A team of Virginia Tech researchers has developed a satellite-based method that reveals how large dams alter river temperatures on a scale never before examined in the United States.
Using Landsat thermal infrared imagery, the scientists tracked surface water temperatures upstream and downstream of more than 250 of the nation’s largest dams from 2013 to 2024. They focused on rivers wider than 100 meters where the dams fully cross the channel. Temperature differences appeared in 71 percent of their observations. The size and direction of those shifts often depended on the type of dam and the season.
“Studying river temperatures up- and downstream of dams have been done before, but on 10 dams or less total,” said George Allen, associate professor of hydrology and remote sensing in the Department of Geosciences. “We’ve expanded this to over 250 dams, so we’re getting much more of a large-scale understanding what’s happening with river temperatures and dams.”
Previous work tended to focus on dramatic cases, such as China’s Three Gorges Dam. The new study captures subtler patterns across a broad sample of American rivers.
“A lot of the studies that are looking at single dams are looking at dramatic downstream impact. For example, something like the Three Gorges Dam in China is a very large dam that has very large effects,” said Emily Ellis, Ph.D. ’26, who received funding from a Future Investigators in NASA Earth and Space Science and Technology grant to support this project. “By grabbing a large portion of the dams in the U.S., we can see fine-scale differences, not just these large impacts.”
River temperature is a fundamental measure of water quality. Warmer water can fuel algal blooms that deplete oxygen and release toxins. Temperature swings also disrupt fish spawning and other natural cycles. Yet dams are usually operated for flood control, power generation, and water supply, with thermal effects treated as secondary.
“It’s important to know the impact that those dams are having, because in so many cases, dams are primarily managed for water movement and not temperature,” said Ellis, now a postdoctoral researcher at the University of North Carolina at Chapel Hill. “They’re thinking about preventing flooding, generating power — those kinds of things — and temperature is just a leftover piece.”
The automated satellite approach could extend beyond dams. Allen noted it might help track warming from power plants or data centers that discharge heat into rivers.
“This approach doesn’t just apply to dams,” said Allen. “We could be looking at other things, like power plants or data centers potentially warming rivers. I think we can use this automated technique and apply it to other systems as well.”
The findings appear in the journal Science Advances. By turning routinely collected satellite imagery into a practical tool for hydrology, the work gives water managers and ecologists a clearer picture of how human infrastructure reshapes the thermal life of rivers at continental scale.
