Wildfires and climate change

San Francisco, California; mid-day on September 9, 2020 (Stephen Lam/Reuters)
Golden Gate Bridge, San Francisco, CA; 9 a.m., September 9, 2020 (Drew Tuma, Twitter)

There is a direct connection between wildfires in the western United States and climate change.

Featured article:

Park Williams, A., Abatzoglou, J. T., Gershunov, A., Janin Guzman‐Morales, Bishop, D. A., Balch, J. K., & Lettenmaier, D. P. (2019). Observed impacts of anthropogenic climate change on wildfire in California. Earth’s Future, 7(8), 892-910. [PDF] [Cited by]

“Recent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming (very likely driven by drying of fuels promoted by human‐induced warming). Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful. Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire; warming effects were also apparent in the fall by enhancing the odds that fuels are dry when strong fall wind events occur. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California’s diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date. Human‐caused warming has already significantly enhanced wildfire activity in California, particularly in the forests of the Sierra Nevada and North Coast, and will likely continue to do so in the coming decades.

See also —

Smoke from wildfires causes health problems

Climate change and wildfire in California

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