Future floods: Global warming intensifies heavy rain -- even more than expected

The intensity and frequency of extreme rainfall increases exponentially with global warming, a new study finds. The analysis by researchers from the Potsdam Institute of Climate Impact Research (PIK) shows that state-of-the-art climate models significantly underestimate how much extreme rainfall increases under global warming -- meaning that extreme rainfall could increase quicker than climate models suggest.

"Our study confirms that the intensity and frequency of heavy rainfall extremes are increasing exponentially with every increment of global warming," explains Max Kotz, lead-author of the study published in the Journal of Climate. These changes follow the physical theory of the classic Clausius-Clapeyron relation of 1834, which established that warmer air can hold more water vapour.

"State-of-the-art climate models vary on how strongly extreme rainfall scales with global warming and that they underestimate it compared to historical observations."

"Climate impacts on society have been calculated using climate models. Now our findings suggest that these impacts could be much worse than we thought. Extreme rainfall will be heavier and more frequent. Society needs to be prepared for this," says PIK department head and author of the study Anders Levermann.

Changes in the frequency and intensity of daily rainfall extremes over land can impact social welfare, the economy and social stability, given their link to flooding but also ground-water availability, which can cause considerable loss of life and financial losses.

Stronger increases of extremes across tropical regions

The researchers at PIK analysed the intensity and frequency of daily precipitation extremes over land in 21 state-of-the-art climate simulations (CMIP-6) and compared the changes projected by CMIP-6 models to those observed historically.

The method they applied draws on pattern-filtering techniques, allowing them to separate which changes in the climate system are forced by human emissions, and which are not.

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