Selection of Parameters Values to Model Post-fire Runoff and Sediment Transport at the Watershed Scale in Southwestern Forests

摘要

Erosion and runoff have been observed to increase following fire. Land managers and Burned Area Emergency Rehabilitation (BAER) teams must be able to estimate these post-fire changes. Studies of post-fire erosion on burned watersheds show that the concentrations of sediment eroded from burned rangeland and forested hillslopes in the southwestern United States can be extremely high. Since wildfire primarily impacts soils and vegetation cover on hillslopes, it is appropriate to assume that changes in hillslope conditions will result in changes in runoff peak, volume and sediment yield. The AGWA (Automated Geospatial Watershed Assessment) hydrologic modeling tool employs both an empirical model (SWAT) and a more process-based model (KINEROS2). In order to study how these models should be modified to provide land managers with a means to assess the impact of fire, the models were applied on two burned watersheds. Analysis of data from the Marshall Gulch watershed near Tucson, Arizona, indicates that changes in runoff volume are small compared to changes in peak runoff. The application of the KINEROS2 model to burned conditions at the Starmer Canyon near Los Alamos, New Mexico shows a pattern of change over time that is consistent with watershed recovery. Calibrated hillslope roughness values are consistent with independent estimates for roughness under bare conditions following the fire to roughness consistent with forested conditions three years later. The modeling also indicated that increasing hillslope roughness over time accounts for much of the change in runoff response.