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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.”
Debris and landslides are natural phenomena. One of the deadliest disasters on record was in the Vargas State on the northern coast of Venezuela in 1999. A series of mudslides were triggered by heavy rainfall that caused flash floods and claimed an estimated 30,000 lives – 10 percent of the region. Two towns, Carmen de Uria and Cerro Grande, were completely buried under mud.
Wenigmann, a civil engineer specialized in hydrology, says that while landslides are natural occurrences, human activity can be an underlying cause. Last August, nearly 500 people died on the outskirts of Freetown in Sierra Leone from mudslides. One cause was deforestation on the Sugar Loaf, one of the highest nearby mountains. The denuded red soil became saturated and cleaved off carrying trees and rocks before it in a path of destruction.
Authorities are aware of the danger of landslides. Californian officials, responding to warnings from the United States Geological Survey, issued mandatory evacuations for more than 6,000 people living in the area. Voluntary evacuation warnings were in effect for another 20,000 people. Only an estimated 15 percent of people in the mandatory evacuation area heeded the warning. Unfortunately, the mandatory evacuations did not include people downstream of the burnt area as officials did not expect the amount of rain that fell.
“When any extreme weather disaster occurs,” says Markus Stowasser, Head of Catastrophe Research and Development at Allianz Re, “climate change is one of the ‘usual suspects’ listed. It is, however, almost impossible to attribute any one event to climate change, but a clear pattern is emerging.” According to the National Centers for Environmental Information (NCEI), which has one of world’s largest archives of environmental data, 2017 was a year of “historic weather and climate disasters” in the United States. The country experienced 16 separate billion-dollar disasters. These included one drought, eight severe storms and Hurricane Harvey, which dropped an unprecedented amount of water on the Houston area, as well as Hurricane Irma and Maria. Between 1980 and 2017, the annual average of events was 5.8. In comparison, the average for the five most recent years (2013–2017) is 11.6 events.
“It makes sense that extreme precipitation events would be increasing in both frequency and intensity,” says Stowasser. “In a warmer world, there is more water in the atmosphere which can rain out and consequently lead to higher risk of flooding.”
A report from the Potsdam Institute for Climate Impact Research gives an insight into the scope of the challenge until the 2040s. If the impact of climate change cannot be reduced, the U.S. will need to at least double its protection level to avoid dramatic increases in river flood risks. Africa, India, Indonesia and Central Europe, including Germany, will also face severe flooding unless additional prevention measures are undertaken.
Stowasser says 2017 was a wakeup call. “The indications are that extreme weather events – especially flooding and all the tragedy that involves – will be more severe in the future unless we make dramatic reductions in greenhouses gas emissions to limit global warming.”
The Allianz Group is one of the world's leading insurers and asset managers with more than 86 million retail and corporate customers. Allianz customers benefit from a broad range of personal and corporate insurance services, ranging from property, life and health insurance to assistance services to credit insurance and global business insurance. Allianz is one of the world’s largest investors, managing over 650 billion euros on behalf of its insurance customers while our asset managers Allianz Global Investors and PIMCO manage an additional 1.4 trillion euros of third-party assets. Thanks to our systematic integration of ecological and social criteria in our business processes and investment decisions, we hold a leading position in the Dow Jones Sustainability Index. In 2016, over 140,000 employees in more than 70 countries achieved total revenues of 122 billion euros and an operating profit of 11 billion euros for the group.
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