Areas burned by Woolsey Fire now face possibility of mudslides

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Residents of Malibu and other areas devastated by the Woolsey Fire have a new threat to worry about this week, as rains approach coastal California.

Los Angeles County public officials are warning residents who live in areas prone to mudslides and debris flows—and burned areas in particular—to prepare for possible flooding this week.

A storm is expected to roll through Ventura and Santa Barbara counties on Wednesday and could soak parts of Los Angeles County, including the Santa Monica Mountains, where the Woolsey Fire has burned tens of thousands of acres of vegetation.

Rain will likely be “significant enough to cause some issues in and around the recent burn areas… with mud slides and rock slides possible,” says a forecast from the National Weather Service.

Flooding is more likely after fires, when burnt debris collects on hillsides and prevents the soil from absorbing the rainfall.

The Los Angeles Fire Department asked residents Tuesday to prepare for the rain by obtaining sandbags and being ready to shut off utilities if necessary. A statement from county officials urges residents not to take evacuation orders “lightly,” should they be made.

The good news is that, at this point, the weather service predicts that there’s only a 10 percent chance that rainfall this week in the burn areas will meet USGS thresholds for a debris flow hazard. To hit those thresholds, rainfall in burn areas would have to total half an inch in one hour—or .2 inches in 15 minutes.

“I don’t think we’ll see significant debris flows,” says weather service meteorologist Mike Wofford, adding that precipitation in this storm isn’t likely to be strong enough to dislodge detritus left behind by the fires.

The weather service predicts an 80 percent chance of rain in Malibu, Topanga, and Agoura Hills Wednesday night. Between .3 and .6 inches are expected throughout Los Angeles and Ventura counties, though the Santa Monica Mountains could get up to an inch of rain.

County officials have put together a website where those who may be affected by the approaching rain can get updated forecasts and information about emergency preparation.

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