EXPECTED INCREASE IN POST-WILDFIRE DEBRIS FLOWS WITH CLIMATE CHANGE

Increasing area burned by wildfire and increasing intense precipitation events with predicted climate change will produce a significant increase in the number of post-wildfire debris flows in the western United States. Using a dataset of 50 fires and 355 individual debris-flow events, we show that climate change factors will increase both the probability of flows occurring and the volume of the events. The probability of a debris flow being generated from a burned watershed is affected by the increasing number and severity of storms triggering the flows. Conservative model interpretations show increased probabilities for a flow in an individual drainage basin by an average of 21%, with different climate scenarios ranging from 2% to 39%, by the year 2050. As fires increase in size due to climate change, a positive trend is also shown between the area burned and the number of debris flows generated. A predictive debris-flow volume equation for the Intermountain West is also influenced by factors that will be affected by climate change, and debris-flow volumes are calculated to increase with changing conditions by 4% to 52% over the next 35 years. The variability of both climate models and debris-flow predictive models prevent accurate prediction of number, probability, and volume of future debris-flow events, but the trends demonstrated by this data will help agencies and communities better anticipate and manage both hazards and risks.