Science of Post Fire Flood and Erosion

The effects of wildfire on hydrologic regimes depends on burn severity, suppression decisions, topography, and the immediate post-fire precipitation regime. When fires destroy the vegetative canopy and remove litter, the amount of precipitation intercepted by plants and duff is reduced and more precipitation reaches the soil. Additionally, physical, chemical, and biological soil properties may experience significant changes due to soil heating. Not only do these changes impact the future productivity of the ecosystem, they can intensify hydrophobic conditions that limit infiltration of precipitation into soils. High severity burns can decrease the ability of soils to retain moisture and increase water repellency, causing precipitation to runoff rather than be absorbed. Reduced infiltration as a result of the hydrophobic layer leads to increased overland flow and causes the top layer to be easily eroded during significant precipitation events. Usually, erosion and debris flows are initiated by impacts from raindrops and overland flow in small and steep headwater basins, making these landscapes priorities for post-fire emergency response by managers, landowners, and communities.

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