Carbon emissions exacerbating the Western US water crisis

In the western US, limited water supply and high demand--accentuated by anthropogenic climate change--have resulted in overallocated water resources and rapidly depleting groundwater. Simultaneously, legal and policy mechanisms are being pursued regarding the contributions of large emitting entities (“Carbon Majors”) to such impacts. Here, we quantify impacts on western US water resources attributable to the Carbon Majors, and compare results with a simpler-to-use (‘proportional’) approach. Anthropogenic climate change has driven large decreases in water supply (snowpack and streamflow) and increases in water demand (irrigation demand), with roughly half attributable to the Carbon Majors. These changes have led to a widening seasonal gap between water supply and demand, and with Carbon Majors emissions accounting for ~1/3 of observed, climatically-driven groundwater loss in the Central Valley during 2003-2024. Though both approaches yield similar results, consistent over- and underestimations are present in each variable, suggesting caution is needed when using the proportional approach.