In the Line of Fire: Consequences of Human-Ignited Wildfires to Homes in the U.S. (1992–2015)

Abstract

With climate-driven increases in wildfires in the western U.S., it is imperative to understand how the risk to homes is also changing nationwide. Here, we quantify the number of homes threatened, suppression costs, and ignition sources for 1.6 million wildfires in the United States (U.S.; 1992–2015). Human-caused wildfires accounted for 97% of the residential homes threatened (within 1 km of a wildfire) and nearly a third of suppression costs. This study illustrates how the wildland-urban interface (WUI), which accounts for only a small portion of U.S. land area (~10%), acts as a major source of fires, almost exclusively human-started. Cumulatively (1992–2015), just over one million homes were within human-caused wildfire perimeters in the WUI, where communities are built within flammable vegetation. An additional 58.8 million homes were within one kilometer across the 24-year record. On an annual basis in the WUI (1999–2014), an average of 2.5 million homes (2.2–2.8 million, 95% confidence interval) were threatened by human-started wildfires (within the perimeter and up to 1-km away). The number of residential homes in the WUI grew by ~32 million from 1990–2015. The convergence of warmer, drier conditions and greater development into flammable landscapes is leaving many communities vulnerable to human-caused wildfires. Cumulatively, ~60 million homes were at high fire risk (1992–2015), meaning they were within historic wildfire perimeters or up to 1 km away. On average, 2.5 million homes were considered high fire risk each year. Our analysis explored the consequences and costs of wildfire ignitions along a gradient from urban to wildlands between 1992–2015. This study illustrates how the WUI, a small portion of U.S. land area that contains homes within flammable wildland vegetation, acts as a major source of wildfires, almost exclusively human-started. These areas are a high priority for policy and management efforts that aim to reduce human ignitions and promote resilience to future fires, particularly as the number of residential homes in the WUI grew by ~32 million across this record and are expected to continue to grow in coming years.

Record‐setting climate enabled the extraordinary 2020 fire season in the western United States

“…increased area burned throughout the 21st century (Bowman et al, 2020; Figure 1c). leading to more fire disasters (Mietkiewicz et al, 2020). In 2020, the majority of burned area in California and the Pacific Northwest was from human-related ignitions.…”

Three Lines of Defense for Wildfire Risk Management in Electric Power Grids: A Review

“…This matter can be modeled in the wildfire rate of spread. The wildfire rate of spread can be obtained by Thomas formulae [26] as: (1 ) ,…”

“…According to the U.S. Department of Energy, there have been more than 2.7 million customers without power along California's coast due to 2019 wildfires and subsequent grid blackouts, indicating the lack of adequate resilience for a 21st-century power grid infrastructure. Expansion of human development in fire-prone areas and corresponding potential for human ignitions lead to growing risk to communities and critical infrastructure [1,2]. The 2018 Camp Fire alone in Northern California-which was sparked by PG&E's electrical infrastructure-took at least 85 lives and led to several firefighter injuries, burned a total of 153,336 acres, destroyed more than 18,800 homes and structures, and made PG&E face a multibillion-dollar lawsuit as a result [3,4].…”

Exposure of the Canadian wildland–human interface and population to wildland fire, under current and future climate conditions

“…In particular, hardwood species and young stands (0-30 years) are associated with reduced fire ignition and fire spread in the boreal and temperate forests (Krawchuk et al 2006;Bernier et al 2016;Marchal et al 2017;Erni et al 2018). Humans also affect overall fire activity directly through ignitions (Stocks et al 2002;Hanes et al 2019;Mietkiewicz et al 2020), fire management (Martell et al 1984;Stocks and Simard 1993;Hirsch and Martell 1996;Magnussen and Taylor 2012), and fuel management (Mouillot and Field 2005;Gralewicz et al 2012;Parisien et al 2016;Boulanger et al 2017), as well as indirectly through land use alterations (Bowman et al 2011) and climate change (Flannigan et al 2009). Negative impacts due to wildland fires are expected to worsen throughout the 21st century, particularly in the boreal forest.…”