Temporal Patterns in Anthropogenic Wildfire Ignition

Because the majority of California wildfires are started by humans, it is logical that patterns of ignition should be related to social, as well as ecological factors. We explored the relationship between wildfire ignition and days of the week, hypothesizing that humans would cause disproportionately more ignitions on Saturdays and Sundays than on weekdays, because more people enter wildland areas and the wildland-urban interface on weekends.

We analyzed data from California’s Fire and Resource Assessment Program (FRAP) database, examining more than 8500 human-caused fires that occurred 1950-2009.

Overall, 15.5% of the fires began on Saturdays, and 16.4% on Sundays, compared to the 14.3% per day that would constitute an even distribution through the week. However, those numbers do obscure some other patterns that are evident in examination of varied time periods, fire causes, and administrative units. Weekend ignitions were most important in 1950s, and declined in importance through most of the 20th Century. Weekend ignitions were most overrepresented in wildfires with “campfire” as cause, and were actually disproportionately low for fires started by “equipment,” patterns that make sense in terms of recreational versus work-related human activities. Also logical was were the particularly high rates of weekend ignitions (19.4% Saturdays, 16.7% Sundays) in State Parks, reflecting their high weekend visitorship.

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