric pressure related to storm events). The extent of storm-tide inundation will be greater and this is mapped in the Coastal Storm Inundation Hazard data layer. Rainfall and freshwater flooding are also not included in this data, but are available separately in other geomaps layers e.g. ‘Flood Plains’, or on the Auckland Flood Viewer).

The mean high water spring tide sea levels have been updated based on the mean sea level averaged over the period 2001–2019. This accounts for sea level rise that has occurred up until the effective base date of 2010, but does not include sea level rise that has occurred since that period. This is set out in the report Coastal inundation from sea-level rise in the Auckland Region (NIWA, 2023). 0.5m sea level rise increments are added on top of this in order to assess the increasing coastal inundation hazard into the future.

Sea-level rise values applied currently align with the projections by the Intergovernmental Panel on Climate Change sixth assessment report (2021), and the Ministry for the Environment (2022) Interim guidance on the use of new sea-level rise projections, which updates the Ministry for the Environment Coastal Hazards and Climate Change Guidance for Local Government (2017).

In MfE’s (2022) interim guidance, (excluding vertical land movement) one metre sea-level rise is projected to occur between 2095 - >2200, depending on the emission scenario used. Two metre sea-level rise is projected to occur in the longer term (beyond 2150).

MfE’s (2022) Interim guidance recommends the inclusion of vertical land movement (VLM) in relative sea level rise considerations. These are not included in the above sea level rise predictions due to the high VLM variability across the region. Vertical land movement is generally predicted to increase the rates of relative sea level rise for the Auckland region so should also be incorporated in planning and design.

Refer to Interim guidance on the use of new sea-level rise projections | Ministry for the Environmentand NZ Sea Risefor more information on MfE’s interim guidance on sea level rise and vertical land movement.

Mean high water spring tides are used to define the Coastal Marine area boundary within Auckland’s Unitary Plan. The inundation mapping is based on the Digital Elevation Model ground levels surveyed by aerial LiDAR between 2016-2018.

Lineage:

Coastal inundation from sea-level rise in the Auckland Region (NIWA, 2023)

(Note: The studies informing this mapping of coastal inundation generally used Auckland Vertical Datum 1946. Auckland Council is now transitioning to using New Zealand Vertical Datum 2016.)

Update Cycle:

Adhoc when improved data becomes available.

This data is available to the public on the Geomaps viewer and on Auckland Council Open Data portaland some coastal flood mapping is copied into LIM reports.