Compound post-fire flood hazards considering infrastructure sedimentation

Flood and debris hazards are heightened following wildfires but are challenging to quantify due to interdependence between fire frequency and severity, peak flows during precipitation events, sediment loads, and sedimentation within infrastructure that reduces flow capacity. Herein we present a stochastic simulation framework to estimate compound flood and debris hazards from sequences of wildfires and rainstorms and the accumulation of sediment within flood infrastructure. Application of the framework to a hypothetical watershed representative of southern California shows that the present-day compound hazard may be up to six times greater than the marginal hazard posed by peak flows in the absence of wildfire, and that future compound hazards could be up to eleven times greater than the marginal hazard based on future increases in wildfire frequency. Numerous sensitivities are investigated, including infrastructure design and maintenance, which are shown to be crucial for moderating future increases in post-fire flood hazards.