Study Charts Drought Impacts on CRB Groundwater
A study of drought impacts on water storage in the Colorado River Basin, published in the October issue of Water Resources Research, documents sustained groundwater depletion over the past two decades. The authors, from Virginia Tech and Indiana University, point to an acceleration of storage losses after 2019, particularly with the 2020–2022 drought. This period was characterized not only by reduced precipitation but also by higher temperatures, which exacerbate drought impacts on snowmelt, runoff, evapotranspiration, and soil moisture. Human water consumption, which tends to increase during hot droughts, is a compounding factor in storage loss.
Within the Colorado River Basin, limited natural groundwater recharge in the Lower Basin dampens climate impacts and renders groundwater storage vulnerable to depletion. A focused look at Arizona’s Active Management Areas confirmed that decreases in groundwater storage were attributable to increased consumption due to drought and Colorado River shortage reductions rather than surface water–groundwater interactions. In contrast, in the Upper Basin, with its greater precipitation and generally strong groundwater–surface water interactions, groundwater storage rebounds between droughts. Increasing drought frequency and duration, however, coupled with human consumption, are producing long-term groundwater storage declines there as well.
The study used GRACE satellite-based observations supplemented with in situ groundwater well data. GRACE has revealed eye-opening, world-wide groundwater depletions. The authors concur with previous studies in concluding that the disappearance of groundwater in the Colorado River Basin, which exceeds the loss from the system’s major surface reservoirs, requires management approaches capable of reversing long-term depletion of critical groundwater reserves in the region.