Spatial modelling of sea level rise and extreme sea level exposure

Southland District Council is committed to understanding how climate change will impact our communities, and has commissioned Great South to prepare a report on spatial modelling of sea level rise.

The interpretation maps that are available to view through this website are provided as a graphic representation of the information in Great South’s report.

The Southland region wants to explore the future effects of climate change to be prepared and plan appropriately for the next steps. This technical report investigates one specific aspect of how climate change could affect our district, focusing on how climate change and sea level rise might intensify extreme sea level events up to 280 years in the future under selected case scenarios. The sea level rise projections encompass four different scenarios, for years 2090, 2130 and 2300, in accordance with the Ministry of the Environment’s (MfE) 2022 Interim Guidance on the use of new sea level rise projections.

The report centres on six specific locations on the south coast of the Southland district territorial authority: Colac Bay, Curio Bay,Fortrose, Oban, Riverton and Waikawa.
The projections have been supplied as geographic files and integrated into map viewers. The GNS Science peer review confirmed that the work is robust.

Extreme sea level means the maximum reach of sea water when a high spring tide and a coastal storm coincide. The term “Mean High Water Spring” (MHWS) describes the highest level that spring tides reach, on average, over a long timescale. The figure below illustrates the compounding impact of a high spring tide, storm surge and wind waves.

Extreme sea level events have historically occurred once every 100 years, but are projected to become an annual occurrence by 2050.

Due to the effects of sea level rise, in the future an extreme sea level event would lead to more flooding of low-lying coastal areas.

For instance, according to the report, in Riverton, an extreme sea level event in the present day would reach up to 3.36m. If the same event occurs in 100 years it is projected to reach 4.50m, an increase of 1.14m due to sea level rise.

13 December 2023

The Great South report and peer review were received by Council.

The Council meeting was recorded and can be viewed below. 

1 November 2023

Great South staff presented summary information about the modelling of sea level rise and extreme sea level exposure affecting parts of the Southland district to councillors in a workshop.

You can download the Powerpoint presentation here.

The Council workshop was recorded. It can be viewed on YouTube below.

The area of climate change induced sea level rise is a dynamic and changing area of science.

The report and spatial forecasting were prepared by Great South (Southland Regional Development Agency) for the Southland District Council with all reasonable skill and diligence based on the Ministry for the Environment’s 'Interim Guidance'. It is expected that the guidance will be updated as climate science knowledge is further refined, and an agreed rate of climate change is confirmed. Accordingly, the projections may change as updated climate science information becomes available. Users of this information are advised to seek independent qualified advice before making decisions based on this information.

These interpretation maps have been prepared to assist members of the public to understand the contents of the report using visual media.