Researchers have quantified some of the factors that have led to an increase in southern California large wildfires during the autumn months in recent decades.
Here are examples of late season fires that occurred in southern California in 2017 and 2018:
- North Bay fires, October 2017
- Thomas Fire, December, 2017
- Camp Fire, November, 2018
- Woolsey Fire, November, 2018
The study defines autumn as September through November.
But their analysis goes much farther back than just three years. Among other things, they found that rising temperatures, declining snowpack, and decreasing precipitation in autumn and spring have acted to extend California’s fire season in the shoulder seasons. They also determined that climate change has already doubled the frequency of extreme fire weather days since the 1980s (see the illustration at the top of the article).
The research also found a long-term trend toward more extreme fire weather conditions occurring in both southern and northern California at the same time.
The study was conducted by Michael Goss, Daniel L. Swain, John T. Abatzoglou, Ali Sarhadi, Crystal Kolden, A. Park Williams, and Noah S. Diffenbaugh.