Recent Increases in Large Wildfires and Corresponding Circulation Changes in California’s South Coast

Abstract:

California’s South Coast has experienced several extreme wildfires in recent decades. Besides the contribution of warming climate on inducing hotter and drier environments, wildfires in California’s South Coast are highly relevant to the meteorological system. We investigate wildfires in California’s South Coast and relative circulation changes since 1979. The average area burned by wildfire has typically doubled during May–September and increased fivefold during October–December over the last two decades. Vapor pressure deficits present an increasing trend statewide in California in summer, while during October–December, the vapor pressure deficit increases primarily in Southern California with increased variance in California’s South Coast. The circulations present more stable conditions in summer, resulting in heatwave anomalies. During October–December, increasing variance in upper-level jet streams associated with an equatorward extension of surface high-pressure anomalies induces substantial offshore wind events. These circulation changes combined with the effects of global warming increase the risk of massive wildfires in California’s South Coast.