Evolving Fire Frequency in the Western United States and Its Links to Human Influence

Abstract Burned area and wildfire damages in the western United States (WUS) have increased dramatically in recent decades. Wildfire frequency, however, has shown trends that vary by data set, region, and fire size. Using a comprehensive fire occurrence data set screened for reporting artifacts from 1992 to 2020, we show a significant downward trend in annual fire frequency in WUS, with a significant contribution from decreasing human ignitions. Human‐caused fires significantly declined in California and Arizona, but increased in Wyoming. The relationship between human‐caused fires and population suggests a pyric transition, where fire frequency correlates positively to population in areas with very low population such as Wyoming and negatively where population is denser, such as in California and Arizona. Understanding the human influence on fire frequency trends beyond anthropogenic warming has strong implications for future projections of wildfire activity.