Prescribed burns are important for land management and preventing wildfires, but a new study finds these managed fires are also significant contributors to air pollution in the southeastern United States - particularly in areas with large minority and low-income populations. The study also finds these air quality impacts could become more pronounced in the decades ahead as the effects of climate change become more pronounced.
The term "prescribed burns" refers to activities where sections of land are intentionally burned to clear undergrowth, reduce the risk of wildfire, manage land for wildlife, and so on.
"However, smoke from prescribed burns can also pose challenges to air quality," says Fernando Garcia-Menendez, corresponding author of a paper on the work and an associate professor of civil, construction and environmental engineering at North Carolina State University. "And climate change may reduce the number of days when it is possible to conduct a prescribed burn, due to meteorological conditions such as high temperatures, drought or high winds."
"Given these concerns and given how important prescribed burns are to land management in the southeastern United States, we wanted to get a better understanding of how these burns affect air quality in the Southeast now - and how they may affect air quality in the future," says Megan Johnson, first author of the paper and a Ph.D. graduate from NC State.
For this study, researchers drew on air quality and emissions data from federal databases for the year 2018, including the number and location of prescribed burns in southeastern states, as well as data from previously published climate change projections. In addition, the researchers conducted a survey of 223 land managers in the Southeast to learn more about how meteorological conditions affect their decisions about prescribed burns and how they think climate change may affect their ability to conduct prescribed burns in the future.
The researchers then fed these data into a complex computational model that allowed them to both capture how prescribed burns affected air quality in 2018 and to project how the burns would likely affect air quality between 2055 and 2059.
"In order to understand how burns and climate may affect air quality in the future, first you need to establish how burns are affecting air quality now," says Garcia-Menendez. "And we found that, across the Southeast, prescribed burns account for 5-10% of particulate matter (PM2.5) air pollution annually - which is significant.
"However, prescribed burns account for 15-25% of PM2.5 pollution in areas with the most prescribed burns - which are clustered in the region where Alabama, Florida and Georgia meet," Garcia-Menendez says.
"The areas with the highest levels of smoke are home to around two million people, and these populations have higher fractions of people of color and people with low incomes relative to both the regional average and to the populations experiencing the least smoke," says Johnson.
"Right now, these regions are not violating air quality standards for PM2.5. But we found that climate change may make it difficult for these areas to comply with those standards in the future."
The researchers found that climate change may affect smoke (and air quality impacts) from prescribed burns in multiple ways. One major factor is that if there are fewer days when land managers can conduct prescribed burns, it is likely that more burns will be conducted on the viable days. Similarly, land managers are more likely to burn large areas of land at once, rather than burning several small areas over time.
"Whether it's more burns, larger burns, or both, you're putting more smoke into the air on a given day, which means a lot of PM2.5 being put into the air at once," says Johnson.
What's more, the viable days for conducting a prescribed burn are more likely to occur on days in spring and winter when the pollution effects of the burn can be more pronounced.
"To be clear, these would be days when the conditions for conducting a safe prescribed burn are met, but other atmospheric variables effectively increase air pollution stemming from the fire," says Johnson.
"It's important to note that, based on our survey, land managers in the Southeast already feel smoke management is a limiting factor for prescribed burns," says Garcia-Menendez. "In other words, they're not able to conduct these burns as often as they would like due to air quality concerns. Our study suggests that this challenge may only get worse.
"It's also important to note that the calculations in our study were made using an assumption that the area of land treated with prescribed burns would be approximately the same in 2055-2059 as it was in 2018," Garcia-Menendez says. "But we're now seeing a big push to increase the number of prescribed burns, largely in an attempt to reduce the underbrush that contributes to uncontrolled wildfires. If we do see an increase in prescribed burns, that will increase the air quality impacts.
"That doesn't mean those burns aren't necessary, but it is something we would have to address in terms of both public health and public policy."
The paper, "Impacts of Climate Change on Land Management and Wildland Fire Smoke in the Southeastern United States," is published open access in the journal Environmental Research Letters.
This research drew on work supported by the National Science Foundation under grant 1751601 and the Joint Fire Science Program under Project 21-1-01-18. The research was also supported by a U.S. Geological Survey Science to Action Fellowship.
