Fact Sheet: Sediment Yield After Severe Wildfire

Wildfires throughout the western U.S. have increased in size and severity as a result of 20th century land use practices including fire suppression, which has elevated risks to communities bordering and downstream of forested watersheds. High-severity wildfire (i.e., where most trees are killed) in the arid and semi-arid Southwest changes watershed response to precipitation, mainly by increasing runoff. This results in a high risk of flooding, sediment transport, and erosion, particularly on steep slopes (DeBano et al. 1998). Forest floor materials such as organic matter and dead leaves normally absorb most precipitation and limit runoff, but severe fire eliminates this forest floor cushion, leaving a slick, sometimes water resistant surface that deflects a significant amount of rain, or runoff. Slope stability is compromised by loss of herbaceous cover. The increased runoff combined with the reduced slope stability creates an optimal environment for sediment mobilization from hillslopes (also known as hillsides) and channels, erosion, and flooding. This fact sheet summarizes significant findings on sediment transport and erosion on burned landscapes in semi-arid systems with ponderosa pine and mixed conifer type vegetation