Controlled Burns Cut Wildfire Smoke by 14%

Prescribed burns can reduce wildfire severity by 16% and cut smoke pollution by an average of 14%, according to a Stanford-led study published in AGU Advances.

The research provides the first comprehensive evidence that controlled burning works in practice across the western United States, analyzing satellite data from 186 burn sites that later experienced wildfires during the catastrophic 2020 fire season.

“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 at Stanford’s Doerr School of Sustainability. The findings come as nearly $2 billion in federal funding has been allocated for hazardous fuel reduction treatments.

Real-World Fire Strategy Analysis

Using high-resolution satellite imagery, land management records, and smoke emissions data, researchers compared areas treated with prescribed fire between late 2018 and spring 2020 to adjacent untreated areas. Both zones later burned during 2020’s extreme fire season, allowing scientists to measure the protective effects of controlled burns.

The study addressed a critical knowledge gap. While experts have long considered prescribed burns effective, little research existed to quantify their benefits, and public opinion remains mixed due to concerns about smoky air and escaped fires.

Key Findings

The analysis revealed several important patterns:

• Prescribed fires produced only 17% of the smoke that wildfires generate in the same areas
• Fire treatments worked better in forests than shrublands or barren areas
• Controlled burns significantly outperformed mechanical thinning at reducing fire severity
• Treatments were less effective in wildland-urban interface zones where homes meet wildland vegetation

In wildland-urban interface areas, fire severity dropped by just 8.5%, compared to 20% in areas away from human development. This difference reflects the cautious approaches agencies must adopt near populations and infrastructure, despite these zones being a policy priority.

Smoke Pollution Benefits

“People often think of wildfires just in terms of flames and evacuations,” explained Marshall Burke, an associate professor at Stanford. “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.”

Fine particulate matter from wildfires has been linked to respiratory and cardiovascular problems and increasingly drives poor air quality across the country. The researchers estimate that if California met its goal of treating one million acres annually with prescribed fire, it could cut particulate matter emissions by 655,000 tons over five years—equivalent to more than half the total smoke pollution from the state’s devastating 2020 wildfire season.

Policy Implications

The study’s quasi-experimental design addressed concerns about smoky air from prescribed burning. While controlled burns do produce smoke, the research shows they create a net benefit by preventing much larger emissions from future wildfires.

“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,” noted Noah Diffenbaugh, a Stanford climate scientist and study co-author. “So, understanding why the prescribed fire treatments are less effective in those areas is a key priority for effectively managing that intensifying risk.”

California currently treats only about 30,000 acres annually with prescribed fire through CAL FIRE—just 7.5% of its stated goal of 400,000 acres by 2025. The state’s broader objective calls for treating one million acres annually across all agencies and organizations.

Study Limitations and Future Research

The researchers acknowledge their findings likely represent conservative estimates of prescribed fire benefits, as treatments can have protective spillover effects on surrounding untreated areas. The analysis focused on fires occurring within two years of prescribed burns, but longer-term benefits could be even greater.

The study also highlighted the complexity of implementing effective prescribed burns near populated areas, where mixed approaches and cautious protocols may reduce treatment effectiveness despite being necessary for safety.

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