Only Who Can Prevent Forest Fires? Causes of a Subset of Wildfires in California, 2010-2021

Wildfires are increasing in frequency and intensity across much of the world, including in the western United States. Developing effective, research-informed strategies to prevent and mitigate wildfires requires a comprehensive understanding of their ignition causes. This study examines the causes of wildfire ignitions in California between 2010 and 2021, focusing on areas managed by the California Department of Forestry and Fire Protection (CAL FIRE). CAL FIRE oversees fire prevention and suppression for nearly one-third of California's land area, much of which lies within the wildland-urban interface, where human infrastructure intersects with wildland vegetation and is highly vulnerable to wildfires. Using CAL FIRE's annual Wildfire Activity Statistics reports, we analyzed data on the number of fires and the acreage burned by ignition cause. During the study period, 43,055 wildfires burned over 5.27 million acres in CAL FIRE's jurisdiction, with significant variation in annual acreage burned by each ignition source. Notably, lightning was responsible for only 5% of fires but accounted for over one-quarter of the acreage burned, mainly due to the exceptional 2020 wildfire season. Electrical power caused 9.4% of fires, collectively burning 20.9% of the total acreage over the study period. As climate change continues to exacerbate wildfire conditions, catastrophic wildfires are likely to persist. Understanding ignition patterns is critical for designing targeted prevention strategies. Our findings suggest that mitigating electrical power-related ignitions may offer a particularly impactful approach to reducing wildfire risk compared to other ignition sources.