California, and the world at large, will contend with longer, hotter, drier wildfire seasons

Climate change is going to put California at risk of longer, more dangerous, and more destructive wildfire seasons reports a new study from the Stanford School of Earth, Energy & Environmental Sciences

Australian wildfire photographed in 2019.
Image credits Sippakorn Yamkasikorn.

The authors hope their work will guide authorities to implement more effective strategies for wildfire risk mitigation and land management, as well as to spur better resource allocation for the fighting of wildfires.


“Many factors influence wildfire risk, but this study shows that long-term warming, coupled with decreasing autumn precipitation, is already increasing the odds of the kinds of extreme fire weather conditions that have proved so destructive in both northern and southern California in recent years,” said study senior author Noah Diffenbaugh, the Kara J Foundation professor at Stanford’s School of Earth, Energy & Environmental Sciences.

The team reports that autumn days with weather conditions conducive to extreme fires have doubled in frequency since the early 1980s in California, while rainfall during the wildfire season has dropped by about 30%. At the same time, the average temperature has risen by over 2 degrees Fahrenheit (more than 1 degree Celsius) over the same timeframe, with late summer and early autumn showing the highest increases. All in all, these factors work together to create very dry plant material in forests and grasslands that can act as tinder during the same parts of the year when dry “Diablo” and “Santa Ana” winds blow throughout northern and southern California.

This is what has been feeding the large and fast-spreading wildfires seen across the state in recent years, the team explains. And their effect has been seen over the past few years: California recorded its deadliest wildfire, its two largest wildfires, and its two most destructive wildfires so far during 2017 and 2018, the team explains, which collectively caused more than $50 billion in damage and claimed over 150 lives.

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Map of 2017 California wildfires from January 1 to October 11.
Image credits Wikimedia.

The paper analyses the November 2018 Camp Fire in the Northern Sierra Nevada foothills and the Woolsey Fire around the same time near Los Angeles. Both were fueled by strong seasonal winds and dry plant material created during the state’s hottest summer on record (in 2018). The outcomes of the fire were worsened due to the state’s limited emergency response resources, which were put under immense strain trying to contain the fires raging across different areas.

Local data, global problem

For the study, the team looked at historic temperature and rain gauge records to determine the risk of extreme wildfires throughout the year. Autumn showed an especially pronounced increase, with a doubling in conditions that foster such events over the past four decades. A suite of climate model simulations showed that human-caused climate change is at the root of this change in conditions.

“Autumn is of particular concern since warmer, drier conditions may coincide with the strong offshore wind events which tend to occur in the September to November period,” said Michael Goss, the study’s lead author and a postdoctoral scholar in Diffenbaugh’s Climate and Earth System Dynamics Group.

As for solutions, the team showed that the proposed reductions in emissions under the United Nations’ Paris agreement would help to slow down the rate at which wildfire risks increase — however, even in this scenario, much of California will likely still experience a rise in extreme wildfires in the future. The findings are “yet another piece of evidence that climate change is already having a discernible influence on day-to-day life in California,” according to Daniel Swain, a research fellow at UCLA, the National Center for Atmospheric Research and The Nature Conservancy, a study coauthor.

While the study focused on California, the findings are broadly applicable to any regions that are historically fire-prone, the team explains. This further exacerbates the problem, as global firefighting resources need to be spread over a larger area, limiting their effectiveness.

Apart from curbing our emissions, the team recommends controlled burning to reduce available fuel, upgrades to emergency communications and response systems, the development and implementations of community-level protective fire breaks, and changes to zoning and building codes meant to promote fire-resistant construction.

The paper “Climate change is increasing the risk of extreme autumn wildfire conditions across California” has been published in the journal Environmental Research Letters.

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