Higher sea-level calculations push more of Wellington under water

Thursday, 1 August 2019

Wellington City Council has unofficially ditched an optimistic sea-level rise scenario in favour of one that could see much of the central city and low-lying suburbs under water.

It comes as a yet-to-be-released vulnerability assessment has been commissioned by Wellington's councils, outside Wellington city, looking at how sea-level rise will affect the entire region.

But Wellington City Council - itself expected to suffer billions of dollars worth of damage and thousands of people displaced - commissioned its own report in 2013 which had a best-case scenario of 0.6 metres of sea-level rise this century.

A 2013 WCC report highlighted the inundation areas, in yellow, for Wellington under 1.5 metres of sea-level rise.

It can now be confirmed the council has all-but ditched that optimistic figure in favour of about 1.5m leading to an exponentially-different outcome as the best-case.

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Wellington City Councillor David Lee says the new level of sea level change is now closer to 1.5 metres.

Under the new scenario, also outlined in the 2013 report, areas in line for 'inundation' include much of the area around Westpac stadium, swathes through the central city, as well as lower parts of Oriental Bay, Evans Bay, Kilbirnie, Shelly Bay, Seatoun, and the South Coast bays.

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It will mean that without massive mitigation measures - as extreme as reclaiming Wellington harbour east of a line between Freyberg Pool and CentrePort - the Harbour Quays will be in the inundation zone. It is here Wellington's $6.4 billion Let's Get Wellington Moving has its preferred route for mass-transit.

Wellington City Councillor Iona Pannett has confirmed the old best-case level of 0.6 metres of sea-level change in Wellington is now essentially ditched.

The old best-case scenario was almost-entirely limited to areas immediately beside the sea.

A regional council sea-level change calculator shows the new best-case scenario would put parts of Petone, Waiwhetu and the eastern bays in the likely inundation zone, as well as much of low-lying Makara Beach, Pauatahanui, and Kapiti.

Victoria University Wellington climate scientist James Renwick said about 30 centimetres of sea-level rise by 2050 to 2060 was now all-but certain and all else from there depended on a global reduction in burning fossil fuels.

He estimated that, without a massive change in world events, a 1.5m rise was looking very plausible though it was impossible to give it an exact timeframe.

Wellington City councillors Iona Pannett and David Lee have confirmed to Stuff that the 0.6m scenario was now all-but dead.

Lee, who has the climate change portfolio, confirmed the new, unofficial figure was closer to 1.5m and there were three key mitigation solutions as water met homes.

There was rate or taxpayer funded ones such as sea walls or people personally adapting their homes to deal with water, notably when it came in with storm surges. But the least-palatable was people simply ditching their homes.

He believed the council needed to change the district plan and land information memorandums (Lims) to reflect the new, accepted level.

The 2013 report estimated the cost to Wellington, comparing 0.6m rise to 1.5m, would see the cost of assets affected rise from $400 million to $6.5 billion, while the number of residents displaced would grow from about 150 to about 2000. Lee said those figures were now optimistic.

Storm surges, expected more under climate change, could push the levels much higher.

Makara Beach, where a storm surge with ex-Cyclone Gita in 2018 met waters from the rain, saw flooding kilometres inland. Those kind of cases could become common place, Lee said.

Pannett, with the infrastructure and sustainability portfolio, said the Ministry for Environment estimated a 1 to 1.4m rise. She believed the council needed to be prepared for higher.

To see the level of sea rise the council has produced a sea-level rise map.