Warming adds to storm’s rain: Study

Climate change added at least 10 per cent more rain to Hurricane Ian, a study prepared immediately after the storm shows.

Yesterday’s research, which is not peer-reviewed, compared peak rainfall rates during the real storm to about 20 computer models with Ian’s characteristics hitting Florida in a world with no human-caused climate change.

“The real storm was 10 per cent wetter than the storm that might have been,” said study co-author Michael Wehner, of the Lawrence Berkeley National Lab.

Forecasters predicted Ian will have dropped up to 61cm of rain in parts of Florida by its end.

Climate scientist Wehner and Kevin Reed, an atmospheric scientist at Stony Brook University, published a study in Nature Communications this year and found that during their rainiest three-hour periods hurricanes of 2020 were more than 10 per cent wetter than in a world without greenhouse gases trapping heat. Wehner and Reed applied the same attribution technique to Ian.

A rule of physics is that for every extra degree of warmth Celsius, the air in the atmosphere can hold 7 per cent more water.

This week the Gulf of Mexico was 0.8C warmer than normal, which should have meant about 5 per cent more rain. The flash study found the hurricane’s rainfall was double that. Ten per cent may not sound like a lot, but 10 per cent of 50cm is 5cm, which is a lot of rain, especially on top of the 50cm that already fell, Reed said.

Other studies have seen the same feedback mechanisms of stronger storms in warmer weather, said Princeton University scientist Gabriel Vecchi, who wasn’t part of the study.

MIT hurricane researcher Kerry Emanuel said in general, a warmer world does make storms rainier. But he said he is uncomfortable drawing conclusions about individual storms.

Vecchi said the world needs “to plan for wetter storms going forward”.