Top Highlights
- The “resilient” snowy Upper Basin took the biggest hit: During the 2020–22 drought, it lost nearly twice as much groundwater as the desert Lower Basin.
- The losses are massive: The Upper Basin lost about 4.6 trillion gallons,across the whole basin, groundwater has fallen by roughly 15 trillion gallons since 2004.
- Groundwater behaves differently across the basin: In the Upper Basin, losses followed surface-water shortages. In the Lower Basin, groundwater often declined first—possibly because of ongoing pumping.
- Managing rivers alone isn’t enough: Researchers say the basin needs better groundwater monitoring and coordinated management of both surface water and aquifers.
The mountain basin lost more than expected
When the Colorado River runs low, people often look to Lake Mead. Yet the 2020-22 drought exposed a less visible strain: groundwater fell fastest in the river’s snowy upper basin.
Researchers estimate that the upper basin lost 4.6 trillion gallons of groundwater during those three years, nearly twice the lower basin’s 2.5 trillion gallons. That upper-basin loss could fill about 7 million Olympic-size swimming pools. Snowmelt usually helps refill groundwater there, but it did not shield the region from drought.
What the satellites reveal — and what they do not
GRACE satellites track shifts in Earth’s gravity to estimate changes in water. Researchers used those readings, along with estimates of snow, soil moisture and reservoir levels, to calculate groundwater trends. The full basin lost about 15 trillion gallons of water from 2004 to 2023,groundwater accounted for roughly half.
The pattern differed by region. In the upper basin, groundwater shortages tended to follow surface-water shortages. In the lower basin, groundwater often began to fall first, possibly because people pump it regularly. Still, satellite readings cover broad areas, and the data show links, not causes. Sparse well records also limit checks in the upper basin.
Manage water above and below ground
The findings make a practical case for tracking rivers and aquifers together. More wells and finer satellite measurements could help communities spot declines sooner and plan withdrawals with clearer limits. Other river basins could adapt the same approach, though local monitoring would remain essential.
That work will not erase drought or settle every dispute over water. But better information can help farmers, cities and states make more durable choices. For a river that supports about 40 million people, learning to manage hidden water as carefully as visible water marks a useful step in our shared effort to live well in a changing climate.
Expand Your Tech Knowledge
Learn how the Internet of Things (IoT) is transforming everyday life.
Explore groundbreaking research and scientific advancements at the National Science Foundation (NSF).
ScienceV1
