The ecological, societal, and economic cost of wildfire across the United States (U.S.) has increased in recent years. These increases have direct implications for forest managers, policy makers, and communities that live in and around fire-prone landscapes. More specifically, human communities are both at risk of wildfire danger and a primary cause of wildfire events across the U.S. For instance, human ignitions accounted for 81% (n = 698,415) of all wildfire ignitions in the U.S. between 2002-2013 and 96% of wildfire ignitions in the wildland-urban interface (WUI). To date, there has been no broad-scale analysis comparing wildfire characteristics and societal impacts among the WUI, very-low density housing (VLDH), and wildland areas across U.S. Thus, using a variety of satellite remotely sensed wildfire products and federal, state, and local records of wildfire ignitions on public and private lands, we quantified human influence on the wildfires across the U.S. among each of these three development classes. Additionally, we leveraged information contained in the U.S. Incident Situation Summary (ICS-209) reports to quantify total estimated fire suppression costs, total structures lost, and total lives lost from 2002-2013.
Between 2002-2013, human-caused wildfire accounted for >85% of burned areas within the WUI, whereas lightning ignitions accounted for >68% of burned areas in the wildlands . On average, >1,800 km2 of the WUI burns every year, with 96% of WUI fires started by people. Human ignitions in the WUI accounted for 48% (n = 333,073) of wildfires across the three development classes, but the WUI only represents 5% (14,302 km2) of total land area. Human-caused wildfire totaled 18% of all fire suppression costs ($2.5 billion), but 73% (n = 4557) of all the structures lost and 39% (n = 165) of all of the lives lost. The ICS-209 estimated costs for fire events in the three classes was over $13 billion (9241 fires). This equated to 1% of all the fires that occurred in the three classes from 2002-2013, accounting for >80% of the total spending budget for the entire U.S. (including Alaska and Hawaii). Humans are the major driver of wildfire ignitions across the U.S., especially within the WUI, where communities are already at the highest wildfire risk. Thus, reducing wildfire ignitions in the WUI and regions prone to human-started wildfires will reduce fire risk and associated societal disruption.