Modeling post-fire flood and debris-flow hazards considering infrastructure sedimentation

While California has been known to experience a fire-flood cycle for about a century, post-fire flood and debris-flow risks are increasing due to increases in the frequency and intensity of wildfires and storms and urbanization in fire- and flood-prone areas. Existing models for estimating hazards to communities do not account for the filling of protective flood infrastructure with sediment during post-fire storms, which reduces capacity and can cause infrastructure clogging. We present an original model for estimating post-fire flood and debris-flow hazards that captures the interconnected influences of wildfire, storms, and reduced infrastructure capacity from sedimentation. The stochastic modeling approach can simulate present and future hazards to aid both short-term and long-term risk management efforts. Application of the framework to a hypothetical watershed representative of Southern California shows that the present-day compound hazard (considering post-fire erosion and infrastructure sedimentation) may be up to 6 times greater than the marginal hazard posed by peak flows in the absence of wildfire, and that future compound hazards could be up to 11 times greater than the marginal hazard based on future increases in wildfire frequency. 

Jong-Levinger (2023) Modeling post-fire flood and debris-flow Hazards considering infrastructure sedimentation, USGS Landslide Hazards Seminar, 14 April 2023