Groundwater levels in the Colorado River Basin are declining rapidly, with recent losses in the Upper Basin significantly exceeding those in the Lower Basin. A study by Virginia Tech researchers, published Tuesday in the journal Water Resources Research, found that these underground water reserves are shrinking as the region faces ongoing drought and human demand.
The research analyzed NASA satellite data alongside estimates of soil moisture, surface water, and snow storage from 2004 to 2023. Historically, the Upper Basin—which includes Colorado, New Mexico, Utah, and Wyoming—has been more resilient than the Lower Basin due to snowmelt from the Rocky Mountains. However, the study found that between 2020 and 2022, this trend reversed during a period of severe drought.
During that window, the Upper Basin lost approximately 4.6 trillion gallons of groundwater, while the Lower Basin—encompassing California, Arizona, and Nevada—lost about 2.5 trillion gallons. Author Esther Oyedele noted that groundwater serves as a vital alternative source when surface reservoirs like Lake Mead and Lake Powell reach record lows. The researchers stated that the Upper Basin has reached a turning point characterized by rapid storage loss.
A person living in Arizona, California, or Nevada may notice the effects of this scarcity through mandatory water cuts, which were established in a new operating plan published in August. As surface water allocations are reduced, reliance on groundwater typically increases; however, the study indicates that groundwater should not be viewed as an unlimited reserve. The decline in the Upper Basin is particularly notable because snowmelt, which normally recharges these aquifers, has been reduced by higher temperatures and prolonged drought.
The knock-on effects extend to the broader management of the river, as groundwater and surface water are linked through springs and soil seepage. If groundwater levels continue to fall, it may reduce the amount of water that naturally feeds into the Colorado River, further straining reservoirs. The study did not quantify the exact remaining volume of groundwater or the specific percentage of loss caused by climate change versus human extraction. Moving forward, the basin states are operating under a new management plan as of August, and researchers suggest that future policy must account for these losses to ensure long-term regional water security.