Projected smoke impacts from increased prescribed fire activity in California's high wildfire risk landscape

Abstract

California has experienced multiple catastrophic wildfires over the last decade, fostering the need for increased forest management and understanding of the health impacts of wildfire and prescribed fire smoke. We calculated air quality impacts from past wildfires and prescribed fires and estimated how air quality may be affected under a future scenario in which prescribed fire is proposed to more than double. We merged satellite and agency records to establish a 10-year (2008–2017) baseline wildfire and prescribed fire inventory for California. Daily emissions and dispersion modeling were used to evaluate relative contributions from wildfire and prescribed fire. We scaled up prescribed burns to reach the >200,000 ha per year target, modeled over eight cycles (years) to encompass 1.6 million hectare of California Department of Forestry and Fire Prevention Priority Landscapes 4&5. We found that baseline wildfire contributes up to 20x more smoke PM2.5 concentrations than baseline prescribed fire. Target prescribed fire scenario smoke concentrations are anticipated to be ∼3x that of baseline prescribed fire. Baseline and target prescribed fire scenarios do not contribute sufficient PM2.5 to exceed air quality standards from smoke alone at the community (ZIP code) level. Baseline wildfires contribute enough PM2.5 to cause unhealthy air quality, even without contributions from ambient background PM2.5. The target prescribed fire scenario only exceeds the baseline smoke from wildfire and prescribed fire in 4% of California ZIP codes. Overall, we found that air quality is impacted significantly more from wildfires than prescribed fires, past and proposed, for the majority of California.