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The climate crisis is causing heavier rainfall in the United States and increasing the threat of floods, according to a new study.

Researchers, from Northwestern University in Illinois, studied downpours in 17 different regions and found that the intensity of rainfall has increased over the past few decades.

“When people study how climate change has affected weather, they often look at extreme weather events like floods, heatwaves and droughts,” said Northwestern’s Daniel Horton, a study co-author.

“For this particular study, we wanted to look at the non-extreme events, which are, by definition, much more common. What we found is pretty simple: When it rains now, it rains more.”

The study, published on Tuesday in the journal Geophysical Research Letters, compared two distinct time periods, 1951-1980 and 1991-2020, with historical precipitation data.

The researchers then looked at the two time periods in 17 distinct climate regions in the US with different temperatures, precipitations, vegetation and ecosystem dynamics.

The researchers found that precipitation intensity (including rain and snow) had increased across much of the US particularly in the East, South and Midwest in recent decades. Changes in the US West were not detected.

“Not only do we see increasing precipitation intensity for regions east of the Rockies,” co-author Ryan Harp said, “but the intensities are becoming more variable as well, making water resource management even more challenging.”

Although this study does not attribute the changes in precipitation rates to climate change, Harp said the findings are consistent with human-caused global warming and climate model predictions.

University students in Florida use an inflatable mattress to evacuate an apartment complex near the campus that was totally flooded by rain from Hurricane Ian on September 30, 2022, in Orlando (AP Photo/John Raoux)

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“Warmer air holds more moisture,” he said. “For every one degree Celsius the atmosphere warms, it holds 7% more water vapor. So these observations are consistent with the predicted effects of human-caused global warming.”

More intense rainfall can lead to dangerous flash flooding and landslides and have severe impacts on infrastructure and agriculture.

The researchers say they hope the study’s findings can be used to better design infrastructure to counter the rising threat.

“You don’t need an extreme weather event to produce flooding,” Horton said. “Sometimes you just need an intense rainstorm.

“And, if every time it rains, it rains a little bit more, then the risk of flooding goes up.”

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