The character and changing frequency of extreme California fire weather

These changes are likely not anthropogenically caused and the frequency of such events is projected to decrease under continuing climate change. However, significant future increases are found for WTs associated with thermal-low-pressure systems along the California coast and in the Sierra west region. These increases in southern California are mainly due to increasing greenhouse-gas forcing and arise from the larger ocean-land temperature gradient while aerosol forcing changes are driving most of the increased frequency in central and northern California due to a reduction of relative humidity over land and a strengthening of low-pressure anomalies over the coast.

These WT frequency changes could permit more weather favorable for large fire growth in summer and less in fall, further enhancing the risk of catastrophic fires due to hotter and drier summers in future climates.