NAU study projects large base-flow losses in western U.S. headwaters

Northern Arizona University researchers report that groundwater-fed streamflow, or base flow, has declined across western U.S. headwater watersheds since 1950 and could fall by 45% to 65% by the end of this century if current climate trends continue, phys.org reported. The study appears in Earth's Future (DOI: 10.1029/2025ef007971). The team analyzed 75 years of streamflow data from 115 headwater basins across 11 Western states and used machine learning models to project conditions under multiple climate scenarios, including SSP2-4.5 and SSP5-8.5. Researcher Caelum Mroczek said headwater streams make up nearly 88% of the western U.S. river network, and that under a high-emissions path some of the most vulnerable systems could see the greatest relative losses, amounting to millions of acre-feet of water. The authors urge better monitoring in headwaters to manage future water resources as earlier runoff and weaker summer flows reshape supplies fed by small mountain streams.