Impacts of Wildland Fires on U.S. Fresh Water Resources are Variable
Burning forests alter watershed hydrological cycles by modifying soil and forest cover properties. Researchers found that fires with moderate or high burn severity contributed most to increased river flows, but prescribed fires had little effect on water yield for large basins. Climate variability such as drought may mask the effects of wildland fire on water supplies, so effective forest management practices, such as prescribed burning, must consider local watershed conditions.
Today, 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 property, many fire effects only become evident with post-fire rainfall that results in floods, mud flows, and sedimentation in dam lakes. While these immediate impacts are obvious, risks to the continued availability of water supplies are less visible. Though forests and rangelands provide more than half of U.S. water supplies, the long-term impacts of fires, including wildfire and prescribed fire, on water supplies have not been measured nor factored into water management strategies. Researchers from the Eastern Forest Environmental Threat Assessment Center and partners developed a coupled wildland fire-water supply risk framework (known as FIWAS) to evaluate critical environmental thresholds for water resources across the contiguous United States. They discovered that wildland fires can enhance annual river flow in western regions with a warm temperate or humid continental climate, in the semi-arid Lower Colorado in particular. Most prescribed fires have a limited extent and low severity impacts; therefore, climate trends have a much greater impact on river flow where prescribed fires burn in the Southeast. These outcomes, published in the journal Nature Communications, help researchers evaluate the coupled wildland fire-water supply risk and contribute to sustainable land management plans for safeguarding future water resources.
Pictured: A prescribed fire burns in a southern forest. Photo by Dennis Hallema, USDA Forest Service.
Forest Service Partners/Collaborators: Southern Research Station
External Partners/Collaborators: Oregon State University, Joint Fire Science Program