Why California's mudslides are so devastating

(CNN)Southern Californians can't get a break from nature. First, wildfires scorched a massive area northwest of Los Angeles. Now catastrophic mudslides have swallowed homes and killed at least 15 people.

But a variety of unique factors have made this latest destruction especially calamitous.

Wildfires just torched the area

Last month the sprawling Thomas Fire destroyed more than 282,000 acres -- the equivalent of more than Dallas and Miami combined.
    That means vegetation that would normally be able to soak up floodwater no longer exists.
    "All these hills normally have a protective cover of chaparral," said Tom Fayram, Santa Barbara's deputy director of public works. "That's all gone. Almost 100% gone."
    Given the circumstances, it takes hardly any rain to produce a mudslide.
    "About a half an inch per hour can start to produce issues, mudslides," Robbie Monroe of the National Weather Service's Oxnard office told CNN.

    Its geology means rockslides, too

    In the foothills of Montecito, east of Santa Barbara, the soil just sits on rock -- "all rock," resident Dave Peterson said.
    "When that soil gets wet, it just slides off the rock," Peterson said. "It's a treacherous situation."
    Images of boulders crashing downhill proved Peterson's point.
    Mudslides pushed boulders near a broken fence in Carpinteria on Tuesday.

    The elevation drops off sharply

    "In these mountains, we go from 3,000 feet to sea level in sometimes just four or five miles," Fayram said.
    That means mudslides and rockslides happen quickly -- and with great intensity.
    Ben Hyatt of Montecito said his house was engulfed in a flash.
    "Mud came in an instant, like a dam breaking," he said. "(It) surrounded the house, 2 to 3 feet."

    Drought has exacerbated the problem

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    California has suffered from years of drought. Ironically, the rain currently deluging the area is actually needed to grow the vegetation that helps prevent mudslides.
    "We're kind of damned if we do and if we don't get rain," Fayram said. "We need the rain, but we don't need a serious debris-flow problem, either."
    Pamela Ueckert of Ventura said the disasters tormenting Southern California have been unbearable.
    "It's just too much to handle after everything that's happened," she said. "I just feel bad for people who lost their homes ... They shouldn't have to handle any more."