Study shows controlled burns can reduce wildfire intensity and smoke pollution

(Press-News.org) As wildfires increasingly threaten lives, landscapes, and air quality across the U.S., a Stanford-led study published in AGU Advances June 26 finds that prescribed burns can help reduce risks. The research reveals that prescribed burns can reduce the severity of subsequent wildfires by an average of 16% and net smoke pollution by an average of 14%.

“Prescribed fire is often promoted as a promising tool in theory to dampen wildfire impacts, but we show clear empirical evidence that prescribed burning works in practice,” said lead author Makoto Kelp, a postdoctoral fellow in Earth system science at the Stanford Doerr School of Sustainability. “It’s not a cure-all, but it’s a strategy that can reduce harm from extreme wildfires when used effectively.”

Experts consider prescribed burns an effective strategy to reduce the threat of wildfires, and nearly $2 billion of federal funding had been set aside to conduct these and similar treatments to reduce hazardous fuel. Still, the use of prescribed burning in western states has expanded only slightly in recent years. Little research exists to quantify its effectiveness, and public opinion remains mixed amid concerns that prescribed burns can lead to smoky air and escaped fires.

Data-driven fire strategy

At Stanford, Kelp is working with climate scientist Noah Diffenbaugh and environmental economist Marshall Burke through the National Oceanic and Atmospheric Administration Climate and Global Change Postdoctoral Fellowship Program. Using high-resolution satellite imagery, land management records, and smoke emissions inventories, the research team compared areas treated with prescribed fire between late 2018 and spring 2020 to adjacent untreated areas that both later burned in the extreme 2020 fire season. The analysis found that areas treated with prescribed fire burned less severely and produced significantly less smoke.

That finding is particularly important given the growing recognition of wildfire smoke as a major public health threat. Fine particulate matter (PM2.5) from wildfires has been linked to respiratory and cardiovascular problems and is increasingly driving poor air quality across the U.S.

“People often think of wildfires just in terms of flames and evacuations,” said Burke, an associate professor of environmental social sciences in the Doerr School of Sustainability. “But the smoke is a silent and far-reaching hazard, and prescribed fire may be one of the few tools that actually reduces total smoke exposure.”

Not all treatments are equal

The study also highlights a key nuance: the authors found that prescribed fires were significantly more effective outside of the wildland-urban interface (WUI)—the zones where homes meet wildland vegetation—than within it. In WUI areas, where agencies often rely on mechanical thinning due to concerns about smoke and safety, fire severity was reduced by just 8.5%, compared to 20% in non-WUI zones.

“We already know that population is growing fastest in the areas of the wildland-urban interface where the vegetation is most sensitive to climate-induced intensification of wildfire risk,” said Diffenbaugh, the Kara J Foundation Professor in the Stanford Doerr School of Sustainability and the Kimmelman Family Senior Fellow at the Stanford Woods Institute for the Environment. “So, understanding why the prescribed fire treatments are less effective in those areas is a key priority for effectively managing that intensifying risk.”

Smoke tradeoffs and policy implications

The study addresses concerns about smoky air from prescribed burning, finding that the approach produces only about 17% of the PM2.5 smoke that would be emitted by a wildfire in the same area. The researchers estimate that if California met its goal of treating one million acres annually with prescribed fire, it could cut PM2.5 emissions by 655,000 tons over five years—more than half of the total smoke pollution from the state’s devastating 2020 wildfire season.

The authors note that their findings likely represent a conservative estimate of the benefits of prescribed fire, as such treatments can have protective spillover effects on surrounding untreated areas.

“This kind of empirical evidence is critical for effective policy,” said Kelp. “My hope is that it helps inform the ongoing conversation around prescribed fire as a potential wildfire mitigation strategy in California.”

 

Coauthors of the study also include Minghao Qiu of Stony Brook University, Iván Higuera-Mendieta, a PhD student in Earth system science at Stanford; and Tianjia Liu of the University of British Columbia.

Burke is also a senior fellow at the Stanford Woods Institute for the Environment, the Freeman Spogli Institute for International Studies, and the Stanford Institute for Economic Policy Research (SIEPR); an associate professor (by courtesy) of Earth system science; and a member of Bio-X and the Wu Tsai Neurosciences Institute.

The study was funded by the National Oceanic and Atmospheric Administration and Stanford University.

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