This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Declining Colorado River flows and falling water levels at Lake Powell and Lake Mead are highly visible signs of the Southwestern megadrought. Unseen below ground, groundwater reserves in the Colorado River Basin are disappearing just as fast—and in an unexpected new pattern, according to research from Virginia Tech.
Historically, groundwater has declined more in the Lower Basin. But the system has hit a turning point: The Upper Basin is now experiencing rapid groundwater losses, with surface-water shortages increasingly affecting groundwater as well. To isolate changes in groundwater stocks across both basins, Virginia Tech's Susanna Werth and a team of geoscientists combined measurements from NASA's Gravity Recovery and Climate Experiment satellite mission with estimates of surface water, soil moisture and snow-water storage from 2004 to 2023.
Their findings were published in Water Resources Research. Results point to an acceleration in groundwater depletion after 2019. During the severe drought from 2020 to 2022, the Upper Basin lost about 4.6 trillion gallons (17.4 trillion liters) of groundwater.
This was nearly double the loss in the Lower Basin, which was estimated at 2.5 trillion gallons (9.5 trillion liters). "We generally think of the Upper Basin as more resilient because of its snowmelt-driven recharge," said lead author Esther Oyedele, a geosciences graduate student at Virginia Tech. "I did not expect to see so much groundwater loss there during the recent drought.
What surprised me even more was that groundwater did not track surface-water shortages in the same way in the Upper and Lower Basins." The Colorado River Basin provides water for roughly 40 million people and extensive agricultural operations. As rivers and lakes dry up, groundwater can become a critical buffer against shortages—but that buffer is not unlimited. "Continued groundwater depletion, especially in the Upper Basin, could further reduce groundwater contributions to rivers and intensify the feedback between groundwater loss and surface-water shortages," said Werth, an assistant professor of hydrology and remote sensing.
The study sends a clear signal, Werth said. "Looking at surface water alone is no longer enough. Protecting the Colorado River Basin requires managing the water above and below ground." E.
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