Flood risk modeling and field verification for post-wildfire Arizonan watersheds in annual and decadal time series

Background Wildfires can cause significant hydrologic impacts on watersheds. The immediate and long-term impacts of wildfires are especially concerning at the wildland–urban interface (WUI). Aim This research aims to combine multi-decadal observations and modeling in two high-elevation Arizona, USA, watersheds impacted by the 1977 Radio Fire and the 2019 Museum Fire to determine if heightened flood risk persists. Methods Hydrologic modeling, including both Soil Conservation Service (SCS) curve number (CN) and Green and Ampt (GA) estimations for rainfall losses, and extensive empirical observations were utilized in this study on two burned watersheds characterized by predominantly ponderosa pine (Pinus ponderosa) forest. Key results Results of the modeling and observations indicate that the immediate post-wildfire peak flow is between 6 and 14 times higher than pre-disturbance and that long-term vegetation shifts can lead to increased flood risk (two to three times the pre-fire flows) even 10 or more years after the fire. Conclusions Increased flood risk after a fire can persist for multiple decades, creating the need for long-term flood risk planning, especially near the WUI. Implications The results of this study can help inform those tasked with flood risk management of the long-term impacts of wildfires near the WUI.