California on Fire: System Controlling State's Wildfires Has Been Overridden, and That's Bad News

The end of 2017 saw California set on fire, with over a million acres of land charred by what was the most destructive wildfire seasons the state had ever witnessed—a record that would be surpassed the following year.

"The last three years may be a harbinger of things to come," said Alan H. Taylor, a professor of geography at Pennsylvania State University and the lead author on a study looking at the climatic conditions that cause devastating fires across California. Findings show that a system normally involved in dampening wildfire seasons no longer has the same impact—and this shift, scientists say, appears to be here to stay.

The paper, published in PNAS, looked at fire activity across the state starting from 1600 A.D. through the present day. Researchers did this by examining jet-stream dynamics, specifically that of the North Pacific Jet (NPJ) stream, a high-altitude wind current that affects how much moisture hits California over the winter period.

The amount of snow and rain California receives in winter directly affects fire activity the following summer, so understanding the NPJ is important in predicting risk.

Taylor and his colleagues reconstructed the behavior of the NPJ over the last 400 years using paleoclimate data and climate models. From that, they were able to assess the impact it had on California fires.

Findings showed that before the start of the 20th century, a very specific pattern of precipitation extremes emerged. In years when the NPJ brought extremely wet conditions, wildfire rates were low. When the jet stream brought dry conditions, wildfire rates were high. Essentially, wet conditions reduced fire risk, while dry ones exacerbated it. The relationship was found to be constant over the 300 years.

However, after 1900 it changed, and NPJ precipitation levels started to separate from wildfire risk. "The winter of 2016-17 had a slightly stronger than normal jet, which, according to our results, in the past would have reduced fire risk," Taylor said in a statement. "Instead, we got a massive fire season in 2017.

"Between 1600 and 1903, there was not a single case of a high-precipitation year coupled with a high-fire year, as occurred in 2017."

The winter of 2017-2018 saw the NPJ bring extremely dry conditions—and the subsequent wildfire season became the most destructive and deadliest California had ever recorded, with more than 100 people killed. Close to 9,000 fires broke out, destroying more than 1.8 million acres of land. Jerry Brown, then the governor of California, linked the 2018 wildfire season to climate change, with the Sacramento Bee quoting him as saying the state must spend more to adapt to the "new abnormal" over the coming decades.

In the study, researchers said that if current fire management practices continued as they have been, the influence NPJ has on climate-fire relationships will be overridden. "Recent widespread fires in California in association with wet extremes may be early evidence of this change," they concluded.

Daniel Swain, a climate scientist from UCLA's Institute of the Environment and Sustainability who was not involved in the study, told Newsweek the findings provide an interesting insight into the links between climate and California's wildfires—as well as the implications of this for the future.

"One existing notion that this work strongly reinforces is that there is indeed a link between climate and wildfire," he said. "But also clear from this new research is the fact that modern 20th-century human land management interventions—especially the total suppression of the natural, low-intensity wildfires that used to regularly burn across the landscape—is also critically important.

"California has clearly experienced a massive uptick in large and extremely destructive wildfires in recent years, and many folks are looking for the singular cause. But it's increasingly looking like there isn't just one single reason for this shift toward more intense fire activity—it's really the net product of multiple factors all pushing the risk in the same direction."

Swain, whose work has focused on California's precipitation, said the findings are "a bit alarming" in terms of what it means for California's future. "The region has already experienced significant warming in recent decades, yet future warming is expected to be of an even larger magnitude than what we've experienced already," he said. "Because California's extreme forest fire years now appear to be 'uncoupling' from precipitation--it may not matter much whether California's average precipitation doesn't change much in the future, since extreme wildfire activity is increasingly being driven by vegetation aridity caused by elevated temperatures irrespective of precipitation levels."

This article has been updated to include comments from Daniel Swain.