Mudslide risk presents double-edged sword for California wildfire victims as wettest month looms

LOS ANGELES — Ferocious Santa Ana winds combined with months of generally bone-dry weather created a deadly firestorm across the Los Angeles area last week – a pattern that will only threaten to repeat until soaking rains come to rinse the parched landscape.

While no such rain is in the current forecast, any rain would now present a double-edged sword for those whose neighborhoods were ravaged by flames in the form of an increased risk of mudslides.

"Just a short period of moderate rainfall on a burn scar can lead to flash floods and debris flows," the National Weather Service said. "Rainfall that is normally absorbed by vegetation can run off almost instantly. This causes creeks and drainage areas to flood much sooner during a storm, and with more water, than normal."

In addition, soils inside burn scars can contain significant amounts of mud, boulders and vegetation.

"The powerful force of rushing water, soil, and rock, both within the burned area and downstream, can destroy culverts, bridges, roadways, and structures, and can cause injury or death if care is not taken," the NWS said.

The U.S. Geological Survey added that water used in the firefight adds to the recipe for disaster. 

Heavy rain events following wildfires have led to devastating mudflows along burn scar areas.

"In 2017, I was at the Thomas Fire in Santa Barbara," said FOX News Senior Correspondent William La Jeunesse. "We got some rain and the mudslide was incredible. It took down houses. It flipped over cars. It was huge. So they’re warning everyone here they’re trying to keep those debris basins clear. Those debris basins quickly get clogged by the mud and other debris — when those (rains) hit, then you get the flooding."

While Los Angeles averages just over 12 inches of rainfall a year, February is usually the city's wettest month of the season. Last February was particularly wet, with more than 10 inches of rain falling at Los Angeles International Airport. However, it became dry in a hurry, with only 0.12 inches of rain in May and just 0.03 inches received in the half-plus year since June 1, leaving the area tinder dry.

Mudslides can even happen without the rain

Officials have warned that burned hillsides are in danger of giving way even without the rain.

A charred landscape with broken water mains and an influx of water from firefighting efforts have destabilized hillsides.

FOX 11 Los Angeles reported that a $2 million oceanfront home, which survived the Palisades Fire, was split into two by a landslide.

"A warning to all the residents, no matter where you live in (Los Angeles) County, if you have slopes behind your homes, or if you're located on top of a slope, these slopes have become fragile," Mark Pestrella, director of Los Angeles County Public Works, warned Thursday. "The soil that is supporting your home has all become fragile and damaged, due to the events that we've had … There are mud and debris flow hazards that are existing even when it's not raining. So we want people to be very careful."

The forecast for the next 10 days remains generally dry across Los Angeles with even a potentially worrying return of Santa Ana winds for next week. The monthly February outlook issued by NOAA’s Climate Prediction Center indicates equal chances of above- or below-normal precipitation for the Los Angeles area.