28 Feb 2023

Many flood-damaged homes should not be rebuilt, says climate risk expert

5:35 am on 28 February 2023
Esk Valley on 20 February following Cyclone Gabrielle.

Esk Valley on 20 February following Cyclone Gabrielle. Photo: RNZ/ Nick Monro

Many homes devastated by floodwater and silt should not be rebuilt as they will almost certainly be affected again, says a climate risk expert.

The Esk Valley has been particularly hard hit by the cyclone.

Orchardist Paul Paynter has 45 hectares - about the size of 45 rugby fields - buried under more than a metre of silt.

"I wouldn't put any significant assets in that valley again without either some flood protection, or the rapid onset of insanity."

There was so much silt he was not sure if it was possible for it to all be removed, or if it was a good idea.

"What the river silt tends to do is build river terraces. And over time, given a generation or two, they turn into very nice free draining fertile soils.

"And those terraces move their way up above the river - the taller the river terrace, the less likely you are to flood next time."

'It doesn't make a lot of sense [to] … rebuild' in some places

Work to assess the damage and next steps for the places worst affected by the cyclone and recent weather bombs is still being done.

The aftermath of massive flooding that swept through the Esk Valley during Cyclone Gabrielle. The river's normal path can be seen running down the right of the valley.

The aftermath of massive flooding that swept through the Esk Valley during Cyclone Gabrielle. Photo: RNZ/ Sally Murphy

Climate change makes the storms more damaging, and more likely.

Climate Sigma climate economist and modeller Belinda Storey said homes in floodplains that were inundated regularly, or quickly, would likely keep getting struck again and again unless expensive protections were built.

"If a house has been devastated in these events, then it doesn't make a lot of sense for us to rebuild that house."

While it was understandable to want to rush to help people rebuild after a crisis, in the long run it could make things worse because it encouraged people to remain in harm's way, Storey said.

Pay for mapping or let flooding reveal the risky places

Laser topographical mapping - called LiDAR - gave details down to the centimetre and could be used to help accurately plot flood risk, Storey said.

Gaps and coverage of laser topographical mapping in New Zealand as of 2022.

Belinda Storey says ideally the map should be all green. Photo: Land Information New Zealand

It had been done extensively in Te Tai Rāwhiti , but in Hawke's Bay it was a different story, she said.

"We currently have better understanding of the topography of the moon than we do of Hawke's Bay."

Storey said it was far cheaper to invest in nationwide laser mapping, than pay for it by letting nature reveal the places most vulnerable to flooding after the next inevitable weather bomb.

National conversation needed on fair compensation for those who must leave

Victoria University Emeritus Professor of public policy Jonathan Boston said tens of thousands of people might need to move out of harm's way by the end of the century.

He warned there were no easy answers but there needed to be a national conversation, and cross-party consensus, about the fairest way to split costs.

Flood damage in the Esk Valley in Hawke’s Bay.

Flood damage in the Esk Valley in Hawke's Bay after Cyclone Gabrielle. Photo: RNZ / Tess Brunton

"I appreciate this is very, very difficult for people have to come to terms with, but we must," Boston said.

"For many people in the last year or so in New Zealand … climate change has arrived, and it's been devastating, and we need to take that really seriously."

Victoria University economics of disasters and climate change chair professor Ilan Noy said any compensation package needed to be structured to dissuade holdouts.

"You [could] end up with the … worst of all possible worlds where … because some people decided to stay, you still need to try and protect the communities … provide them the services: water and electricity and so forth, but it's a much-diminished community."

Noy said insurers needed to allow homeowners to take payouts and rebuild elsewhere out of harm's way.

Cyclone Recovery Minister Grant Robertson is already indicating some devastated areas may not be rebuilt, with a decision to be made possibly within a month.

Meanwhile, the government is part way through creating a nationwide plan for managed retreat, with decisions from Cabinet due later in the year.

Democracy could be undermined by poor policy choices - Boston

An NH90 helicopter and crew recover people from the rooftops of their homes in Esk Valley, Napier.

People had to be rescued from rooftops in Esk Valley after torrential rain from Cyclone Gabrielle caused severe flooding. Photo: Supplied / NZDF

Boston said with the danger of sea level rise also looming, countries faced unprecedented challenges, and durable plans on how to respond were needed.

"If we don't have them, we will flounder," he said.

"We will run the risk of undermining public confidence in our democratic institutions, potentially with profound implications for the future of democracy."

He recently co-wrote a paper on managed retreat for the Environmental Defence Society.

Central government would need to provide a substantial part of any compensatory package, Boston said.

He believed the government should negotiate to purchase the properties of those affected, with a cap on the total amount that any particular property owner could receive.

People's principle home should get greater compensation than baches or rentals, he said.

"These are detailed matters that really need to be thought about very carefully, because almost anything you do is going to have both positive and negative implications.

"And whatever [the government] might propose … [for] pre-emptive managed retreat, there are going to be serious problems.

"There's no right solution here, no easy fix."

He said another fishhook was that pre-emptive moves also could be far more expensive as insurers would not be kicking in for that.

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