[CaliforniaDisasters] Observed impacts of anthropogenic climate change on wildfire in California

Observed impacts of anthropogenic climate change on wildfire in California

A. Park Williams

John T. Abatzoglou

Alexander Gershunov

Janin Guzman‐Morales

Daniel A. Bishop

Jennifer K. Balch

Dennis P. Lettenmaier

First published: 15 July 2019

https://doi.org/10.1029/2019EF001210

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1029/2019EF001210

Abstract

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 five‐fold increase in annual burned area, mainly due to more than an eight‐fold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by 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 were 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 burned 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 non‐forest. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. 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.

Key Points

• Annual burned area in California increased five‐fold during 1972–2018, mainly due to summer forest fire
• Anthropogenic warming very likely increased summer forest fire by drying fuels. This trend is likely to continue
• Large fall fires are likely to become increasingly frequent with continued warming and possibly gradual declines in fall precipitation

View paper HERE: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019EF001210

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