Study finds groundwater losses in the Colorado River Basin are accelerating in surprising ways

A new Virginia Tech study is drawing attention to a second, less visible water crisis in the Colorado River Basin: groundwater is declining rapidly beneath the drought-stricken Southwest, and the loss is happening in unexpected ways. The research found that basin-wide groundwater has been shrinking for two decades, with losses speeding up after 2019 and becoming especially pronounced during the 2020-2022 drought.

The findings matter because groundwater has long served as a buffer when surface-water deliveries from the Colorado River fall short. As Arizona, California and Nevada face deeper cuts under the basin’s new operating rules, shrinking aquifers could leave communities, farms and water managers with fewer fallback options.

The study, published in Water Resources Research on Oct. 13, 2026, used NASA GRACE and GRACE-FO satellite observations along with hydrologic data sets to estimate storage changes across the basin from water year 2004 through 2023. The researchers reported a major shift in the drought era: during 2020-2022, the Upper Basin lost groundwater faster than the Lower Basin, reversing the historical pattern seen in earlier work.

An overlooked source of water stress

The Colorado River Basin stretches across parts of seven western states and is a critical water source for tens of millions of people. The new research adds to a growing body of evidence that the basin’s water crisis is not confined to reservoirs such as Lake Mead and Lake Powell; underground supplies are also being depleted. Earlier studies had already shown long-term groundwater losses in the basin, but the latest analysis suggests the distribution of those losses is changing in ways scientists did not expect.

Researchers said the pattern underscores the need to look at the river system and the aquifers connected to it as one water ledger rather than separate problems. The shift is especially significant for Arizona, where groundwater has historically been used to help offset shortages in Colorado River deliveries. With reservoir levels still under pressure and new federal cutbacks approaching, the basin’s hidden water supply is becoming harder to ignore.

The study does not resolve how quickly individual local aquifers may recover, but it does suggest that the basin’s long-running drought is reshaping both visible and invisible water stores at the same time. For water planners across the Southwest, that could make future shortages more complex than reservoir levels alone indicate.