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Projected climate changes in post-wildfire debris-flow likelihood, volume, and runout applied to the 2017 California Thomas Fire
White, Zane C.
White, Zane C.
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2021
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Abstract
Using current post-fire debris-flow models of the 2017 California Thomas Fire, created by the United States Geological Survey (USGS), this research intends to show the effects of climate change on fire size, fire severity, and rain intensities as well as post-fire debris-flow likelihood, volume, hazard, and runouts. This research aims to provide answers to the following research questions:1. How would projected future climate conditions affect post-fire debris-flow likelihood, volume, runout, and combined hazard were the California 2017 Thomas Fire to occur in the years 2050 and 2075?
2. How can these results be projected to the (south)western United States in terms of post-fire debris flows?
3. How will this research aid in debris-flow prediction and management under climate change conditions?
Using available data and technical literature values, fire size, fire severity, and design storm rain intensities were projected to the years 2050 and 2075. Three sets of models were created to show the changes in the Thomas Fire under climate change. The first set of models kept the fire conditions of the Thomas Fire the same but included scaled rainfall intensities. These models accounting for rainfall intensity changes show an increase in high-hazard basins of approximately 12% by 2050 and 14% to 18% by 2075 when compared to 2017. The second set of models use the estimated volumes of debris flows to generate 36 runout inundation models. The runout models show an increase in debris-flow inundation with increasing rainfall intensity in the future, mostly in the form of longer runout paths. The last set of models incorporates increases in fire size, fire severity, and rain intensity. The 2050 model predicts 6% more high-hazard basins, and the 2075 models predict 10% to 13% more high-hazard basins when compared to 2017.
Implementing climate change projections into the post-fire debris-flow likelihood and volume calculations resulted in increased hazard and runout for all models. The results of this project, in combination with the background information, show that climate change will increase post-fire debris-flow hazards and inundation in the western United States.
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