A climate scientist’s prediction for future ex-tropical cyclones: More moisture, stronger

Others worry about the precedent of requiring taxpayers to help homeowners affected by a particular storm when flooding is expected to worsen due to climate change.

Sam Dean, Niwa’s chief climate scientist, said hurricanes would likely become more severe, but not necessarily more frequent.

He said Northland was particularly affected by former tropical cyclones, with an average of one passing within 500km of the region each year.

“We do not expect ex-tropical cyclones to become more frequent, although when they do occur they carry more moisture and tend to be more severe. This increases the amount of rain and flooding that these former tropical cyclones cause.”

Dean said not every cyclone caused extensive damage.

The worst, like Gabrielle in 2023 and Bola in 1988, slowly spread across the country.

“Many of them move through the northern region quite quickly and therefore do not have time to cause much damage. Maybe they just browse through. But when a tropical cyclone like Gabrielle stalls and moves very slowly, that can be really damaging,” he said.

“It wasn’t a world record-destroying record cyclone. Rather, it slowed down, allowing it to continue to cause damage in certain parts of the country over a longer period of time. Many of our worst storms are like this. It’s not just a matter of how bad the storm is, but also whether it passes or gets stuck and intensifies again.”

Dean said there have been about three or four extremely damaging cyclones in Northland in the last century.

“That probably gives you a good indication of how often they happen. But climate change is a huge, crazy experiment on the planet in which we are changing the fundamentals of how the climate system works, and the outcome will throw up some surprises along the way.

“I don’t think you can predict with any certainty how this will play out, so people need to be aware of the possibility of surprises and things they’ve never experienced before.”

Far North District Council staff are currently carrying out assessments of homes that could be eligible for the Government’s Future of Severely Affected Land (Fosal) voluntary buyout scheme.

It is expected that around 21 houses could be affected, but in the end it could only be two.

City councilors will decide next month whether to move forward with the takeovers.

The Fosal scheme only applies to general properties.

A separate, fully government-funded program applies to whenua Māori, Māori land.

Up to 18 homes and marae in the Far North could be eligible under this scheme.

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