Extreme rainfall from Hurricane Ian worsened by climate breakdown – study
US researchers find human-induced global heating has increased intensity of downpours in powerful mega-storm
Oliver Milman, @olliemilman, Fri 30 Sep 2022 12.04 EDT
Human-induced climate change increased the extreme rainfall brought by Hurricane Ian, which has devastated parts of Florida, by more than 10%, according to a new preliminary analysis.
Ian has caused widespread damage and at least 21 deaths since crunching into south-west Florida on Wednesday, tearing asunder cities such as Fort Myers and Cape Coral with winds that reached close to 150mph and a storm surge that in places reached 18ft. More than 2 million people have been left without power as the storm has rampaged across the state and moved northwards to the Carolinas.
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Much of the damage has been due to torrential rainfall, with the new analysis finding that the heating of the atmosphere and ocean due to human activity has added significantly to the intensity of these downpours.
The study, which is preliminary and yet to be peer reviewed, found that the amount of rain dumped by the storm was 10% higher because of the climate crisis. Scientists used a methodology established in previous research that rainfall during the 2020 Atlantic hurricane season was up to 11% heavier due to global heating.
“That sort of increase in rainfall isn’t small when it’s on top of an already intense storm,” said Kevin Reed, a researcher at Stony Brook University who undertook the new work. “It can really have significant effects, as we’ve seen with the extensive rainfall across Florida. It has had a widespread effect.
“If you’ve got 1ft in rainfall over a day, 10% more adds an inch or so more, which is a lot in itself. It can really amplify the impacts.”
The heating of the atmosphere, through the burning of fossil fuels, has caused it to accumulate more water in many places – about 7% more water for every extra 1C (1.8F) it warms. This can then be unleashed in heavy precipitation events that can quickly inundate houses and businesses.
“These are conservative estimates on the human-induced increases in rain using our peer-reviewed method,” said Michael Wehner, a climate scientist at the Lawrence Berkeley National Laboratory who worked on the new analysis with Reed. “Climate change didn’t cause the storm but it did cause it to be wetter.”
Hurricanes derive much of their strength from heat in the ocean, and the Gulf of Mexico’s water temperature is about 0.8C (1.4F) above the long-term normal, leading scientists to point to a trend of storms rapidly gathering pace, in part due to global heating.
In the case of Ian, what was a tropical storm morphed into a hurricane in less than 24 hours, ballooning further into something that was near to a category 5 storm, the fiercest category of storm, which has winds powerful enough to rip roofs off buildings. This sort of rapid intensification has happened several times in recent years alone the US Gulf coast, such as Hurricane Ida, which caused widespread chaos in Louisiana last year.
“We are seeing much clearer indicators in these events, for sure,” Reed said. “It’s a good reminder that while we’ve had a relatively quiet hurricane season until this storm, we still have two months of the season left and we need to be really prepared.
“The reality is that climate change is here, and it’s altering events here and around the world. It’s important that we realize this when we think about disasters like this.”