Quantifying fire-specific smoke severity

Rapidly changing wildfire regimes across the Western US has driven more frequent and severe wildfires, resulting in wide-ranging societal threats from the wildfires themselves and the smoke that they generate. However, common measures of fire severity focus on what is burned and do not account for the societal impacts of the smoke generated from each fire. We combine satellite-derived fire scars, air parcel trajectories from individual fires, and predicted smoke PM2.5 to link source fires to resulting smoke PM2.5 experienced by populations in the contiguous United States from April 2006-2020. We develop a new metric of fire-specific severity based on the cumulative population exposed to smoke PM2.5 over the duration of a fire. This measure is only weakly correlated with common measures of wildfire severity, including burned area, structures destroyed, and suppression cost. We find that while recent California fires contributed nearly half of the country's experienced smoke severity during our study period, the most severe individual fire was the 2007 Bugaboo fire in the Southeast. We estimate that a majority of experienced smoke PM2.5 comes from sources outside the local jurisdictions where the smoke is experienced, with 87% coming from fires in other counties and 60% from fires in other states. Our approach enables broad-scale assessment of whether specific fire characteristics affect smoke toxicity or impact, informs assessment of the cost-effectiveness of how suppression resources are allocated, and helps clarify the growing transboundary nature of local air quality.