High-Resolution Historical and Future Assessments of U.S. Wildfire Potentials

Emily Brown, SULI student

Recent extreme wildfire seasons in the western US have caused severe disruptions in utility infrastructure, and led to substantial economic costs and social stresses. There is a great concern that a new climatic equilibrium will result in a long-term increase in the frequency of wildfires. This project calculates one of the most commonly used fire indices (Keetch-Byram Drought Index, KBDI) to establish a scientific approach to assessing future potential fire activity under climate change.  First, we calculated KBDI for the contiguous United States using high resolution (4-km), high quality observation data (Parameter elevation Regression on Independent Slopes Model, PRISM) for the last 40 years (1978-2017). This dataset demonstrates geographical and seasonal variations in the estimated fire danger potential based on the weather conditions over the US; then the KBDI from our high resolution Weather Research and Forecast (WRF) model is calculated for both historical and future time periods. The WRF-based KBDI shows similar spatial distributions and temporal trends compared with the PRISM-based KBDI but underestimates the fire indices over the low fire risk regions and seasons. Future projections under RCP8.5 show that there is an increase in the number of days with high fire index by the mid and end of 21stcentury; the time with high fire index is shifting to earlier dates; and the annual peak of fire index is getting larger. We found that the increase of daily maximum temperature is the major contributor to the increase of KBDI, as opposed to changes in precipitation.

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