A new regional climate modelling project indicates that extreme rainfall from tropical cyclones affecting Aotearoa New Zealand could climb by as much as 35% by the end of the century if global emissions remain high.
The study, conducted by Earth Sciences New Zealand and the University of Waikato, examined projected cyclone behaviour across the southwest Pacific using high-resolution simulations based on multiple climate change scenarios.
The work builds on climate projections released last year in partnership with the Ministry for the Environment.
The researchers ran more than 1,800 years of simulated cyclone activity to explore how storm rainfall might change under different greenhouse gas pathways.
In every scenario, rainfall totals increased, with the steepest rise seen under the highest-emissions pathway.
While the overall frequency of cyclones was not projected to increase, the strongest systems – Category 4 or above – are expected to become more common.
The study also suggests wind speeds will intensify, although to a lesser degree than rainfall.
According to the research team, a warmer atmosphere’s ability to hold more moisture is a key factor.
More water vapour available to storms means greater potential for intense downpours.
New Zealand generally sees one or two ex-tropical cyclones each year, but high-impact storms remain relatively rare.
Recent history has shown their potential scale: Cyclone Gabrielle in February 2023 and the Auckland Anniversary weekend floods together caused an estimated $14.5 billion in damage, with insurers paying $3.8 billion in claims.
Previous cyclone assessments relied heavily on global climate models with coarse resolution – often around 100 kilometres per grid cell – making it harder to capture storm-scale details.
The new modelling narrows that to about 12 kilometres, offering a clearer view of the systems that could affect New Zealand.
The release of the modelling coincides with Willis’s latest Natural Catastrophe Review, which forecasts that insured losses in 2025 will again surpass $100 billion globally – continuing a seven-year run above that level.
This year’s loss tally has already been driven upward by the Los Angeles wildfires, now estimated at more than $40 billion in insured losses – alongside severe fires in Japan and South Korea, a record tornado season in the US, and Australia’s first cyclone landfall near Brisbane in half a century.
An above-average North Atlantic hurricane season is expected, heightening concerns for insurers and reinsurers about another costly year.
Against this backdrop, the Insurance Council of New Zealand | Te Kāhui Inihui o Aotearoa (ICNZ) is pressing for stronger national guidance on managing natural hazard risks.
It said the government’s draft National Policy Statement for Natural Hazards should give councils clearer authority to limit or prohibit development in high-risk zones.
ICNZ chief executive Kris Faafoi said intensifying hazards such as flooding, landslips, coastal inundation and sea-level rise demand a coordinated approach.
“New Zealand faces significant natural hazard risks, including flooding, landslips, coastal inundation and sea level rise and these risks are intensifying with the science indicating the prospect of more frequent and severe climate related events,” he said. “We support the government’s focus on strengthening the planning system to deal with natural hazards. A strong, clear national policy will empower councils to control development in areas exposed to high hazard risk.”
