Impact of climate change and climate variability on fire season onset in California

Fire season onset in California based on fire weather has indicated an advancing trend, suggested to be driven by climate change. This, however, has not been assessed based on historical fire occurrence data. In this study, we assess the fire season onset for forested regions in California using fire occurrence records. We find that fire season onset has a significant relationship with the total burned area during the fire season, where an earlier onset is associated with a greater burned area. Using high-resolution climate data, we observe how antecedent temperature and precipitation modulate subsurface water buffers that determine the summer fuel aridity, and therefore the onset. With this mechanistic understanding, we assess the influence of precipitation and temperature variability, and climate change on the advancing trend of the historical onset. For Southern California domain, we find that precipitation variability has the greatest influence whereas climate change driven increase in temperature has the largest influence in Northern California.