More Intense Rainfall Happening Across the U.S., Study Finds

A new study from Northwestern University has found that it is raining more intensely in most regions of the U.S. In places that once received lighter rainfall, more recent decades have brought moderate to heavy rainfall, especially in the central and eastern parts of the country.

Researchers studied rainfall in 17 regions around the U.S. and found heavier rainfall patterns in most of the regions they observed. They published their findings in the journal Geophysical Research Letters this month.

The study compared precipitation intensity from 1991 to 2020 to precipitation in the years 1951 to 1980. The researchers compared observations of rainfall in more recent decades to historical precipitation data from the National Oceanic and Atmospheric Administration (NOAA)’s Global Historical Climatology Network database.

Many regions, especially those east of the Rocky Mountains, are seeing harder rainfall each year. Precipitation east of the Rocky Mountains has seen about a 5% increase, although the researchers did not observe major intensity changes in rainfall on the Pacific Coast or over the Rocky Mountains.

“When people study how climate change has affected weather, they often look at extreme weather events like floods, heatwaves and droughts,” Daniel Horton, senior author of the study and assistant professor of Earth and planetary sciences at Northwestern University, said in a statement. “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 eastern, southern and midwestern parts of the U.S. saw the most changes in intensity, while precipitation has remained largely the same around the western U.S., according to the study. 

Study author Ryan Harp, an Ubben Postdoctoral Research Fellow at the Institute for Sustainability and Energy at Northwestern, explained that the precipitation intensity is increasing and becoming more variable, which can lead to challenges with water resource management. As such, Harp and Horton plan to further research the variability of annual precipitation and the frequency of precipitation across the U.S. 

While there are studies on climate change and extreme weather events, the researchers note that day-to-day rainfall changes can also put communities at risk. More information on this topic could help communities plan for more resilient infrastructure that can withstand changing precipitation patterns, which match up with existing climate prediction models that factor in the effects of global warming. 

“You don’t need an extreme weather event to produce flooding,” Horton explained. “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.”