Cyclone Gabrielle the 'new benchmark' for future storms in New Zealand - researcher

• A NIWA study shows climate change led to 10 percent more rain during Cyclone Gabrielle than would have in pre-global warming conditions.
• Nearly a quarter of the rain expected in a year fell on northeastern parts of the country in February 2023.
• The storm claimed 11 lives and caused nearly $13.5b worth of damage.
• Researchers say further increases in global temperatures will lead to more extreme storm events.

NIWA climate scientists say a recent study shows climate change increased the amount of rain that fell during Cyclone Gabrielle by 10 percent.

Almost a quarter of the rain expected in a year fell over the northeast of Aotearoa during the storm in February 2023, claiming 11 lives and causing an estimated $13.5 billion in damage.

NIWA's Dr Dáithí Stone said researchers collaborating with MetService, Bodeker Scientific, the University of Waikato and the Norwegian Meteorological Institute compared the MetService forecasts for the storm against conditions that preceded the current 1.1C rise in average global temperatures.

"Cyclone Gabrielle resembled some of the worst-case scenarios that we could have predicted for the region," Stone said.

"We therefore wanted to see how much climate change influenced its power, so we compared the actual MetService forecast of the storm against forecasts under conditions representative of a climate without human interference. Our study found a significant increase in rainfall under human-influenced conditions."

She said the atmosphere - warmed by human activity following the Industrial Revolution - held more water, which fuelled storm systems and increased wind speeds.

"Our findings resemble results from similar experiments looking at tropical cyclones elsewhere in the world, so it's not something specific to New Zealand."

Stone said the researchers applied the forecasts to conditions where global temperatures had been allowed to climb further and found even more rain would be a likely consequence.

"The best way to tackle future storms is to reduce our greenhouse gas emissions to halt, or even reverse, the warming of our climate. But until then, Cyclone Gabrielle must form our new benchmark for preparing for any future natural disaster."

MetService chief meteorologist Chris Noble said the research was vital to help understand the impact of climate change on storms in Aotearoa.

"We know the world is warming and the approach we've used gives unique insights into how quickly the severity of storms is increasing.

"Studies like this help the public understand climate change impacts here in New Zealand and may help inform policy and adaptation strategies in the future."