Why LA is burning in the middle of winter

A lethal combination of drought and powerful desert winds has fuelled the catastrophic mid-winter fires in Los Angeles in what should be the city’s rainy season.

Flames were being pushed by Santa Ana winds topping 97km/h in some places and were expected to increase to 160km/h in mountains and foothills – including in areas that haven’t seen substantial rain in months.

Burning palm trees are like “Roman candles”, a veteran photographer says.Credit: AP

The Santa Ana winds were behind most of southern California’s worst wildfires in history. They topple powerlines, rapidly turn a spark into an inferno, and they can make fires run downhill.

Former Fire and Rescue NSW commissioner Greg Mullins, who has spent years studying and fighting fires alongside Californian firefighters, said: “I’ve fought fires during Santa Anas, and it’s scary because the fires run downhill just as fast as they do uphill.

“Those winds can be horrendous, and they are so dry that it does not matter if it is hot, you just get these incredible blast furnace fires.”

The Santa Ana winds are strong, gusty winds that bring hot, dry air from the desert to the Los Angeles basin. They are not unusual in autumn and winter, but they are usually far less intense.

They tend to coincide with the wettest season of the year. Los Angeles’ rainy season occurs from October to April, with most rain falling from December to February. This year, large parts of southern California, including most of Los Angeles, San Bernardino, Riverside, Orange and San Diego counties, are in drought. Los Angeles has not recorded rainfall over 2.54 millimetres – the threshold that would reduce wildfire risk – since last May.

Kent Porter, a photographer at The Press Democrat in Santa Rosa in northern California and who has been covering fires in the state for nearly 40 years, said the fire season had turned into an all-year phenomenon, especially in southern California. When he was in the Los Angeles area two weeks ago, he was shocked by how dry it was.

“They haven’t had any measurable precipitation since about July,” Porter said. “The drought is playing a big, big part in what is happening right now.”

The Santa Anas are caused by high pressure over the western deserts, and the sinking air becomes warmer and drier as it descends and flows towards southern California.

Between the desert and the Los Angeles basin are the San Bernardino Mountains, which top out at 3506 metres – far taller than Australia’s largest mountain, Kosciuszko, at 2228 metres.

The air is funnelled into mountain passes and canyons that separate the desert from the city, becoming faster like a river that suddenly narrows and turns into rapids.

Other air hits the mountain peaks, and what little moisture remains in it forms clouds. This means that by the time the winds hit coastal areas, they are totally dry and often rapidly warming.

Usually, Los Angeles has cooler, more humid breezes from the Pacific Ocean. A Santa Ana wind can plunge humidity to the single digits, causing vegetation, both living and dead, to dry out and become more flammable.

Fires usually travel from the valley to the ridgeline, but the pressure of the winds coming over the mountains means the fires can rush downhill.

Mullins, the former Fire and Rescue NSW commissioner, is also a councillor with the Climate Council. He said the winter fires were occurring in an environment very similar to the east coast of Australia, and the cause was clear.

“This is happening because of climate change, and it is what we predicted,” he said

“There is more energy in the environment because the atmosphere is hotter. Scientists will say they need to study the data, but I am saying this as a firefighter: this is unprecedented.”

Residents of a centre for seniors in Altadena are evacuated as the Los Angeles blaze approaches.Credit: AP

Mullins said the highly flammable dry coastal scrub burning around Los Angeles was similar to vegetation in parts of coastal Victoria.

Porter said palm trees were an even bigger problem.

“Palm trees are like big Roman candles … they’re 40 to 50 feet [12 to 15 metres] tall, they catch on fire, the palm fronds fly everywhere and [cast embers], and it just lights everything on fire,” he said.

The extending fire season is also a problem in Australia: climate change is closing the window of opportunity to carry out hazard-reduction burning, because dangerous conditions start earlier in the year.

The bushfires of 2019–20 on the Australian east coast actually started in late winter, though they did not become catastrophic until November.

The advent of winter fires on the US West Coast could have a material impact on firefighting in Australia because agencies in the two nations share resources, Mullins said.

“There will be heavy aircraft they need to fight those fires that they do not have access to because they are in Australia,” he said.

With AP

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