Local and national news, NPR, things to do, food recommendations and guides to Los Angeles, Orange County and the Inland Empire
Stay Connected
Listen

Share This

Climate and Environment

Forecast for heaviest period of rain lasts until Monday afternoon. What we know about risks for mudslides

A home in a canyon is surrounded by mud and debris.
After the Thomas Fire, heavy rains triggered tremendous mud and debris flows in Montecito in early 2018. Rains following fires always raise concerns.
(
Al Seib
/
Los Angeles Times via Getty Images
)

Congress has cut federal funding for public media — a $3.4 million loss for LAist. We count on readers like you to protect our nonprofit newsroom. Become a monthly member and sustain local journalism.

With the arrival of much-needed rain finally, debris flows are a real concern below steep, recently burned areas. Just how much water, rock, mud and other debris can flow will depend on how much rain falls in a short period.

Where things stand

Rain is expected to stick around from Saturday through Monday, though the period of greatest risk will be between 4 p.m. Sunday and 4 p.m. Monday. That's when the heaviest precipitation is expected to fall, according to the National Weather Service.

While 0.25 inches an hour is likely across the broader region, isolated thunderstorms could drop more than 0.5 inches an hour, exceeding the threshold of concern for debris flows. Anticipate problems if rainfall rates exceed a quarter-inch in 15 minutes, especially in mountainous areas.

The NWS will issue additional flood watches as needed.

What we know about the risks

"I'm most worried about the Eaton Fire," said Jason Kean, research hydrologist with the U.S. Geological Survey.

That's because the steepness of the San Gabriel Mountains and the deep drainages that run throughout can capture tons of debris, funneling mud, plants and rocks toward communities below. There's a long history of mudslides in the area, which is why a network of debris basins was built.

While the overall risk should be quite low for this rain event, that doesn't mean we won't see isolated problems.

“The worst would be a debris flow that’s several feet deep, that closes roads in the area, isolates people in their homes and brings mud into homes,” said Ryan Kittell, meteorologist with the NWS.

If you live downhill from one of the burned areas and feel especially concerned, consider leaving ahead of the storm. If you choose not to leave, it would be a good idea to stock up with a few days' worth of food and water in case roads are blocked.

Post-fire debris flow risk is highest right after a wildfire, but lasts anywhere from three to five years after a blaze, depending on how much rain an area gets and how long it takes for plants to repopulate hillsides.

Not every fire gets a post-fire debris flow risk assessment. So far, the USGS has only received requests to perform debris flow modeling for the Eaton, Palisades and Hurst fires, according to Kean.

Palisades Fire

Map shows areas burned by the Palisades Fire
Palisades Fire perimeter and evacuation orders
(
CalFire
)

  • Acreage: 23,448 acres | Containment: 77%
  • Structures damaged or destroyed: 5,000 estimated destroyed, about 700 damaged | Deaths: 11
  • CalFire incident page

The Palisades Fire decimated significant sections of Pacific Palisades and Malibu.

Mudslide risk assessment:

Map shows likelihood of debris flow with darker areas the most likely.
Darker areas on the map are assessed as being most likely to see debris flow.
(
U.S. Geological Survey
)

Eaton Fire

A large fire perimeter is shown in shaded areas extending into neighborhoods.
Eaton Fire perimeter.
(
CalFire
)

  • Acreage: 14,021 | Containment: 95%
  • Structures damaged or destroyed: About 9,400 destroyed, more than 1,000 damaged | Deaths: 17
  • CalFire incident page

The Eaton Fire devastated whole neighborhoods of Altadena and forced mass evacuations from parts of Altadena, Pasadena, Sierra Madre and Glendale.

Mudslide risk assessment:

A debris flow map shows areas of most concern in darker shades.
Darker areas are assessed as being more likely to see debris flows.
(
Courtesy USGS
)

Hughes Fire

Perimeter of fire is shaded.
Hughes Fire perimeter as of Friday, Jan. 24.
(
CalFire
)

The Hughes Fire prompted the temporary shutdown of the 5 Freeway, evacuation orders and the shut down of many schools.

Mudslide risk assessment: The risk is still being assessed by the U.S. Geological Survey.

Hurst Fire

Perimeter of a fire is shaded and close to populated areas.
The Hurst Fire burn zone.
(
CalFire
)

The Hurst Fire started above Olive View Medical Center and spread toward the 210 Freeway in Sylmar.

Mudslide risk assessment:

Map shows likelihood of debris flow with darker areas the most likely.
Darker areas are assessed as being more likely to see debris flows.
(
U.S. Geological Survey
)

Kenneth Fire

An area in light gray shows the fire perimeter.
The area burned by the Kenneth Fire.
(
CalFire
)

The Kenneth Fire that broke out along the western edge of the San Fernando Valley and was fully contained relatively quickly. The fire started in the Upper Las Virgenes Canyon Open Space Preserve and pushed toward dense developments in the cities of Calabasas and Agoura.

Mudslide risk assessment: A USGS risk assessment wasn't performed for this fire.

Sunset Fire

Shaded gray area shows the perimeter of a fire that burned near densely populated areas.
Area burned by the Sunset Fire.
(
CalFire
)

The Sunset Fire forced evacuations of densely populated areas in the Hollywood Hills before being contained.

Mudslide risk assessment: A USGS risk assessment wasn't performed for this fire.

Other recent fires

Franklin Fire

  • Acreage: 4,037 acres | Containment: 100%
  • Structures damaged or destroyed: 28 damaged, 20 destroyed
  • CalFire incident page

The Franklin Fire sparked on Dec. 18 and was active for nine days.

Mudslide risk assessment:

Map shows likelihood of debris flow with darker areas the most likely.
Darker areas have been assessed as more likely to see debris flow.
(
U.S. Geological Survey
)

Auto Fire

This fire burned in a riverbed area in Ventura and was quickly contained.

Mudslide risk assessment: A USGS risk assessment wasn't performed for this fire.

Lidia Fire

This fire burned in a remote area north of Soledad Canyon Road in L.A. County.

Mudslide risk assessment: A USGS risk assessment wasn't performed for this fire.

Sepulveda Fire

The Woodley Fire was reported near North Woodley Avenue and the Sepulveda Basin. In the early hours of the fire, officials warned that it posed "a threat of crossing Burbank Boulevard."

Mudslide risk assessment: A USGS risk assessment wasn't performed for this fire.

Listen to our Big Burn podcast

Listen 39:42
Get ready now. Listen to our The Big Burn podcast
Jacob Margolis, LAist's science reporter, examines the new normal of big fires in California.

Do you have a question about the wildfires or fire recovery?
Check out LAist.com/FireFAQs to see if your question has already been answered. If not, submit your questions here, and we’ll do our best to get you an answer.

_

Fire resources and tips

Check out LAist's wildfire recovery guide

If you have to evacuate:

Navigating fire conditions:

How to help yourself and others:

How to start the recovery process:

What to do for your kids:

Prepare for the next disaster:

As Editor-in-Chief of our newsroom, I’m extremely proud of the work our top-notch journalists are doing here at LAist. We’re doing more hard-hitting watchdog journalism than ever before — powerful reporting on the economy, elections, climate and the homelessness crisis that is making a difference in your lives. At the same time, it’s never been more difficult to maintain a paywall-free, independent news source that informs, inspires, and engages everyone.

Simply put, we cannot do this essential work without your help. Federal funding for public media has been clawed back by Congress and that means LAist has lost $3.4 million in federal funding over the next two years. So we’re asking for your help. LAist has been there for you and we’re asking you to be here for us.

We rely on donations from readers like you to stay independent, which keeps our nonprofit newsroom strong and accountable to you.

No matter where you stand on the political spectrum, press freedom is at the core of keeping our nation free and fair. And as the landscape of free press changes, LAist will remain a voice you know and trust, but the amount of reader support we receive will help determine how strong of a newsroom we are going forward to cover the important news from our community.

Please take action today to support your trusted source for local news with a donation that makes sense for your budget.

Thank you for your generous support and believing in independent news.

Chip in now to fund your local journalism
A row of graphics payment types: Visa, MasterCard, Apple Pay and PayPal, and  below a lock with Secure Payment text to the right
(
LAist
)

Trending on LAist