Watch: Sea-level rise and subsidence a double hit for coastal areas

A new graphic visualisation shows the future faced by coastal settlements as climate change takes hold, especially for those that are also suffering from subsidence.

The most at risk areas - as shown in the video above - will have to contend with regular flooding when extreme weather hits.

Scientists have particular concerns for the future of seaside suburbs in Lower Hutt, as tectonic plate movements effectively double the rate of sea level rise.

Research by GNS Science and Te Herenga Waka estimates the shorelines of coastal suburbs such as Eastbourne and Petone are sinking at rates of 3mm to 4mm per year.

"That effectively doubles the amount of sea level rise and the rate of sea level rise," climate scientist Professor Tim Naish said.

As average global temperatures rise, coastal flooding events are also expected to rapidly increase.

"That road to Eastbourne and the Petone foreshore will be experiencing the historic flood, the flood we get every hundred years, the big coastal flood - will be an annual event. It will happen every year. Just with 30cm of sea level rise, and that's baked in.

"We can't avoid that, that is already baked into the ocean from the heat that's gone into the ocean, the melting of the ice sheets. We can no longer reverse that, so that's what we call 'committed climate change'."

He added: "The best we can hope for globally is 30cm of sea level rise by about 2060, and about 60cm of sea level rise by the end of the century."

But those thresholds are expected to be met faster in parts of New Zealand that are subsiding - so much so that sea level rise could reach 91cm by the end of the century in our most vulnerable areas, according to the NZ SeaRise research programme.

A report commissioned by the Greater Wellington Regional Council, published this year, states that in Lower Hutt alone, 4960 buildings are at risk of coastal flooding.

Residents are seeing the impacts, with insurance rejections, and hikes in premiums.

Greater Wellington natural hazard analyst Dr Iain Dawe told 1News: "We have one of the largest insurance uptakes in any country in the world, and we have probably in the past relied quite heavily on hoping that insurance is always going to cover us. But they're [insurance companies] looking quite closely and whether they can afford to carry on doing that in the future."

He added: "These are always challenging conversations. This is big scary stuff we're dealing with. And I completely understand that, if your property is going to be affected, there is a natural fear that you'll have as to what might be changing in terms of the policy, the planning, the insurance.

"These are big gnarly issues that we all have to deal with, but the fact of the matter is, that we're starting to see impacts on our infrastructure."

Some Petone residents were more optimistic about the future of the neighbourhood they love.

Douglas O'Halloran said the location "encourages you to get outside and go walking, it's a nice spot".

Insurance had become harder for him though: "I bought a building probably about five or six years ago on the Esplanade and in the process of buying it I got refused insurance. That's the price you pay for living here."

Overall, however, he said: "I'm not concerned directly about the sea level rise, I'm more concerned about institutions' reaction to it."

Fellow resident Jason Brown also spoke highly of living in Petone: "It's great here. It's beautiful. It's nice and central."

When asked if sea level rise was a major concern, Brown said: "Not short term anyway - I don't think the impact will be that great."

But he was also noticing insurance changes: "We own commercial and residential property in Petone so, it's certainly affecting us."

Tens of millions of dollars are being spent on new seawalls to protect coastal routes on either side of Petone, along State Highway 2 to Ngāūranga and on the road to Eastbourne.

Dawe also said that at Petone: "There's quite a lot of sediment and it's quite a wide sandy beach. So there's quite a lot of natural ecosystem that will provide a defence mechanism against coastal erosion and inundation."

He said another major problem in Lower Hutt was sea level rise interacting with groundwater - and the Hutt River.

"So there's the big Riverlink project that's looking to upgrade the stop banks in Lower Hutt as well. So there's a combination between fluvial or river, and coastal flooding, affecting that area."

New Zealand climate scientists have called upon central and local governments to act urgently in response to sea level rise.

Some options include expanding wetlands, extending mangrove plantations, as well as man-made measures.

Naish said: "I suspect for most locations around New Zealand, it will be a combination of protection by seawall and a combination of ultimately moving communities - and most importantly not putting your development in dangerous places."

The Government this month released its climate change strategy, which Climate Change Minister Simon Watts said had five pillars:

But Labour Climate Change spokesperson Megan Woods has said that if Watts believed his plan was comprehensive or ambitious then "New Zealand is in real trouble".

"This three-page document is flimsy and backward-looking. I can’t help but wonder if the Government is scrambling to get ahead of the Climate Commission’s report card on emission reductions that is due in the coming days," she said last week.