California Braces for Intense Rain and Floods as Some Evacuate in LA Fire Areas

Heavy rain fell across a large swath of Southern California on Thursday afternoon as the region braced for intense bouts of precipitation that began to flood roads and threatened to unleash debris flows in areas recently burned by wildfires.

The Southern California areas scorched by flames last month were of particular concern because the soil in those areas can repel water and allow sheets of mud to race downhill and collect debris along the way.

Just before 4 p.m., the National Weather Service issued flash flood warnings in Malibu and Pacific Palisades, two communities that suffered heavy damage during the Palisades fire last month. Shortly thereafter, the same warning was issued in the Altadena area, where thousands of structures were destroyed by the Eaton fire, and across much of Los Angeles County, affecting about seven million people.

The warnings mean that flooding has begun or is imminent in those areas. A torrent of rain within a short period could pose particular problems. Already, muddy water was cascading across parts of the Pacific Coast Highway, prompting officials to shut the roadway until at least Friday morning.

If heavy precipitation falls over the burn scars, “there will be the potential for very severe debris flows to occur in addition to mudslides and rock slides,” said Ariel Cohen, the meteorologist in charge of the National Weather Service that oversees the Los Angeles region.

“Everyone needs to be at a high state of readiness,” Dr. Cohen added.

More than 100 homes were under mandatory evacuation orders in the city of Los Angeles, Jim McDonnell, the Los Angeles police chief, said Thursday morning. The Palisades fire destroyed thousands of homes in the city’s Pacific Palisades neighborhood last month, and hillsides remain vulnerable in the area.

Elsewhere in Los Angeles County, evacuation warnings and orders were issued for areas recently affected by the Eaton fire, which burned more than 14,000 acres and destroyed more than 9,400 structures. On Thursday morning, some residents in Sierra Madre, Calif., were told to evacuate before the worst of the storm.

In nearby Altadena, water gushed downhill alongside the curb on Lake Avenue, which runs through the middle of the community, during the afternoon. Muddy water rushed down driveways and nearby neighborhood streets, carrying small pieces of charred debris with it.

Sheriff Robert Luna of Los Angeles County said at a news conference on Wednesday that officials had been notifying residents in areas with elevated risk, and he urged residents to heed to any evacuation orders they received.

“Storms can bring sudden and severe conditions that make staying back home extremely risky,” Sheriff Luna said. “Do not take that chance.”

Landslides could prevent law enforcement personnel and emergency crews from being able to reach those in need, Sheriff Luna added.

Concerns this week extended beyond areas affected by the Palisades and Eaton fires. Mark Pestrella, the director of the Los Angeles County Public Works Department, said on Wednesday that any burn scar area from a fire within the past year could be at risk.

In Orange County, the Sheriff’s Department issued an evacuation warning for the area near the site of the Airport fire, which burned more than 20,000 acres in the foothills of the Santa Ana Mountains. In San Bernardino County, the sheriff’s office also issued an evacuation order, citing the potential for mud and debris flow.

In Altadena, Makis Dasigenis, 69, said on Thursday afternoon that exhaustion from the firestorm and, now, the pounding rain was setting in among residents. Mr. Dasigenis, a retired banker, described how he fought to save his home during the Eaton fire using a water pump.

“All of us are dealing with insurance companies and trying to arrange for cleanup and this and that,” he said. “It’s been exhausting, and it will take months before it’s over.”

As stronger rain began to hit the neighborhood, Mr. Dasigenis said he wasn’t too worried about a mudslide or debris from the storm, which he felt would be more of a concern farther north from his home toward the San Gabriel Mountains.

The California Governor’s Office of Emergency Services said that, to prepare for the heavy rain, it had positioned resources across 14 counties, from Sonoma County in Northern California to San Diego County at the southern border.

Intense storms were also hitting the Bay Area and other parts of Northern California, but they were not expected to cause as many problems as in Southern California. On Thursday morning, the Santa Cruz County Sheriff’s Office issued an evacuation order for parts of the county because of rising creek levels; evacuation orders were lifted by the early afternoon.

In the Sierra Nevada, snow was heavy enough to force the closure of Interstate 80 because of low visibility and vehicles spinning out on icy road surfaces, according to Caltrans.

In Southern California, officials in Santa Barbara County, which experienced a deadly mudslide in 2018 along with flooding in recent years, have been preparing for the storm since late last week, said Jackie Ruiz, a spokeswoman for the county’s emergency management office.

“We had back-to-back years of pretty intense rain here,” Ms. Ruiz said, “so it’s something that we’re very familiar with in the community.”

On Wednesday, sheriff’s deputies were knocking on the doors of about 50 properties within the burn scar area of the Lake fire, which burned more than 38,000 acres last year, Ms. Ruiz said. Officials were also trying to reach people who live in encampments in creek beds, underpasses and other places that are prone to flooding, she said.

In San Luis Obispo County on the Central Coast, officials were preparing for possible flooding as severe as what occurred in January 2023, when heavy rainfall inundated communities. During that storm, a 5-year-old boy was swept away and killed when floodwaters overwhelmed his mother’s vehicle.

Jonathan Wolfe, Amy Graff and Amanda Holpuch contributed reporting.