Researchers Unlock New Tool To Study River Temperatures Over Large Scales

Satellite imagery captures the impact of large U.S. dams on river temperatures over the last decade.

A team of Virginia Tech geoscientists found a new way to look at the widespread impacts of dams on river temperatures: using Landsat thermal infrared imagery to gather data on rivers across the United States.

By using satellite imagery instead of site-specific on-the-ground measurements, researchers can draw from a much larger pool of data.

“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.”

The study, recently published in Science Advances, tracked water temperatures up and downstream for more than 250 of the largest dams in the United States from 2013-24.

Measuring thermal impact

Due to limitations of satellite image resolution, the research team targeted dams located in the United States on rivers greater than 100 meters in width. In addition, the dams had to cross the entire river, creating a large obstruction. Thermal imaging was then used to create river surface temperature profiles extending both up- and downstream.

The research findings echoed what has already been demonstrated in previous studies: that dams do alter downstream temperature. In fact, temperature differences were found in 71 percent of the study’s observations.

However, the data also showed that differences could vary based on dam type or the season. Temperature variances may also be on a smaller scale than what previous studies have shown.

“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.”

Why temperature matters

Temperature, one of the core parameters of water quality, is fundamental to the ecosystem health and biochemistry of a river. For example, water that is too warm can encourage the growth of algal blooms, which deplete oxygen and produce toxins. Thermal fluctuations can throw off the timing of natural processes like fish spawning, which is driven by temperature cues.

“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.”

Why scope matters

Allen said that in the field of hydrology, research has been progressing to a global scale to determine how water systems react to climate change and land use change. But many of these studies have focused on warming temperatures in lakes. There haven’t been many studies focusing on river temperatures on a large scale.

By introducing satellite imagery as a tool to study rivers on a broader scale, scientists can take away a better understanding of the effects of dams and its implications for freshwater ecology and water resource management.

While this particular study focused on the impacts of dams, the use of satellite imagery could be used to investigate the effects of other manmade structures on river temperatures.

“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.”