Projected Effects of Climate Change on Post Wildfire Debris-Flow Hazards Applied to the 2017 Thomas Fire, California USA

¹ WW Wheeler & Associates, Inc., Englewood Colorado, USA
² Colorado School of Mines, Department of Geology and Geological Engineering, Golden Colorado, USA

Abstract

Climate changes are expected to increase the likelihood, volume, and overall hazard of post-wildfire debris flows, but it is a challenge to estimate specific changes and impacts from these hazards. In this study we use climate change models to modify the parameters in predictive equations to demonstrate changes for the 2017 Thomas Fire in California USA if a similar event were to occur in the years 2050 or 2075. Our results show that, based on changes in fire size, the number of burned drainage basins in 2050 would increase by 105% and by 2075 they would increase by 147%. Based on changes in fire size and rainfall effects, the overall volume of debris produced by debris flows would increase by 96% in 2050 and 147% in 2075. Finally, there would be a notable shift in hazard level towards basins classified as high hazard. The hazard models for the 2017 fire classified 54% of the drainage basins (937 total) as high hazard, but by 2050 there would be 60% (1869 total) classified as high hazard. By 2075, 67% of basins would be high hazard (2385 total). This represents an increase in high hazard drainage basins of 99% by 2050 and 155% by 2075. The results of this exercise indicate a substantial future increase in area impacted by post wildfire debris flows, the amount of debris produced, and the level of hazard posed.