Quantifying the effect of surface sealing on post-fire runoff and erosion in the western U.S.

University Of Montana, Missoula MT

Investigators

Abstract

Wildfires can temporarily increase runoff and erosion rates in forested watersheds by several orders of magnitude, and these accelerated runoff and erosion rates have considerable geomorphic, ecological and societal significance. Surface sealing -- the formation of a thin surface layer with a very low hydraulic conductivity -- may contribute to increases in runoff and erosion after fire either through rainsplash induced compaction and disaggregation, the clogging of soil pores by ash, or the formation of low conductivity ash crusts. However, there has been very little work on the extent to which surface sealing contributes to increased runoff and erosion after fire, the sealing mechanisms involved, or the factors that contribute to an increased potential for sealing, and surface sealing effects have not been incorporated into predictive models of post fire runoff and erosion. This project will conduct an intensive, field and lab based research study to (1) determine the extent to which surface sealing contributes to increased runoff and erosion after wildfires in the western U.S.; (2) determine the various mechanisms of surface sealing and the factors that lead to an increased probability of seal formation; and, (3) develop a predictive model of the probability of surface sealing after fires, based upon the soil and ash properties in burned areas. The research will be based on six field and lab experiments. The work will result in quantitative, process-based understanding of post-fire surface sealing and new understanding of wildfire related runoff and erosion processes.