Heavy rains unleashed destructive rivers of mud and debris in Santa Barbara County, Southern California, early this week, sweeping homes from their foundations and stretching emergency services. At least 17 people were killed and dozens are unaccounted for.
The rains followed forest fires that burnt hundreds of thousands of hectares in the nearby Santa Ynez Mountains the month before, leaving the landscape dry and barren, and setting the scene for the tragedy. Pounding rain struck at around 2:30 AM Tuesday, January 9, causing a flash flood and sending mud and massive boulders rolling into residential neighborhoods.
“Although local residents said they had never seen anything like it, the disaster followed a typical pattern,” says Allianz Re expert Katie Wenigmann. “After wildfires, the vegetation is stripped away, and the scorched soil can change and become impervious to water. “Especially the first rainfall can bring tragedy, but the risk of debris flows can remain for years. Destructive landslides occur because the earth cannot absorb the water, so it runs off, and the land is easily eroded because no vegetation is holding it together. In California, the effect was exacerbated by the steep slopes of the nearby hills and mountains.”