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Flood risk on the rise: Climate change models point to more persistent heavy rainfall

Extreme weather events are becoming more frequent as a result of climate change. River floods such as those along the Ahr and Meuse valleys in 2021, the Central European floods of last September and the recent floods in Valencia, Spain, are caused by so-called cut-off lows. The Wegener Center at the University of Graz has now for the first time investigated how these storms could change with climate change.

"We expect that persistent cut-off lows north of 40 degrees latitude and in East Asia will occur earlier in the year. Canada, northern Europe, Siberia and China in particular will have to prepare for more heavy and prolonged heavy rainfall in spring," says project leader Douglas Maraun. The results of the study have just been in the journal Communications Earth & Environment.

A cut-off low is a low-pressure system located at an altitude of several kilometers that is cut off the polar front. Since it often stays in the same place for several days, it can lead to long periods of heavy precipitation in this region.

Despite their devastating consequences, there has been little research to date into how such storms could change in a warming climate. In cooperation with colleagues from the University of Reading, United Kingdom, and the Institute of Atmospheric and Climate Sciences in Bologna, Italy, scientists from the Wegener Center at the University of Graz have now conducted the first detailed study addressing this question.

Aditya Mishra, first author of the study, explains, "We analyzed 18 different climate models with regard to such storms. To do this we essentially read out weather maps from the models every six hours and used them to analyze the paths and intensity of such storms."

By comparing all 18 models, the scientists were able to estimate robust changes very well. "In general, these storms will occur more northward and their season expands from summer and autumn further into spring," Mishra summarizes. He is now a postdoc at the University of Uppsala in Sweden after completing his Ph.D. at the University of Graz.

Whether a heavy precipitation event turns into a disaster also depends on flood protection. "With targeted measures such as renaturation and a functioning early warning system, we can at least partially protect ourselves from extreme weather and the impacts of climate change," emphasizes Douglas Maraun.