When data scientist Xaio Wu arrived at Stanford University for his postdoctoral fellowship, California was coming off a record-breaking wildfire season. In 2020, nearly 9,900 fires burned more than 4.3 million acres of land in the state, killing dozens of people and causing billions of dollars worth of damage.
That motivated Wu and his colleagues to figure out how they could use their skills to help prevent future disasters. One area they want to look closely at is prescribed burning, which is the deliberate use of controlled fires to help clear natural debris, vegetation and other fuels. If allowed to accumulate unchecked in forests, this debris can fuel massive, uncontrollable fires, such as the devastating Camp Fire, which burned the city of Paradise, California, in 2018.
Prescribed burning is not a new tool. Indigenous peoples have been using this method of forest management for centuries, and it has seen a resurgence in recent years, as climate change makes fires more frequent and intense and the state-led policies of “total fire suppression” were questioned. To better quantify the effects small fires can have on preventing large ones, Wu and his colleagues compiled and analyzed 20 years of California wildfire data.
Researchers have classified thousands of fires based on the amount of energy they release, which can be obtained from satellite data. And, in a study published Friday in the academic journal Advances in Sciencethey published some of the strongest evidence that low-intensity fires can significantly reduce the risk of high-intensity fires that are often the most destructive.
“Transitioning from after-the-fact firefighting to proactive use of natural fire will strengthen forest resilience.”
“This research is larger than most previous research,” said Patrick Gonzalez, a forest ecologist at the University of California, Berkeley, who was not involved in the study.
Wu, who is now an assistant professor of biostatistics at Columbia University, and his co-authors found that the chances of a high-intensity fire decreased by 64 percent in the first year after a low intensity of the fire. Low-intensity fires provide some degree of protection for at least six years in total.
“It adds numbers to concepts that people already understand,” said Lenya Quinn-Davidson, director of the University of California Agriculture and Natural Resources’ Fire Network. “Having that kind of quantification is very helpful.”
While only a fraction of the fires in the study’s dataset were actually prescribed, Wu explained that the protective effect seen in low-intensity fires provides empirical support for controlled burns as a tool for forest management.
“This indicates that there is a lot of benefit in increasing the scale of prescribed burning in California,” Wu said, noting that the state has a goal of “spreading beneficial fire” to 400,000 hectares annually by 2025. Gonzalez and Quinn-David agree—and add that the study also supports lighting wildfires in remote areas.
“When wildfires burn under moderate conditions, we get the same effects as we would with a prescribed fire,” he said. He added, “the transition from after-the-fact fire fighting to active use of natural fire will strengthen forest resilience and reduce catastrophic fires under changing climate.”
Going forward, Wu wants to expand his work in science and geography. For example, he wants to also research the potential risks of prescription burns—such as air pollution—so that policymakers can weigh them against the benefits. And, with wildfires becoming a growing threat around the world, he said, “We really want to expand this research to other areas of the United States and around the world.”
Applying this study’s methodology elsewhere would require acquiring and integrating new data sets, Wu said, and the results would not necessarily be the same. The mostly conifer forests studied by the California researchers naturally burn regularly but at a lower intensity, which may not occur in other landscapes. But Wu believes the general pattern is likely to continue.
“The magnitude and duration (of protection) will be influenced by many factors,” he said. “(But) we continue to hold that prescription burns help prevent fires.”