Why LA is burning in the middle of winter

“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 high.

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 them forms clouds. This means by the time they hit the 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 mean the fires can rush downhill.

Mullins 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,” said Mullins, who is also a councillor with the Climate Council.

“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.”

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

Porter said the palm trees are an even bigger problem.

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

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

The Black Summer bushfires of 2023-24 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,” Mullins said.

With AP