PROGRESS IN SIMPLIFYING HYDROLOGIC MODELING PARAMETERIZATION AFTER A WILDFIRE PERTURBATION (Invited Presentation)

Wildfires create large-scale soil perturbations that lead to temporary, but drastic changes to soil hydrology and erodibility. These changes are often associated with sediment-laden floods and debris-flow hazards. Capturing the transfer of incoming rainfall to runoff is key to predicting debris-flow initiation and timing in burned areas. However, model simulations of overland flow rely on parameter estimates to simulate rainfall infiltration and water-flow velocity (primarily those that govern infiltration and flow roughness). Parameter estimation can be difficult to justify and can be calibrated only in cases where field observations are present. We present research that shows how parameters can be estimated for large burned regions through simple field measurements, obviating the need for complex parameter calibration techniques. Model results from this work demonstrate that it is possible to create overland flow simulations that perform well in burned areas with no adjustable parameters, which reduces efforts dedicated to parameter calibration. Our model produces unsteady, distributed overland flow that can be used to track flow depth and velocity throughout a rainstorm. This research shows how the hydrodynamic output from the model can be used to predict the location of debris-flow initiation, and the utility of this flow prediction as an input for debris-flow inundation models.