Tens of thousands of people living in and around Southern California mountains scarred by deadly wildfire could face added dangers of mudslides (search) and flooding in the months to come, officials say.

"The risk is huge," said Peter Wohlgemuth, a hydrologist with the U.S. Forest Service (search). "If you get Noah's flood coming after these fires, a pile of sand bags isn't going to help much."

The firestorm that roared through the San Bernardino Mountains (search) burned away layers of vegetation -- twigs, leaves and moss -- leaving vast areas of top soil exposed.

As a result, the ground is more susceptible to erosion and will retain much less water when the rainy season arrives, sending sheets of storm runoff racing toward the valleys below.

"The vegetation is gone, and so there's nothing to hold the water back," said Thomas Meixner, assistant professor of hydrology and water resources at the University of California, Riverside. "It's a real hazard."

To guard against the potential of mudslides and flooding, authorities are working to identify and protect areas facing the greatest threat, said the San Bernardino National Forest Service's Steve Loe, who's helping coordinate a rehabilitation team to cope with the destruction.

Though few measures have been taken yet, there are ways to combat mudslides that include planting fast-growing grass, clearing water channels of excess debris and putting up structures to collect mud and rocks, officials said.

Foothill communities in Rancho Cucamonga, Devore and San Bernardino could be vulnerable, Loe said. In Simi Valley, Santa Clarita and other areas near hillsides also may need protection, authorities said. The potential for ash and debris flow also exists in San Diego County's Ramona and Alpine communities, among others, officials said.

On Friday, showers caused officials to issue a flash flood warning in parts of eastern Ventura County where the Piru Fire desiccated the soil. The warning was expected to be lifted later Friday night.

The mountains are expected to see about a half-inch of rain through Tuesday from two systems moving in from the west and the north, said Bill Hoffer, spokesman for the National Weather Service. Up to six inches of snowfall are forecast for elevations above 5,000 feet.

Experts said the mountainside, much of it charred bare by days of fires, can absorb the level of rainfall expected over the next several days. Of greater concern are the heavy winter storms that arrive in December and dump multiple inches, experts said.

"We've seen whole blocks of homes that were filled with mud 6 to 8 feet deep," Loe said. "That was from a fire smaller than this."