As the frequency and intensity of heatwaves increase across the U.S., a similar but more striking phenomenon is occurring in American rivers. Analysis of data from nearly 1,500 sites in the contiguous United States between 1980 and 2022 revealed that heatwaves in rivers are accelerating faster than and lasting nearly twice as long air heatwaves, according to a new study by researchers at Penn State.
"Rivers are often thought of as safe and cool havens protected from extreme temperatures," said Li Li, corresponding author and Barry and Shirley Isett Professor of Environmental Engineering in Penn State's Department of Civil and Environmental Engineering. "Our study shows, for the first time, that rivers are experiencing a more rapid increase in frequency, duration and intensity of heatwaves than air, and are increasing at about two to four times the rate of air heatwaves."
The research, published in the journal PNAS, found that periods of abnormally high riverine water temperatures are a threat to aquatic ecosystems, water quality and America's food supply and energy stability.
"Our findings show that riverine heatwaves are increasing faster than air heatwaves, a trend likely happening worldwide," said Kayalvizhi Sadayappan, lead author and postdoctoral scholar in the Department of Civil and Environmental Engineering at Penn State. "This raises the risk of rivers experiencing both extreme heat and low water flows at the same time, which can cause conditions that can lower oxygen levels, stress aquatic life and even trigger large-scale fish die-offs."
