Human-related ignitions concurrent with high winds promote large wildfires across the USA

TitleHuman-related ignitions concurrent with high winds promote large wildfires across the USA
Publication TypeJournal Article
Year of Publication2018
AuthorsAbatzoglou, JT
Secondary AuthorsBalch, JK
Tertiary AuthorsBradley, BA
Subsidiary AuthorsKolden, CA
JournalInternational Journal of Wildland Fire
VolumeOnline early
Keywordsfire regimes, lightning, technical reports and journal articles, weather

Large wildfires (>40 ha) account for the majority of burned area across the contiguous United States (US) and appropriate substantial suppression resources. A variety of environmental and social factors influence wildfire growth and whether a fire overcomes initial attack efforts and becomes a large wildfire. However, little is known about how these factors differ between lightning-caused and human-caused wildfires. This study examines differences in temperature, vapour pressure deficit, fuel moisture and wind speed for large and small lightning- and human-caused wildfires during the initial days of fire activity at ecoregion scales across the US. Large fires of both human and lightning origin occurred coincident with above-normal temperature and vapour pressure deficit and below-normal 100-hour dead fuel moisture compared with small fires. Large human-caused wildfires occurred, on average, coincident with higher wind speeds than small human-caused wildfires and large lightning-caused wildfires. These results suggest the importance of winds in driving rapid fire growth that can allow fires to overcome many of the factors that typically inhibit large human-caused fires. Additionally, such findings highlight the interplay between human activity and meteorological conditions and the importance of incorporating winds in modelling large-fire risk in human-dominated landscapes.