Rising sea levels could leave some New Zealand coastal properties without access to insurance as the risk of damage increases, a research report warns.

“Insurance covers risks for which there is significant uncertainty,” the Motu Economic and Public Policy Research report says. “As such, insurers will retreat from coastal locations once risks are sufficiently probable.”

Wellington-based Motu is regarded as New Zealand’s leading independent research institute. Its research says king tides and storm surges are expected to become more frequent, while waves will reach further inland with rising global sea levels.

A 10cm ocean rise could see the one-in-100-year storm surge risk in Wellington become a one-in-20-year threat, the report says. A 30cm rise could make storm surges an annual danger in Christchurch and Wellington.

New Zealand sea levels are projected to rise 30cm by 2065, according to the Parliamentary Commissioner for the Environment.

“Climate change will inevitably threaten New Zealand’s coastal housing, but the exact nature of that threat will depend on the insurance options available,” Motu says.

One such option could “involve a pre-agreed schedule of premiums, which would increase over time and could be contingent on observed sea level rise”.

The increasing schedule could convey to buyers the likely costs of coastal home ownership and help banks avoid mortgaging properties that would later become uninsurable.

The report calls for research on the risk split between homeowners, government and insurers, policy options for when a “tipping point of uninsurability” is reached, and options for mitigation and better information for coastal property owners.

There are 43,683 homes in New Zealand within 1.5 metres of the present average spring high tide, and 8806 homes within 50cm, based on regions with high-quality data.