Influence of natural and anthropogenic forcings on western US winter fire weather and the 2025 Los Angeles wildfires
- 1University of California Davis
- 2Lawrence Berkeley National Laboratory
- 3Lawrence Livermore National Laboratory
Abstract
Winter fire weather is shaped by interactions between anthropogenic climate change and natural climate variability, yet how the combination of human and natural forcings influences winter fire weather conditions remains poorly quantified. This study uses a multiple linear regression framework that removes long-term CO ₂ -related trends to examine the influence of natural modes of variability on the December–February monthly fire weather index over the western United States (WUS), with the January 2025 Los Angeles (LA) fire risk as a motivating case study. Results show that the El Niño Southern Oscillation (ENSO), Pacific North American pattern (PNA) and Atlantic Meridional Mode (AMM) significantly influence winter fire weather across the WUS, whereas the influence of CO ₂ is more pronounced and generally significant over the interior regions, but less evident along the coastal areas of the WUS. Positive phases of the PNA and AMM, combined with La Niña–like conditions during December 2024 and January 2025, significantly elevated fire weather risk across southern California, including LA County. The elevated fire-weather conditions preceding the January 2025 fires in LA and surrounding regions were aggravated by the combined influence of the natural and anthropogenic modes. Our study also shows that anthropogenic CO ₂ is associated with an estimated 10–20% increase in the chances of the 2024–25 fire weather over the WUS coastal states, although this contribution is not statistically significant, while La Niña and positive PNA significantly increase these chances by at least 20% across California and by more than twice across much of the WUS, including southern California and neighboring states. We find that large-scale natural climate modes combined with increases in greenhouse gas concentration provide valuable information for understanding and predicting WUS winter fire weather.
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BibTeX
@article{srivastava2026influence,
title = {{Influence of natural and anthropogenic forcings on western US winter fire weather and the 2025 Los Angeles wildfires}},
author = {Abhishekh Kumar Srivastava and Mark D Risser and Paul Ullrich and Michael Wehner},
journal = {Environmental Research Letters},
year = {2026},
month = oct,
doi = {10.1088/1748-9326/aeb710},
url = {https://iopscience.iop.org/article/10.1088/1748-9326/aeb710},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Influence of natural and anthropogenic forcings on western US winter fire weather and the 2025 Los Angeles wildfires
AU - Abhishekh Kumar Srivastava
AU - Mark D Risser
AU - Paul Ullrich
AU - Michael Wehner
PY - 2026
DA - 2026/10/21
JO - Environmental Research Letters
DO - 10.1088/1748-9326/aeb710
UR - https://iopscience.iop.org/article/10.1088/1748-9326/aeb710
AB - Winter fire weather is shaped by interactions between anthropogenic climate change and natural climate variability, yet how the combination of human and natural forcings influences winter fire weather conditions remains poorly quantified. This study uses a multiple linear regression framework that removes long-term CO ₂ -related trends to examine the influence of natural modes of variability on the December–February monthly fire weather index over the western United States (WUS), with the January 2025 Los Angeles (LA) fire risk as a motivating case study. Results show that the El Niño Southern Oscillation (ENSO), Pacific North American pattern (PNA) and Atlantic Meridional Mode (AMM) significantly influence winter fire weather across the WUS, whereas the influence of CO ₂ is more pronounced and generally significant over the interior regions, but less evident along the coastal areas of the WUS. Positive phases of the PNA and AMM, combined with La Niña–like conditions during December 2024 and January 2025, significantly elevated fire weather risk across southern California, including LA County. The elevated fire-weather conditions preceding the January 2025 fires in LA and surrounding regions were aggravated by the combined influence of the natural and anthropogenic modes. Our study also shows that anthropogenic CO ₂ is associated with an estimated 10–20% increase in the chances of the 2024–25 fire weather over the WUS coastal states, although this contribution is not statistically significant, while La Niña and positive PNA significantly increase these chances by at least 20% across California and by more than twice across much of the WUS, including southern California and neighboring states. We find that large-scale natural climate modes combined with increases in greenhouse gas concentration provide valuable information for understanding and predicting WUS winter fire weather.
SN - 1748-9326
ER -