Tasman floods: The regions at risk from billions of dollars of damage

Flooding is projected to damage the homes of tens of thousands of Kiwis over the next 35 years, causing billions of dollars of damage.

Latest projections, prepared by Climate Sigma for the Ministry for the Environment, suggest already flood-ravaged Nelson and Tasman will be particularly hard-hit.

The report estimates almost 220,000 homes, worth almost $180 billion, are located within coastal inundation and inland flood zones.

More than a quarter of these are in Canterbury, with Tasman, Gisborne, West Coast and Nelson regions also having a higher proportion of vulnerable homes.

Up to 14,500 of these homes – with a combined value of $12.9 billion – are expected to be damaged by at least one extreme flooding event in the next 35 years.

On a per capita basis, Nelson and Tasman will face the most damage, followed by Southland, Northland, Otago and Gisborne.

The Manawatū-Whanganui and Taranaki regions are expected to face lower rates of damage, when accounting for population.

Flood damage is expected to become more common over time and a third of the damage could be attributed to future climate change, the report authors said.

In its most annual review, the Insurance Council estimated 675,000 New Zealanders — about one in eight — live in areas already prone to flooding.

Chief executive Kris Faafoi said long-term risks could be reduced “by prioritising and embedding resilience” and “making sure we don’t build in dumb places”.

University of Waikato environmental planning experts Silvia Serrao-Neumann and Christina Hanna have called for a national strategy, after recent Nelson-Tasman flooding.

The current “patchwork system”, they said, had resulted in inconsistent flood modelling, policy frameworks, public communication and regulations.

Emergency Management Minister Mark Mitchell told Newstalk ZB the Nelson-Tasman floods showed how persistent heavy rain could compound flooding effects.

“They’ve just had a rolling maul of weather. It meant that the ground couldn’t absorb water any more, which meant massive issues in terms of surface flooding,” he said.

Nelson Mayor Nick Smith told Newstalk ZB action was being taken to improve the city’s resilience, such as a new project along the Maitai River.

“We are strengthening stop banks, building flood walls and digging out portions of the river,” he said.

The Climate Sigma report was commissioned by the Environment Ministry to inform policy advice on the Government’s climate adaptation framework.

Michael Sergel is a senior reporter, usually based in Auckland. He has been covering business, politics, local government and consumer affairs for more than a decade.