Santa Ana winds: What is causing the deadly fires sweeping across Los Angeles?

Firefighters in Los Angeles County are battling five life-threatening wildfires 36 hours after the first flames broke out in the Palisades area, the California Department of Forestry and Fire Protection reports. The fires were whipped up in a flash thanks to a combination of unusually dry weather and hurricane-force gusts that reached speeds of up to 99 mph (160 km/h).

More than 100,000 LA residents have been evacuated from their homes and about 29,000 acres (11,300 hectares) have been burned by the five fires as of early Thursday morning (Jan. 9.) The fires have destroyed more than 1,000 structures so far and five confirmed fatalities have been reported, according to the Associated Press (AP).

The fires are flourishing due to dry conditions, while firefighters have reported that some hydrants in the Pacific Palisades are coming up dry, potentially hindering fire-extinguishing efforts, according to the Los Angeles Times. The blaze is expected to continue until Thursday, according to the National Weather Service (NWS.) Strong winds also grounded firefighting planes on Tuesday night, further hindering efforts to contain blazes, according to the LA Times.

The flames are being fanned by a dangerous windstorm, which could also threaten lives and cause damage to properties.

"A life-threatening, destructive, widespread windstorm is expected Tuesday afternoon through Wednesday morning," NWS said in a warning early on Jan. 8. "Please stay indoors and away from windows during this time, and expect power outages."

This windstorm is fueled in part by the powerful Santa Ana winds — dry and warm northeast winds that blow in from inner Southern California towards the coast.

What are the Santa Ana winds?

Santa Ana winds are created when large areas of high pressure become established over the Great Basin in the interior of western America, which includes much of Nevada and parts of Oregon, Idaho and Utah.

These dry desert winds move towards the southwest into California, where they descend over the Sierra mountains and dry out even more. As the air squeezes through mountain passes and canyons, it begins to flow faster, creating a powerful, rapid air flow by the time it hits the coast.

The extremely low humidity of these winds causes vegetation to dry out and become more susceptible to fire, with even the slightest spark capable of escalating into a large-scale blaze, stoked by the speeding winds.

According to NWS, sustained winds could reach up to 40 mph (65 km/h), with isolated speeds of up to 100 mph (160 km/h) in the mountains and foothills.

Five fires are currently raging: in the Pacific Palisades, Sylmar, Altadena/Pasadena, Acton and the Hollywood Hills. The Palisades fire has caused the most damage, burning through more than 17,000 acres (6,900 hectares) as of 04:39 a.m. EST, with the so-called Eaton fire, near Altadena Drive and Midwick Drive in Altadena and Pasadena, burning through 10,600 acres (4,300 hectares), according to the local fire department.

What do California smelt fish have to do with the fires?

The fires have also sparked backlash from president-elect Donald Trump, who claimed that California's water supply issues were a result of the state's water policies. In a post on his social networking site Truth Social on Jan. 8, Trump criticized California Governor Gavin Newsom for sacrificing the state's water supply in order to protect endangered smelt fish.

"Governor Gavin Newscum refused to sign the water restoration declaration put before him that would have allowed millions of gallons of water, from excess rain and snow melt from the North, to flow daily into many parts of California, including the areas that are currently burning in a virtually apocalyptic way," Trump wrote.

"He wanted to protect an essentially worthless fish called a smelt, by giving it less water (it didn't work!), but didn't care about the people of California. Now the ultimate price is being paid… He is the blame for this... A true disaster!"

However, Newsom's office refuted Trump's claim in a post on the social platform X: "There is no such document as the water restoration declaration — that is pure fiction," Governor Newsom's press office wrote. "The Governor is focused on protecting people, not playing politics, and making sure firefighters have all the resources they need."

Delta smelt (Hypomesus transpacificus) is a small fish that is only found in the Sacramento-San Joaquin estuary in California, according to the U.S. Environmental Protection Agency (EPA.) It is endangered in California. In efforts to conserve the species, federal and state regulations limit the amount of water that can be pumped from the Sacramento-San Joaquin river delta — water that Trump claimed would have helped tackle the wildfires, ABC News reports.

However, Mark Gold, water scarcity director for the Natural Resources Defence Council and a board member of the Metropolitan Water District of Southern California, said that Trump's comments did not accurately reflect the complex water supply systems across the state.

"Tying Bay-Delta management into devastating wildfires that have cost people's lives and homes is nothing short of irresponsible, and it's happening at a time when the Metropolitan Water District has the most water stored in its system in the history of the agency," he told local nonprofit news outlet CalMatters. "It's not a matter of having enough water coming from Northern California to put out a fire. It's about the continued devastating impacts of a changing climate."

The argument surrounding the Bay-Delta supply centers around water originating in rivers and snowmelt from Northern California. However, most of Los Angeles' water supply does not come from Northern California but rather a 112-year-old aqueduct that runs from the Owens Valley, east of the Sierra Nevada, as well as groundwater, according to CalMatters.

According to AP, the fire hydrants had most likely run dry because they were overstressed without the assistance from firefighting aircraft.

Editor's note: This article was updated at 11:00 a.m. ET on Jan.9 to include the latest developments and figures from the fires as well as details of the Delta smelt fish and its relevance to water management in California.