The new report, 'When Waters Rise: Climate Change, Regional Risk and Infrastructure Investment', says flood-related financial losses in some regions will increase under different climate scenarios, with the financial losses caused by flood damage to exceed that of other natural events.

It says New Zealand could face up to $165m worth of losses from coastal flooding and another $300m from inland flooding in the next 50 years.

The report gives scenarios for specific types of infrastructure, including road and rail networks, government buildings, telecommunications and electricity.

Separately, it assesses the "likely impacts" on private infrastructure including housing.

It says the West Coast is expected to incur the highest losses to private buildings in proportion to asset value, followed by Hawke's Bay and the Bay of Plenty.

But West Coast councillor Allan Birchfield, the former chairman, says the report overlooks that West Coast infrastructure -- including the three main towns of Hokitika, Greymouth and Westport -- were historically built on flood plains and flooding was nothing new.

"Much of our development and infrastructure is built on flood plains. These areas were created by river deposits over thousands of years, and occasionally the rivers will return.

"There is nothing new or accelerated in the flood events. It's just that we have built in the way," Cr Birchfield said today.

The main cause for some of the more recent flooding was his own council not always taking responsibility -- a factor he said was at play in the Westport floods.

"One of the main contributors to the flood damage is the failure of our regional councils to maintain our drainage channels and waterways. Anyone else attempting to clear these channels is shut down or prosecuted, as has happened on the West Coast many times."

Westport is in the midst of a substantial flood system upgrade led by the West Coast Regional Council after the town was badly affected by floods in July 2021 and in February 2022. The town has survived multiple floods in its 160-year history, including a record flood in 1926.

A submission made by Te Uru Kahika Regional and Unitary Councils of Aotearoa in 2023 said had the Government spent $10m on flood adaptation assistance, the $100m spent on mopping up the damages caused by the flood could have been avoided.

The 2021 Westport floods sparked insurance claims of over $73m for homes, contents and lost vehicles.

The Government responded with $17.08m for a temporary village for affected residents in the wake of the event. A co-funded flood protection scheme worth $25.8m is now under way, including a 16km-long ring stopbank system plus new flood warning systems, emergency planning, and a 50-year adaptation plan.

Invited to comment today, council chief executive Darryl Lew did not engage with Cr Birchfield's claims but was committed to complete the work started.

"In addition, we are working to increase our standard flood protection warning across the region. This includes extending the flood forecasting we do in the Buller to other catchments," Mr Lew said.

LDR is local body journalism co-funded by RNZ and NZ On Air.