Researchers quantify the trend toward increasing autumn wildfire danger in California

Autumn Days Fire weather index above 95th percentile
Fire Weather Index in California in September, October, and November since the 1980s. From the research paper.

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:

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.

NIFC releases prediction for wildfire potential, April through July

Wildfire potential weather July

Today there is a bit of good news for anyone worried about how firefighters will control wildfires during the current coronavirus pandemic. The wildfire potential outlook issued by the National Interagency Fire Center (NIFC) on March 1 predicted that the coastal areas of Central and Southern California would have above average conditions for April, but that changed in a new outlook released today. As you can see in the map above there are no areas in the United States with forecasts for above normal wildfire activity in April.

That is expected to change in May with enhanced potential in southeast Arizona and south Florida. Then in June portions of northeast California and the southern areas of Nevada and Utah will be added to the list. In July firefighters could be busy in Washington, Oregon, and northern California.

The outlook comes from the Predictive Services section at NIFC and represents the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit.

The temperature outlook from the National Weather Service for April through June predicts higher than average temperatures in the west, southwest, southeast, and east. Precipitation for the period should be normal, except drier in the northwest and more rain than normal in the east one-third of the country.

Below:

  • An excerpt from the NIFC narrative report for the next several months;
  • More of NIFC’s monthly graphical outlooks;
  • NOAA’s three-month temperature and precipitation forecasts;
  • Drought Monitor;
  • Keetch-Byram Drought Index.

“Mountain snowpack remained near to above average on the Continental Divide, along the Canadian Border, and across the Alaskan Interior. It was below average to well below average across the High Sierra, Southern Cascades, Great Basin, Sawtooth Mountains, Kenai Peninsula, and the Chugach Mountains. Snowpack melting rates will need to be monitored closely in these areas. Drought development and slight intensification was observed across California, Oregon, portions of the Great Basin, South Texas and Florida.

“Wildfire activity in April should continue to be light and focused in four areas. South Florida has been extremely dry. Fuels are receptive. Pregreenup activity may occur during warm and breezy periods along the Rocky Mountain Front as fronts pass. New Mexico begins to enter its season late in the month. In Alaska, hold over activity from the previous season can reemerge as the snowpack melts off. The potential for each in April 2020 is not expected exceed what is observed typically, except possibly in Florida.

“May is a transitional period. Fuels in southwestern areas dry, and fuels across northwestern areas enter peak greenup. The Southwest, California and Alaska begin to more fully enter fire season while other regions remain out of season. A normal transition into the Western fire season is expected. Areas of concern will be the middle elevations across much of California. In June and July, the West and Alaska enter their peak seasons. Activity across Oregon and Central through Northern California may be above normal. While overall Normal significant large fire potential is expected across most of the Southwest, some portions of the Great Basin and western portions of the Northern Rockies may experience elevated potential and activity as well. The Southwest and Alaska should transition out of fire season in July.”

Wildfire potential weather May Wildfire potential weather June Wildfire potential weather April

Temperature and precipitation outlook
Temperature and precipitation outlook for June through August, 2020.
Drought Monitor
Drought Monitor

KBDI