Carbon Emissions Exacerbate the Western US Water Crisis

Water has long been a limiting resource in the world’s arid regions. In the western United States, an arid climate and demand from the region’s multibillion dollar agricultural industry have led to water shortages, legal disputes regarding water rights, and excessive overdraft of groundwater.  Climate change is compounding these challenges by simultaneously reducing supply and increasing demand. Here, we combine both observational and modeling data to quantify how climate change and emissions from the largest 122 carbon producers have contributed to observed changes in regional water dynamics and explore the non-linearities underlying these relationships. Across the region, our findings show that climate change has reduced April snowpack by 44%, streamflow by roughly 16% and increased irrigation demand by 3.5%. Roughly half of these impacts are attributable to emissions traced to the Carbon Majors since 1950, translating to a nearly 18% reduction in snowpack, a 7% reduction in streamflow, and a 2% increase in irrigation demand. We also find a dramatic shift in the timing of warm season water availability, which occurs nearly two weeks earlier in some basins. Although this analysis focuses on the western United States, it reflects dynamics increasingly observed in arid and semi-arid agricultural regions worldwide, where climate change is intensifying competition over limited water resources. In total, our findings highlight the impact that emissions traced to only 122 corporations have had on water supply and demand across critical agricultural regions.