Mounting damage and losses in the United States from post-wildfire flash floods and debris flows

Considerable progress has been made in forecasting the likelihood, magnitude, and mobility of post-wildfire flash floods and debris flows; however, we lack systematic observations of the physical and financial effects of these hazards, which can be used to close gaps between scientific understanding of the hazard and risk reduction. Here, we introduce a 147-year (1879–2025) inventory of damage and losses associated with post-fire flows in the United States. These observations enable an assessment of the geographic convergence and frequency of damaging post-fire flow events, as well as their multi-asset damage profiles and loss distributions. We find that the long-term (1879–2025) mean annual frequency of damaging flow events is greater than one and that recent (2016–2025) fatality rates and levels of monetary loss appear higher compared to historical periods. Our study provides an empirical baseline that can be used for long-term hazard planning amid global pressures compounded by wildland-urban interface expansion, increased wildfire activity, and rainfall intensification.