California wildfires fuelled by months of unusual extreme weather

Fast-moving wildfires in the Los Angeles area are burning out of control long after fire season normally ends in California. Powerful Santa Ana winds are not unusual for this time of year but they have arrived after months of drought. The combination has led to a disastrous series of fires, in a possible indication of how climate change is shifting the way fires behave in the state.

“While Santa Ana fires are nothing new in southern California, this type of explosive fire event has never happened in January before, and it’s only happened once in December,” says Crystal Kolden at the University of California, Merced.

As of 8 January, at least four wildfires were burning in the Los Angeles area, according to the California Department of Forestry and Fire Protection. The two largest fires are the Palisades fire and the Eaton fire, which have each burned more than 4000 hectares (10,000 acres) in a day. The fires have killed at least two people and destroyed at least a thousand homes, as well as forcing tens of thousands of people to evacuate. The fires have also threatened NASA’s Jet Propulsion Laboratory and the Getty Museum.

The strong Santa Ana winds have reached speeds of up to 129 kilometres (80 miles) per hour, fanning the flames and driving their rapid spread. The windstorm is expected to be the most intense one since 2011, with “extremely critical fire weather conditions” forecast to continue through the afternoon of 8 January, according to the US National Weather Service. Fire weather could continue as late as 10 January, challenging firefighting efforts.

This is the latest in a “very highly improbable sequence of extreme climate and weather events” that have contributed to the intense fires, says Park Williams at the University of California, Los Angeles (UCLA). The Santa Anas are a regular feature of southern California weather, but wet fall and winter weather usually limits their influence on fires. This year, that rainy weather still hasn’t arrived, leaving vegetation dried out and ready to burn. Plus, there is more vegetation as fuel thanks to a wet winter in 2023 that boosted growth. Intense heat and drought throughout 2024 dried it out.

The combination of lots of fine fuel, drought and strong, hot, dry winds makes for “the most explosive fire behaviour imaginable”, says Kolden.

Officials are still investigating what ignited the blazes. Understanding the role climate change may have played will also take some time. However, there is reason to think it has made the fires worse.

Above-average sea surface temperatures in the Pacific Ocean, probably driven in part by climate change, have also contributed to the dry conditions. According to Daniel Swain at UCLA, these higher ocean temperatures have created a ridge of high pressure that has blocked wet weather carried on the jet stream from reaching southern California.

The region has seen this kind of high-pressure weather system occur more frequently over the past fifty years, which may be a symptom of climate change, says Daniel Cayan at the University of California, San Diego.