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Abstract Wildfires pose a significant threat to human society as severe natural disasters. The western United States (US) is one hotspot that has experienced dramatic influences from autumn wildfires especially after 2000, but what has caused its year‐to‐year variations remains poorly understood. By analyzing observational and atmospheric reanalysis datasets, we found that the West Pacific (WP) pattern centered in the western North Pacific acted as a major climatic factor to the post‐2000 autumn wildfire activity by inducing anomalous high pressure over the western US via teleconnections with increased surface temperature, decreased precipitation, and reduced relative humidity. The WP pattern explains about one‐third of the post‐2000 years‐to‐year variance of the western US autumn wildfires. These effects were found to be much weaker in the 1980–1990s, as the active region of WP‐associated high pressure was confined to the eastern North Pacific. Such eastward shift of the WP teleconnection pattern and its resultant, enhanced influence on the weather conditions of western US autumn wildfire after 2000 are also captured by the sea surface temperature (SST)‐forced atmospheric model simulations with the Community Atmosphere Model version 6 (CAM6). The CAM6 ensemble‐mean changes in the WP teleconnection pattern at 2000 is about half of the observed changes, which implies that external radiative forcing and/or SST changes have played an important role in the WP pattern shift. Our results highlight a pressing need to consider the joint impacts of atmospheric internal variability and externally forced climate changes when studying the interannual variations of wildfire activity.
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Notable impact of wildfires in the western United States on weather hazards in the central United States
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 ( 1 ) stronger moisture and aerosol transport to the central United States and ( 2 ) 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.
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- Award ID(s):
- 2103714
- PAR ID:
- 10414739
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 44
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1073/pnas.2207329119
