Post-wildfire sediment source and transport modeling, empirical observations, and applied mitigation: an Arizona, USA, case study

Abstract. Post-wildfire floods are receiving greater attention as wildland–urban interfaces become more common and catastrophic wildfires have increased in frequency. Sediment sourcing, transport, and deposition in the post-wildfire environment receive attention due to the severity of risk caused by debris flows and concentrated sediment flood flows. This study compares sediment model predictions based on the Modified Universal Soil Loss Equation (MUSLE), the Watershed Assessment of River Stability and Sediment Analysis (WARSSS) suite of models, and the free internet-based WEPPcloud post-wildfire sediment model for the 2019 Museum Fire (809 ha of steep slope Pinus ponderosa forest on a series of basaltic domes). Empirical evidence from four floods in 2021 indicated 9900 Mg of sediment yield to city of Flagstaff neighborhoods, WEPPcloud estimated 3870 Mg yr−1, MUSLE predicted 4860 Mg yr−1 (based on the four events), and the WARSSS suite of models predicted 4630 Mg yr−1. Both the Watershed Erosion Prediction Project (WEPP) and WARSSS estimated more sediment yield from channels than hillslope (51 %/49 % and 60 %/40 %, respectively) though the spatial patterns differ between the models. The utility of sediment forecasting to inform the application of sediment mitigation structures to help reduce downstream impacts of post-wildfire water and sediment flows is discussed. Continued revisions of sediment forecasts, based on case studies such as this one, can provide researchers, managers, and policymakers with tools for ecological and human risk mitigation and emergency management.