Rainfall is becoming more intense in the United States

A new study from Northwestern University suggests that rainfall intensity is increasing across much of the United States. The research team analyzed 17 different climate regions and compared their rainfall during two distinct periods: 1951-1980 and 1991-2020.

“When people study how climate change has affected weather, they often look at extreme weather events like floods, heatwaves and droughts,” said study senior author Daniel Horton. “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 researchers found snow and rain intensity increased in the East, South, and Midwest. However, the Western states have not experienced an increase in precipitation. 

“Not only do we see increasing precipitation intensity for regions east of the Rockies, but the intensities are becoming more variable as well, making water resource management even more challenging,” said study first author Ryan Harp, a researcher in the Institute for Sustainability and Energy at Northwestern.

While this study does not confirm that climate change causes more intense precipitation, the results are consistent with climate change. 

“Warmer air holds more moisture,” Harp explained. “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 precipitation can lead to increased incidents of flooding and landslides, which threaten lives and livelihoods. The researchers hope their findings will encourage policymakers and city managers to build infrastructure to withstand the changes. 

“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.”

The study is published in the journal Geophysical Research Letters.

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By Erin Moody , Earth.com Staff Writer