"The modern era of megafires is often defined based on wildfire size," say Jennifer Balch and colleagues in a new study, "but it should be defined based on how fast fires grow and their consequent societal impacts." Balch and colleagues report that wildfire growth rates in the U.S. have surged over 250% over the last 2 decades. Although these fast-moving infernos, or "fast fires" – those spreading more than 1,620 hectares in a day – account for only 2.7% of wildfire events from 2001 to 2020, researchers report that they are responsible for 89% of the total structures damaged or destroyed and more than half of the costs incurred to suppress them. The findings underscore the importance of understanding fast fires to improve wildfire risk assessments, firefighting strategies, and community preparedness. Some of the deadliest and most destructive wildfires in recent U.S. history, such as the 2021 Marshall Fire in Colorado and the 2023 Lahaina Fire in Hawaii, share a common trait – rapid growth within hours of ignition. These fast-moving fires present significant challenges as they often outpace evacuation efforts and overwhelm firefighting operations, resulting in greater loss of life, infrastructure damage, and suppression costs. Despite this, traditional fire risk models are based on the probability of occurrence, wildfire size, and burn intensity rather than how fast wildfires can grow and move.
According to Jennifer Balch and colleagues, the lack of comprehensive national data on fire growth rates (FGRs) has hindered an understanding modern wildfire behavior and their consequent impacts. Derived from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) Burned Area Product, Balch et al. developed a Fire Event Delineation (FIRED) parameter dataset. Using this dataset, the authors analyzed the daily growth rates of more than 60,000 fires from 2001 to 2020 across the contiguous U.S. By identifying the fastest-growing fires during this period, the authors discovered that nearly half of all areas experienced destructive fast fires. Comparing these events with data from the Historical Settlement Data Compilation of the US (HISDAC-US) and government records on fire event suppression efforts (ICS-209-PLUS), Balch et al. found that fast fires accounted for 78% of structures destroyed, 66% of fatalities, and 61% ($18.9 billion) of the total fire suppression costs due to fires in 2001 to 2020. Moreover, the findings reveal that average FGRs in the Western U.S. in 2020 have increased by 249% relative to averages in 2001, with California experiencing a 398% rise in peak daily growth rate, indicating a significant escalation in fire speed across the last 2 decades.
