Notable impact of wildfires in the western United States on weather hazards in the central United States

Abstract

Increased wildfire events constitute a significant threat to life and property in the United States. Wildfire impact on severe storms and weather hazards is another pathway that threatens society, and our understanding of which is very limited. Here, we use unique modeling developments to explore the effects of wildfires in the western US (mainly California and Oregon) on precipitation and hail in the central US. We find that the western US wildfires notably increase the occurrences of heavy precipitation rates by 38% and significant severe hail (≥2 in.) by 34% in the central United States. Both heat and aerosols from wildfires play an important role. By enhancing surface high pressure and increasing westerly and southwesterly winds, wildfires in the western United States produce stronger moisture and aerosol transport to the central United States and larger wind shear and storm-relative helicity in the central United States. Both the meteorological environment more conducive to severe convective storms and increased aerosols contribute to the enhancements of heavy precipitation rates and large hail. Moreover, the local wildfires in the central US also enhance the severity of storms, but their impact is notably smaller than the impact of remote wildfires in California and Oregon because of the lessened severity of the local wildfires. As wildfires are projected to be more frequent and severe in a warmer climate, the influence of wildfires on severe weather in downwind regions may become increasingly important.

Additional Information

© 2022 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY). This study is supported by the US Department of Energy (DOE) Office of Science Early Career Award Program (70017). We thank the resources of the National Energy Research Scientific Computing Center (NERSC). NERSC is a US DOE Office of Science User Facility operated under contract no. DE-AC02-05CH11231. Pablo Saide is thanked for providing scripts for producing QFED emissions. Y.W. and J.S. acknowledge support from the NSF grant AGS-2103714. The authors declare no competing interest.

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Published - pnas.202207329.pdf

Supplemental Material - pnas.2207329119.sapp.pdf

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