Upper Colorado River Basin groundwater loss exceeded Lower Basin's during drought

According to ScienceAlert, researchers from Virginia Tech and Indiana University Bloomington estimated that the Upper Basin lost roughly 4.6 trillion gallons of groundwater from October 2019 through September 2022. The Lower Basin lost around 2.5 trillion gallons over the same period.

The findings appeared in Water Resources Research. Lead author Esther Oyedele said the scale of Upper Basin losses was unexpected given its snowmelt-driven replenishment.

The Upper Basin's groundwater had been considered more resilient because mountain snowmelt replenishes it. The Lower Basin had been regarded as more vulnerable; those expectations provide context, not a measurement of earlier groundwater-loss rates.

The analysis also found a regional difference in how water shortages were connected. Surface-water deficits were strongly associated with the probability of groundwater drought in the Upper Basin, but the relationship was weaker in the Lower Basin. The article suggests that chronically limited surface water in the Lower Basin might make groundwater extraction less dependent on flows above ground; it does not establish that explanation as the cause.

Groundwater is a backup supply for people and agriculture when rivers and reservoirs run short. The reported findings put that reserve—not just visible surface water—at the center of the basin's water-management problem. Virginia Tech hydrologist Susanna Werth argues that protecting the basin requires managing water both above and below ground.