Why Los Angeles is burning: Origins of devastating wildfires explained

© Sippakorn Yamkasikorn/Pexels

The toll of the fires ravaging the Los Angeles metropolitan area and Southern California is catastrophic: 25 dead and more than 12,000 homes destroyedby the passage of these extreme fires. The first flames were spotted on January 7 by hikers in Joshua Tree National Park, and the state has been unabated ever since.

The blazes have grown, and as the flames continue to spread, authorities have ordered the evacuation of 88,000 residents, while another 84,000 remain on alert, according to Sheriff Robert Luna.

The role of high-altitude winds

High in the Sierra Nevada and White Mountains, at 1,200 meters above sea level, an invisible but devastating spectacle is playing out. The cold, denser air plunges toward the coastal areas like an aerial torrent. Alexander Gershunov, a meteorologist at the Scripps Institution of Oceanography in San Francisco, describes this phenomenon, dubbed Santa Ana Winds: “These downdrafts act like water in a blocked stream—they pool against the terrain, then accelerate into aerial cascades as they clear the ridges ».

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The result: Air humidity is reduced, flames are constantly fanned, and these violent air currents throw embers long distances, starting new fires quickly. Isolated gusts reached 100 mph in the Santa Monica Mountains last week. For January 15 and 16, the National Weather Service is maintaining “red flag” warnings. from central California to the Mexican border, anticipating particularly critical conditions until today.

In all, five major fires have been identified: the largest, the Palisades Fire (east of Malibu), the Eaton Fire (near the city of Altadena), the Kenneth Fire (towards Calabasas) and the Auto Fire (Ventura County). Joe Biden has called them the “most devastating » in California history.

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The Los Angeles metropolitan area is engulfed in flames. © California Governor’s Office of Emergency Services, NASA (FIRMS), California Department of Technology GIS, The New York Times, The Washington Post, The Los Angeles Times

The fatal equation: historic drought and atmospheric turbulence

The winter of 2024-2025 marked an all-time record for the City of Angels: the longest period without winter precipitation in 150 years; the drought is therefore extreme. The Los Angeles region, which usually experiences five Santa Ana episodes in December and four to five in January, finds itself this year in an unprecedented situation where these winds occur without the usual counterbalance of winter rains. One of the perverse effects of global warming.

The current atmospheric configuration presents an additional anomaly: the jet stream makes an unusual loop in the upper troposphere, pointing directly towards the Los Angeles basin. This disturbance amplifies the effect of the downdraft winds, transforming each patch of vegetation into a potential accelerator of the flames.

Faced with this confluence of extreme climatic events, only the absence of storms offers a small respite by avoiding the risk of ignitions by lightning. The massive mobilization of emergency services continues, while the Californian metropolis anxiously awaits the first saving rains of the winter.

Investigations into the origin of the first fires are currently continuing. The preferred hypothesis, for the moment, seems to be fireworks that were set off to celebrate the New Year. The strong winds are said to have restarted a slow combustion that had persisted for six days. This explanation is put forward by specialists, but the American authorities have not yet confirmed this theory. The Santa Ana winds show no signs of abating, which could unfortunately further increase the human and material toll.

• The fires in California have caused 25 deaths, destroyed more than 12,000 homes, and prompted the mass evacuation of tens of thousands of people.
• Strong, dry winds, combined with record drought, are fueling the rapid spread of flames on multiple fronts.
• The fires are likely to be caused by human activity, while extreme weather conditions continue to complicate relief efforts.

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