Roles of Synoptic Forcing on Observed Trends in California Wildfires

California’s wildfire frequency and severity with respect to the area burned have increased over recent years. This study investigates the impact of synoptic-scale forcing mechanisms on the increased frequency and severity of the observed California (CA) wildfires. Using wildfire and ECMWF ERA-5 reanalysis data, we analyze meteorological parameters for a composite of days in which wildfires that burn 1000 acres and more occur and further observe their differences from the June - August climatology for a period of 31 years (1991-2021). Our results show that high temperature and strong pressure gradient build-up precede fire initiation. High pressure is observed to push in over the north/northeast of CA and enhance localized dryness over the region. Furthermore, 500 hPa ridge is seen dominating parts of northern and southern CA several days before fire initiation, with an increasing frequency and area burned in the region. This is proven by the large-scale weather patterns, which play a significant role in driving wildfire activities. This finding is consistent with previous studies and thus critical in simulating fire-weather conditions. The current climatological study will be extended to investigate the future prevalence or reduction of fire events using results from regional or global circulation Models.