Cyclone Gabrielle's impact was felt all around Northland. Photo: Kaipara District Council / Supplied
A top climate scientist says damaging storms such as Cyclone Gabrielle may not become more frequent as a result of climate change - but they will become more intense.
The warning comes as the Far North District Council considers opting in to a scheme which would see the council and central government split the cost of buying out properties damaged in Cyclone Hale, the Anniversary Weekend storm or Cyclone Gabrielle in early 2023.
To be eligible for the buy-out, any properties must also pose an intolerable risk to human life in future floods.
Councillors backing the scheme said it is a one-off chance to help people move off land where their lives are in danger.
Others worry about the precedent of asking ratepayers to bail out homeowners affected by one particular storm, when floods are expected to worsen as a result of climate change.
Sam Dean, NIWA's principal climate scientist, said cyclones would likely become more severe, but not necessarily more frequent.
He said Northland was particularly affected by ex-tropical cyclones, with an average of one passing within 500km of the region each year.
Top Energy workers remove a fallen tree from powerlines after Cyclone Gabrielle. Photo: Top Energy
"We don't expect ex-tropical cyclones to get more frequent, although when they do happen they will carry more moisture and tend to be more severe. That increases the amount of rain and flooding that those ex-tropical cyclones cause."
Dean said not every cyclone left a lot of damage.
The worst ones, like Gabrielle in 2023 and Bola in 1988, were those that moved slowly across the country.
"A lot of them move through the northern region quite rapidly, and so they don't have time to do a lot of damage. They might just flick through. But if a tropical cyclone stalls, like Gabrielle, and becomes quite slow moving, then it can be really damaging," he said.
"It wasn't like a world-record-shattering record cyclone. It was more that it became slow-moving and that allowed it to sit there continuing to do damage in particular parts of the country for a sustained period of time. A lot of our worst storms are like that. It's not just how bad is the storm, but also whether it flies on by or gets stuck and re-intensifies."
A sign at the Brynderwyns in March this year, a month after Cyclone Gabrielle hit. Photo: Local Democracy Reporting/ Northern Advocate - Michael Cunningham
Dean said there had been three or four extremely damaging cyclones in Northland in the past century or so.
"That probably gives you a good indication of how often they happen. But climate change is a massive kind of crazy experiment with the planet where we're changing the fundamentals of how the climate system works, and the outcome of that is going to give a few surprises along the way.
"I don't think it's possible to predict with certainty how this is going to go, so people need to be aware of the chance of surprises and things that 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.
The number of homes that could be affected is expected to be about 21, but it could end up as low as two.
Councillors will decide in November whether to push ahead with the buyouts.
The FOSAL scheme applies only to general land.
A separate, fully government-funded scheme applies to whenua Māori, Māori land.
Up to 18 homes and marae across the Far North could be eligible under that scheme.