Adverse Hydrologic and Ecologic Impacts of Wildfires in Western Watersheds

摘要

Wildfire is a common occurrence in the semi-arid western and southwestern United States. Extended periods of drought increase the probability and severity of wildfires. The destruction of vegetation and ground litter and altered soil conditions adversely impact the hydrologic response of the watershed by increasing the runoff during post-wildfire rainfall events. The higher peak flows and greater soil erosion potential, in turn, lead to accelerated soil erosion, debris flows, and slope failures. Sediments transported to downstream waters have the potential to accentuate flooding, cause sedimentation, and change channel morphology. In addition, the sediments act as a vector for transport and redistribution of contaminants to downstream waters that may be detrimental to aquatic ecosystems. The severity of post-wildfire flooding and damage depends upon the severity of the burn, the nature of the burned vegetative cover, topography, geology, soil conditions, the timing and intensity of post-wildfire rainfall events, watershed recovery, proximity of structures to flooding sources, and engineered mitigation measures. The influence of some of the above factors is examined for the La Canada Flintridge - La Crescenta area in Southern California, which was affected by three major fire-flood sequences in the past century.