Southern California Braces for Potential Mudslides as Rain Continues

A ferocious atmospheric river storm that has battered California for days began to taper off in Los Angeles on Tuesday, but officials warned that even small amounts of additional precipitation could set off landslides in rain-drenched Southern California.

Between Sunday and Tuesday morning, the storm dumped record-breaking amounts of rain on the Los Angeles basin and prompted millions of residents to stay home to avoid potential hazards. By Tuesday, Los Angeles officials had counted more than 380 mudslides and 35 damaged structures in the city, many situated in the hills above Hollywood and Beverly Hills. Seven of those buildings were deemed no longer safe to enter.

The atmospheric river had grown more intense south of Los Angeles by Tuesday morning and was dumping precipitation on Orange, San Diego and San Bernardino counties. The National Weather Service warned of the potential for flash floods in Anaheim, Newport Beach and Santa Ana.

In less than 48 hours, the storm has unleashed as much as a third of a year’s worth of annual rainfall in parts of Orange County, said Elizabeth Adams, a meteorologist with the National Weather Service office in San Diego. She said the rain wasn’t expected to let up until the weekend, with another storm system moving into the region on Wednesday.

“We’re just going to get a lot more rain over the next few days,” Ms. Adams said.

In Los Angeles, where the storm was weakening, showers were likely to continue through the evening, with the possibility of some occasional rain on Wednesday as well, said Ariel Cohen, a meteorologist with the National Weather Service in Los Angeles.

Mr. Cohen said the ground was extremely saturated after what he called one of the wettest storm systems to hit the greater Los Angeles area since record-keeping began. He cautioned Angelenos to stay vigilant on Tuesday, even if the skies seemed bluer.

“This is not a time to let our guard down,” Mr. Cohen said at a press briefing on Tuesday morning. “Because the soils are so saturated, supersaturated in fact — with six to 12 inches of rain across the region — it will take very little additional rain to cause landslides, mudslides, and other debris flows. Everyone needs to be at a high state of readiness.”

Across Southern California, dozens of people had to be plucked from floodwaters and the raging sea, including one man in Los Angeles County who leaped into the raging Los Angeles River to try to save his dog. In the Baldwin Hills neighborhood, an avalanche of mud smashed through a bedroom of a home.

But overall, the region has not suffered the worst-case flooding and other effects for which it had prepared, said Lindsey Horvath, a Los Angeles County supervisor.

“Instead, the damage has been more like 1,000 cuts — sinkholes, downed trees, areas of erosion,” she said at a news conference on Monday night.

Firefighters evacuated 16 people in the Studio City neighborhood on Monday after two homes on Lockridge Road sustained significant damage from debris that the storm had sent rushing through the area.

Residents walked the street almost in a daze on Monday morning, surveying the piles of mud and the jumble of rocks strewed across the road. Ankle-deep water gushed down a hill, carrying bits of debris along with it. Some residents of the tree-lined streets near Lockridge Road shoveled mud that had collected in their driveways, while city maintenance trucks passed back and forth, trying to clear the way.

In other parts of Los Angeles, residents ventured tentatively back into the world on Monday, splashing through intersections where water had pooled. Although officials urged people to stay off roads, nearly all campuses in the Los Angeles Unified School District remained open, and classes were expected to remain in session again on Tuesday.

In Northern California, residents were still recuperating from damage wrought by heavy winds that exceeded 90 miles per hour in some locations on Sunday. At one point, more than 850,000 businesses and homes were without power as winds downed power lines and damaged other electrical equipment, in what Pacific Gas & Electric, the state’s largest utility, said Sunday ranked among its top three outage days ever caused by storms.

The winds also turned deadly. A 41-year-old man in the Sacramento suburb of Carmichael, a 63-year-old woman in the Sacramento suburb of Fair Oaks and an 82-year-old man in Yuba City, north of Sacramento, were killed by falling trees in their backyards. In the Santa Cruz Mountains, a 45-year-old man died when a tree fell onto his home on Sunday. The four deaths so far have been the only fatalities from the storm.

During a news briefing on Monday evening, Mayor Karen Bass of Los Angeles stepped away to take a call from President Biden. When she returned to the podium, she held her cellphone next to the microphone with the president still on the other end. Mr. Biden, over speakerphone, called the city’s efforts “one hell of an operation” and said he had just gotten off the phone with Gov. Gavin Newsom.

“We’ll get any help on the way as soon as you guys request it,” Mr. Biden said. “So just let me know. That’s why I’m calling.”

Jill Cowan contributed reporting from Los Angeles.