Investigating spatiotemporal trends of large wildfires in California (1950–2020)

Abstract. A database capturing large wildfire perimeters (> 1,000 acres / 405 hectares; n=2,857) in the state of California in the United States was used to document trends in fire occurrence (as frequency of large wildfires per year) and fire severity (using total burned area as a proxy) per ecoregion for the study period 1950–2020. Approximately 20.67% of the total area of California has been burned by large wildfires during the study period; of this, approximately 8.01% of the total area of California has been burned repeatedly. Large wildfires are becoming more severe in the state of California, burning an average of 5,068 additional acres (2,051 additional hectares) of land each year, however large wildfires are not occurring more frequently across the entire state as originally postulated. Rather, certain ecoregions, particularly mountainous regions with coniferous forests, exhibit statistically significant increasing trends in both large wildfire severity and occurrence compared to other regions of the state, likely contributing to the sentiment that wildfires are becoming worse in the state overall. As conditions relating to climate change, extreme weather events, invasive species, population distribution, and fire management decisions continue to change, the impacts of larger, more frequent fires will likely be felt more broadly across the state of California.