The Upper Colorado River Basin lost nearly double the volume of groundwater compared to the Lower Basin during a severe drought between 2020 and 2022, upending long-held assumptions that the northern territory is naturally insulated from prolonged dry spells.
According to findings published in the journal Water Resources Research, the Upper Basin—encompassing Colorado, New Mexico, Utah, and Wyoming—depleted approximately 4.2 cubic miles (17.5 cubic kilometers) of groundwater over the two-year period. In contrast, the Lower Basin states of Nevada, Arizona, and California lost roughly 2.3 cubic miles (9.4 cubic km). Over the entire 2004 to 2023 observation window, total groundwater depletion across the basin reached 14 cubic miles (58.3 cubic km), with losses speeding up considerably after 2019.
Researchers analyzed surface water, soil moisture, snow-water storage, and satellite observations from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions to track aquifer shifts. The data showed that groundwater declines in the Upper Basin follow surface water drops with a short delay, meaning drought-depleted runoff and reduced Rocky Mountain snowfall directly compounded aquifer pumping. In the Lower Basin, however, groundwater drops sometimes preceded declines in surface water, indicating that steady, human-driven overuse is draining reserves irrespective of immediate surface water availability.
The Colorado River’s flow has dropped 35% compared to its 20th-century average, impacted by climate warming and century-old water allocation agreements made in 1922. The crisis pushed major storage reservoirs Lake Mead and Lake Powell to record lows in August. Lead author Esther Oyedele of Virginia Tech noted that regional planners must treat groundwater and surface rivers as connected systems rather than managing them independently, cautioning that subterranean aquifers cannot serve as an unlimited safeguard against ongoing warming and reduced snowpack.
Source: Live Science
