Meteorological Environments Associated With California Wildfires and Their Potential Roles in Wildfire Changes During 1984-2017

California has experienced more wildfires in recent years, resulting in huge economic losses and threatening human health. Clarifying the meteorological environments of wildfires is foundational to improving the understanding and prediction of wildfires and their impacts. Here, 1,535 California wildfires during 1984-2017 are systematically investigated. Based on two key meteorological factors- temperature and moisture anomalies-all wildfires are classified into four groups: hot-dry, hot-wet, cold-dry, cold-wet. Most (similar to 60%) wildfires occurred on hot-dry days. Compositing the meteorological environments of the four groups shows that persistent high pressure and strong northeasterly wind descending from inland favor hot-dry conditions for wildfires. Self-organizing map analysis lends confidence in the large-scale meteorological pattern dominating hot-dry wildfires in California. Meteorological anomalies also influence wildfire size through their magnitudes, with moisture anomaly explaining the largest fraction (similar to 69%) of variability in wildfire sizes. In addition, 12.2% of wildfires occurred on hot-wet days, which may be related with lightning flashes. More lightning tends to trigger wildfires, but the wet condition helps to suppress the wildfire sizes. Total burned area by wildfires has significantly increased by similar to 3.6% per year, indicating a doubling of burned area in 2017 relative to 1984, mainly dominated by hot-dry wildfires in summer. Drying and warming in conjunction with strengthening of the high pressure in summer and fall have the potential to support more frequent and larger hot-dry wildfires in California during the past several decades.

Automated summary

The study investigates 1,535 California wildfires from 1984 to 2017, classifying them into four groups based on temperature and moisture anomalies. Most wildfires occurred on hot-dry days, with the meteorological anomalies influencing wildfire size as well.Overall, the total burned area by wildfires in California has significantly increased by 3.6% per year, mainly dominated by hot-dry wildfires in summer.