Rain today, reckoning ahead: Canterbury's flood bill set to be NZ's biggest

Thursday, 9 July 2026

Flooding will cause greater damage to road networks in future. Pictured is the Tyntesfield bridge, in Marlborough’s Waihopai Valley, destroyed this week by a flooded river.

Canterbury could face New Zealand’s biggest annual flood-damage bill for infrastructure by 2075, with power, water and road networks carrying most of the projected cost.

New modelling prepared for the New Zealand Infrastructure Commission estimates the region’s average annual infrastructure losses from inland and coastal flooding could rise from $65.1 million in 2025 to $113.6m by 2075 under a high-emissions climate scenario.

That would put Canterbury ahead of Waikato, at $107.1m, and Auckland, at $97.1m.

Dave Broadhurst was one of hundreds in Kaikoura impacted by flooding this week.

The figures do not mean Canterbury should expect one $113.6m flood every year. They are an annual average across many possible events, including years with little damage and years when the repair bill would be far higher.

The report comes as intense rain drenched the South Island's east coast this week, with inland areas near Kaikōura recording up to 340mm in just 60 hours. Kaikōura itself received 162.4mm — nearly triple its average July rainfall in just three days.

The deluge caused rivers to overflow, washed away bridges and damaged roads. Surface flooding, gravel movement and significant damage to local infrastructure was reported across Kaikōura, Selwyn and Hurunui districts.

The research, carried out by Earth Sciences New Zealand, says flood-related infrastructure losses are expected to rise across the country over the next 50 years, but not evenly.

It says flood-related financial losses are expected to exceed those from any other natural hazard in most regions over the coming decades.

For the South Island, the biggest dollar figure sits with Canterbury, but territorial authorities such as Waimakariri, Buller, Invercargill, Nelson and Tasman face sharper exposure where flood losses are high compared with the size of local infrastructure networks.

The commission said the work was designed to help governments and infrastructure owners decide where flood-protection spending would make the most difference.

“Infrastructure decisions made today will shape New Zealand for decades,” said Graham Campbell, the commission’s director of economics and research.

“If we don’t size the risk, investment decisions risk being either too cautious or too costly,” he said.

On the West Coast, average annual infrastructure flood losses are projected to almost double, from $12.2m in 2025 to $23.8m by 2075 under the same high-emissions scenario.

Westport has suffered multiple floods, impacting streets and private homes. This picture was taken in 2021.

Nelson-Tasman’s losses rise from $13.3m to $25.3m, while Southland’s increase from $19.4m to $28.1m.

For the West Coast and Nelson-Tasman, the private-building figures add another layer.

Both areas are among those where flood losses to homes and businesses are high relative to asset values, meaning the pressure may not fall only on public infrastructure budgets, but also on households, insurers and business owners.

“Annual flood damage to private buildings is forecast to grow significantly over the next 50 years,” said Dr Nick Horspool, senior natural hazard risk scientist at Earth Sciences New Zealand.

Severe damage to the Cribb Creek Bridge meant the Inland Kaikōura Rd was closed.

Waimakariri stands out as one of the South Island districts where flood losses are high compared with the size of its infrastructure network.

The modelling estimates the district’s average annual infrastructure flood losses could rise from $13.6 million in 2025 to $25.5m by 2075 under the high-emissions scenario.

As a share of infrastructure value, that is projected to climb from 0.53% to 0.99% a year. That puts Waimakariri among the most exposed territorial authorities in the country.

The largest projected costs in 2075 are in electricity, at $9.2m, water networks, at $8.5m, and local roads, at $5.2m.

The district’s private-building losses are also projected to rise, from $7.8m in 2025 to $13m by 2075.

The estimates are not the full economic cost of future floods. They count direct damage to infrastructure assets, but not the wider disruption when roads close, freight is delayed, customers cannot reach businesses, or workers cannot get to their jobs.

The modelling also excludes some major infrastructure sectors, including ports and airports, and does not include rainfall-triggered landslides.

Additional reporting by Elsie Williams