Impacts of Wildfire Severity and Other Related Factors on Hydraulic Conductivity.

Forest, woodland, and grassland watersheds throughout the world are major sources of high quality water for human use because of the nature of these soils to infiltrate, store, and transmit most precipitation instead of quickly routing it to surface runoff. This characteristic of these wildland soils is due to normally high infiltration rates, porosities, and hydraulic conductivities generated by biological and physical processes. Many of these ecosystems are subject to prescribed fires and wildfires that affect not only aboveground natural resources but also the soil and hydrologic systems. Undisturbed forest soils have an incredible range of K_sat (32 to >1,000 mm hr^-1). High severity wildfire can reduce K_sat to <14% of pre-burn conditions (e.g 510 to 69 mm hr^-1) or zero where strong water repellency develops. The main mechanisms affecting K_sat are soil properties (e.g. depth, texture, porosity, macropore development, etc.), vegetation, climate, geomorphology, and fire-related changes (e.g. development of water repellency, pore clogging with fine ash, and O horizon destruction). In some instances there are no changes in K_sat and in others K_sat increases have been observed. The general trend is a reduction in infiltration and increased surface runoff and flooding.