This story originally appeared on High Country News and is part of the Climate office collaboration.
In Southern California, wildfires in December are somewhat rare, but not entirely out of the norm. And this year, extremely dry conditions and strong Santa Ana winds have created the perfect recipe for dangerous late-year fires.
On the night of December 9, the Franklin Fire unleashed in the hills above Malibu, heartbreakingh approximately 3,000 acres in just 24 hours. As of noon on December 12, the fire was less than 10 percent contained, burning just over 4,000 acres and destroying at least seven structures.
Last month, the mountain fire ignited under similar conditions in neighboring Ventura County, reaching 1,000 acres in the first hour. In two days there were over 20,000 acres; 240 structures were destroyed before firefighters contained them in early December.
And it still hasn't rained, neither since the mountain fire nor throughout the fall.
It's true that Santa Ana winds – dry winds that blow from the high desert to the coast and bring low humidity, sometimes less than 10% – arise regularly in fall and winter. But what is less normal is the lack of precipitation gripping Southern California at present, although the region is not technically in a situation drought Again.
A weather station in downtown Los Angeles has recorded only 5.7 inches of rain this year, and not even a quarter of an inch fell in December, which is usually the middle of the rainy season in the region. Most years would have seen three or more days of rain around this time, enough to reduce some wildfire risks; about 90 percent of the region's precipitation come between October and the end of April.
“We are still waiting for the rainy season to begin in this part of the state, which would significantly wet fuels and remove the threat of major fires,” said John Abatzoglouprofessor of climatology at the University of California, Merced.
In wetter years, the windy season presents a lower fire risk. But today, “when the flames and the wind collide,” as Abatzoglou says, the landscape is ready to catch fire. Dry grass and shrubs are ready to burn, and the fire risk predicted by the Los Angeles County Fire Department on December 11, the day the fire grew significantly, was high or very high throughout the Los Angeles Basin, Santa Monica Mountains and Valley Santa Clarita. “It hasn’t rained yet this season in Southern California,” said Daniel Swainclimatologist at UCLA. “That’s the key. This is the real kicker.
High winds coinciding with parched vegetation aren't just a problem for Southern California. Dry conditions increase the risk of wildfires across the country – during the period East Coastthe spring and fall fire seasons, for example. And winter fires broke out elsewhere in the West: Colorado's rapid evolution Marshall Fire erupted on December 30, 2021, growing from a small grass fire to a suburban conflagration – which ultimately burned more than 1,000 homes – in just one hour.
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