Wildland fires are becoming more frequent, and in many cases they increase water yield from affected areas. A study by Forest Service scientists involving fires across the contiguous United States shows that areas within fire perimeters with moderate or high burn severity impacts contribute most to increased river flows.
There are more and larger forest fires compared to previous decades, and their impacts are devastating. In addition to the immediate threat to people and extensive property damage, many effects only become evident once it starts raining after the fire: floods, mud flows, and sedimentation in reservoirs—moreover, the continued availability of water supplies is at risk. One half of the surface freshwater used for drinking, irrigation, industry, hydropower, and recreation in the United States comes from headwater catchments located at a higher elevation. Eastern Forest Environmental Threat Assessment Center researchers used the coupled wildland fire-water supply risk framework (FIWAS) to evaluate critical environmental thresholds for water resources across the contiguous United States. They discovered that the moderate and high severity impact areas within fire perimeters can alter river flow if they cover at least one fifth of the upstream contributing area. In absolute terms, wildfires increase water supply most in the Pacific Northwest, but percentage-wise, in the Lower Colorado basin. In contrast, most prescribed burns have a limited extent and low severity impacts. Therefore, in the Southeast, climate trends have a much greater impact on river flow. These outcomes allow researchers to evaluate the coupled wildland fire-water supply risk, and design sustainable land management plans for safeguarding future water production.
Pictured: Large fires increased river flows for up to five years after a fire, even in areas with recurring drought. Cover image from USDA Forest Service General Technical Report SRS-238 (linked below).
Related publications:
Research Partners: Peter Caldwell and Yongqiang Liu, US Forest Service Southern Research Station.
External Partners/Collaborators: Kevin D. Bladon, Oregon State University. Joint Fire Science Program.
Contact: Dennis Hallema, Eastern Forest Environmental Threat Assessment Center, dennis.hallema@usda.gov.
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