Abstract
Recent increases in western United States wildfire activity are raising concerns for regional water supplies. Analyzing the wildfire histories (1940-2024) of 3,100 watersheds, we identify a significant regime shift in the late 20th century. Watersheds with higher runoff ratios, critical for regional water provisioning, have significantly increasing burn area trends. The burned areas double following the late 20th century changepoints. Analysis of 17,000 watersheds reveals a diverging fire regime: a transition from moderate burns (1-20% area) towards minimal (<1%) and extensive (> 20%) events. Vulnerability is greatest in forested and mountainous regions, specifically those providing water to 100,000 or more downstream consumers. An integrated watershed management approach, one that considers land management and downstream water operations, may help secure water supplies and mitigate the cascading hazards from wildfire.
Acknowledgements
We are grateful to J. Wagenbrenner, V. Espinoza, A.M. Lopez, and B.A. Wilder for discussions that contributed to this work. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Funding
The authors disclose support for the research of this work from NASA [grant number 80NSSC24K0297]. A.M.K. and B.B.M. disclose partial support from the SDSU 2024 Postdoctoral Fellow Program. C.M.L. discloses that a portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).
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Karto, D.J., Martinez, B.B., Lee, C.M. et al. Diverging wildfire regimes and doubling of burn area in western United States water supply watersheds.
Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03909-x
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DOI: https://doi.org/10.1038/s43247-026-03909-x
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