Prescribed burns can decrease the severity of future fires by about 16 percent and slash smoke pollution by 14 percent, a new study has found.
These controlled blazes are much more effective outside the wildland-urban interface (WUI) — the area where homes meet wild vegetation — than within it, according to the study, published on Thursday in AGU Advances.
“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,” lead author Makoto Kelp, a postdoctoral fellow at Stanford University, said in a statement.
“It’s not a cure-all, but it’s a strategy that can reduce harm from extreme wildfires when used effectively,” Kelp added.
Experts already consider prescribed burns to be an effective strategy for curbing the threat of wildfires, the researchers acknowledged, noting that $2 billion in federal funds are allocated to such treatments.
Yet they also pointed out that the use of these controlled blazes across the U.S. West has only expanded slightly in recent years. This discrepancy, they surmised, could be due to the lack of research quantifying the practice’s effectiveness and mixed public opinions on the matter.
To enumerate the benefits of the burns, the scientists used high-resolution satellite imagery, land management records and smoke emission inventories to compare outcomes of treated and untreated areas in the extreme 2020 fire season.
Specifically, they focused on places treated with controlled fire between late 2018 and spring 2020 and at adjacent untreated zones.
Their analysis ultimately showed that areas treated with prescribed fire burned less severely and generated much less smoke. That finding was particularly important to the authors, who stressed that fine particulate matter (PM 2.5) emitted by wildfires has been linked to cardiovascular and respiratory issues.
“Smoke is a silent and far-reaching hazard, and prescribed fire may be one of the few tools that actually reduces total smoke exposure,” co-author Marshall Burke, an associate professor of environmental social sciences at Stanford, said in a statement.
Meanwhile, the scientists found that controlled burns produce only about 17 percent of the PM 2.6 smoke that would result from a wildfire in the same area.
They estimated that if California achieved its goals of treating a million acres with prescribed fire annually, the Golden State could slash PM 2.5 emissions by 655,000 tons over five years. That quantity would be equivalent to 52 percent of the total smoke pollution generated during California’s 2020 wildfire season, according to the study.
As far as the different effects in WUI and non-WUI zones are concerned, the authors found that prescribed burns led to an 8.5 percent drop in fire severity in the former and a 20 percent decline in the latter.
In WUI zones, they noted, agencies usually opt for mechanical thinning over prescribed burns due to smoke and safety concerns.
Although the researchers could not yet offer an explanation behind the discrepancy, they said that gaining further insight into the matter would be critical.
Senior author Noah Diffenbaugh, a professor at Stanford’s Doerr School of Sustainability, noted the rapid population growth in WUI areas, where plants are “most sensitive to climate-induced intensification of wildfire risk.”
As such, he stressed that understanding why prescribed burns are less effective in these areas “is a key priority for effectively managing that intensifying risk.”