Upper Colorado Basin Groundwater Loss Outpaces Lower Basin Amid Drought A new analysis of groundwater reserves in the Colorado River Basin reveals that the Upper Basin - comprising Colorado, New Mexico, Utah, and Wyoming - suffered nearly twice the groundwater loss as the Lower Basin during the 2020-2022 drought. This finding challenges the long-held assumption of the Upper Basin's greater resilience and highlights the severe impact of reduced snowpack and increased evaporation on regional water security. Western states that were thought to be resistant to prolonged drought may be more vulnerable than scientists previously believed, a new analysis of groundwater reserves in the Colorado River Basin finds. Researchers revealed the four states that together make up the Upper Basin - Colorado, New Mexico, Utah and Wyoming - lost almost twice as much groundwater as the Lower Basin did during an intense drought between 2020 and 2022. The finding was unexpected and might signal a turning point for the region, because the Upper Basin has long been seen as more resilient to dry spells than the Lower Basin, said the study's lead author, Oyedele.