Sea level rise in Wellington

First recognition by Wellington's Dom Post that we might just have a problem.

Wellington sea level rising fastest 

in NZ

Matt Stewart

Stuff.

13/07/2012

Parts of coastal Wellington could be drowned if doomsday climate change predictions from a new study pan out over the next 100 years.

Two reports issued yesterday by Greater Wellington regional council show Wellington's sea level is the fastest rising in New Zealand - made worse by seismic rumblings causing the city to sink 1.7mm a year since 2000.

Worst-case scenarios coupling massive sea level rise with intense storm floods show low-lying coastal parts of the Eastbourne bays, Petone, Pauatahanui, as well as the river mouths at Otaki, Hutt, Whakataki (near Castlepoint), and Waikanae and the lower Wairarapa valley, could be forever swamped if sea levels rose 1.5m by 2115.

Paekakariki, Raumati South and Te Kopi would also be jeopardised by severe erosion.

"We're starting to see potentially severe impacts in those areas," Greater Wellington senior hazards analyst Iain Dawe said.

Downtown Wellington would be spared permanent inundation because the city's seawall would protect it from erosion, and its stormwater system would gradually drain the flood.

The harbour also protects the city because wave run-up - where swells slop over the foreshore in a storm - was not as pronounced in the CBD as in places such as the south coast.

The reports urge immediate action and aim to help urban planners make building, road and infrastructure development decisions in low-lying coastal areas.

"We need integrated coastal management in the region with authorities working together to plan for natural disasters in the future," Dr Dawe said.

The research was done by National Institute of Water and Atmospheric Research scientists.

The reports highlighted areas vulnerable to coastal flooding over the next 100 years.

Wellington Harbour had an average sea level rise of about 2mm a year over the past century. This was mainly due to climate change but was magnified by subsidence in the city over the past decade, caused by slow slips triggered by deep tectonic plate movements.

The region has "a more complicated spatial and temporal pattern of long- term relative sea level rise than other stable parts of New Zealand," the reports say.

Like land, the sea is not flat and has its own topography, which explains why Wellington could record a bigger rise than ports at Auckland, Dunedin and Christchurch. If the Wellington Fault ruptured, forecasts show Lower Hutt and Petone could subside by up to 1m.

Projections for century's end suggest the sea level in the Wellington region could rise by 0.8m by the 2090s or as high as 1.5m by 2115.

Storms could also get longer and stronger, increasing the likelihood of coastal flooding and erosion.