Adapting to sea-level rise
Observations of sea-level rise
Global average temperatures have warmed by over 0.7ºC over the last 100 years, as reported in the Intergovernmental Panel on Climate Change’s Fourth Assessment Report [Intergovernmental Panel on Climate Change website] on the science of climate change. The ocean is absorbing 80 per cent of the heat added to the climate system and average ocean temperatures have increased down to a depth of 3000m. This warming is causing an expansion of ocean water which, in combination with water from the melting of land-based ice, is causing sea-levels to rise. Consequently, sea-levels in New Zealand rose by 17 centimetres last century and they have risen on average 1.7 mm/year over the last 40 years.
During 1961-1993 global average sea level has risen at an average rate of 1.7 mm per year and during 1993 – 2003 average sea level rise was approximately 3.1 mm per year. It is possible that this is not a temporary increase in the rate of sea-level rise but may reflect a change to significantly higher trends.
The impacts of climate change on our coast
Much of New Zealand’s urban development and infrastructure is located in coastal areas, making it vulnerable to coastal hazards such as coastal erosion, inundation and sea-level rise.
The following changes are likely to occur as a result of climate change:
- coastal defences are overtopped by waves or high tides more often
- severe storms increase in intensity and storm surge levels rise
- some sandy beaches, like in the Manawatu, may continue to accrete, but more slowly
- some gravel beaches, like Haumoana in Hawke's Bay, are more likely to erode
- waves in Wellington could be 15 per cent higher by 2050 and 30 per cent higher by 2100
- areas with smaller tidal ranges, like Wellington, the Cook Strait area and the East Coast, may have bigger problems with the high tide mark exceeded more often.
Guidance on planning for future sea-level rise in New Zealand
It is important that we start planning for future sea-level rise now. Planning decisions on infrastructure made by councils and engineers often have consequences that extend over 50-100 years or more. Sea-level may rise significantly in this time.
The Ministry for the Environment provides a range of guidance materials and publications to help identify climate change impacts and adaptation responses. The publication "Preparing for Coastal Change" provides an overview of the impacts that climate change is expected to have on coastal hazards, not only through sea level rise but also through storm surge, wind and waves.
The Ministry recommends planning for the following projection of future sea-level rise:
- For planning and decision timeframes out to 2090–2099, a base value sea-level rise of 0.5m relative to the 1980–1999 average be used along with an assessment of potential consequences from a range of possible higher sea-level rise values. At the very least, all assessments should consider the consequences of a mean sea-level rise of at least 0.8m relative to the 1980–1999 average.
- For planning and decision timeframes beyond the end of this century an additional allowance of 10mm per year be used.
Central government response to planning for sea-level rise and increasing coastal risk
The New Zealand Coastal Policy Statement (NZCPS) 2010 [Department of Conservation website] provides further direction on planning for development in the coastal zone. The NZCPS 2010 was produced following a review of the previous NZCPS 1994, as required under the Resource Management Act.
Further information, including a copy of the Proposed NZCPS 2010, can be viewed on the website of the Department of Conservation:
- Independent Review of the New Zealand Coastal Policy Statement [Department of Conservation website]
- New Zealand Coastal Policy Statement [Department of Conservation website]
Local government response to planning for sea-level rise and increasing coastal risk
Most of local government has already started to plan for sea-level rise. Many councils have completed coastal hazard assessments, with maps showing areas expected to be affected over the next 50-100 years. Other activities being undertaken by local government include:
- restricting development in coastal erosion areas
- planning for managed retreat
- rejecting consents for alterations or extensions to existing buildings in the coastal zone
- discouraging the construction of defences such as sea walls.
Last updated: 8 September 2011
