Examining extreme single-day fire spread events
The Thomas Fire burns in the hills above Los Padres National Forest during a firing operation, December 20th, 2017. USDA Forest Service photo by Stuart Palley.
Recent wildfire activity is notable not only for its expansion in total area burned but also for its large, single-day fire spread events that challenge ecological systems and human communities. For example, 4 million hectares burned in the U.S. in the 2020 fire season. A team of scientists gained new insight into the relationships between extreme single-day fire spread events, annual area burned, and fire season climate — and predicted changes.
The scientists used a satellite-derived dataset of daily fire spread and gridded climate data to assess relationships between extreme single-day fire spread events, annual area burned, and fire season climate. They then developed models to predict the annual number of extreme fire spread events and annual area burned under a 2°C warming scenario.
The team found that extreme fire spread events, defined as burning more than 1100 hectares (2700 acres) in a single day, disproportionately impact cumulative area burned. They identified 441 extreme events in 2020 that together burned 2.2 million hectares across our study area, contrasting with an average of 168 per year that burned 0.5 million hectares annually between 2002 and 2019. Models predict that the annual number of extreme fire spread events will more than double under 2°C warming. Safeguarding human communities and supporting resilient ecosystems will require new lines of scientific inquiry, updated land management approaches, and accelerated climate mitigation efforts.
The top 10 percent of single-day fire spread events account for more than half (58 percent) of all area burned between 2002 and 2020, and just 1 percent of single-day events burned 20 percent of the total. Extreme fire spread events are linked to warmer and drier fire seasons. Under 2°C warming, the scientists predict that the number of extreme single-day events more than doubles compared to recent years, as does annual area burned. Fire years like 2020 will become more common and future extremes will surpass anything witnessed yet. Therefore, reducing exposure to future extremes calls for new land management approaches, increased attention to community preparedness, and climate mitigation.