California could be subject to a powerful series of storms, capable of costing $300 billion in damages — three times as much as a severe earthquake in the southern part of the state, according to a new report by the U.S. Geological Survey.
The “ARkStorm Scenario,” prepared by USGS and released at the ARkStorm Summit in Sacramento this week, combines pre-historical geologic flood history in California with modern flood mapping and climate-change projections to produce a hypothetical, but plausible scenario aimed at preparing the emergency response community for this type of hazard.
USGS said the hypothetical storm, also dubbed the “other Big One,” would strike the U.S. West Coast and be similar to the intense California winter storms of 1861 and 1862 that left the central valley of California impassible. The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years.
The report projects property damage from the storms to exceed $300 billion, mostly from flooding. Demand surge (an increase in labor rates and other repair costs after major natural disasters) could increase property losses by 20 percent. Agricultural losses and other costs to repair lifelines, dewater (drain) flooded islands, and repair damage from landslides, brings the total direct property loss to nearly $400 billion, of which $20 to $30 billion would be recoverable through public and commercial insurance.
The high costs are a result of flooding,which in many cases would overwhelm flood protection systems that are typically designed to resist 100- to 200-year runoffs. The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Wind speeds in some places reach 125 miles per hour, hurricane-force winds. Across wider areas of the state, winds reach 60 miles per hour. Hundreds of landslides damage roads, highways, and homes.
Power, water, sewer, and other lifelines experience damage that takes weeks or months to restore. Flooding evacuation could involve 1.5 million residents in the inland region and delta counties. Business interruption costs reach $325 billion in addition to the $400 property repair costs, meaning that an ARkStorm could cost on the order of $725 billion, which is nearly 3 times the loss deemed to be realistic by the ShakeOut authors for a magnitude7.8 earthquake on the San Andreas Fault in southern California, an event with roughly the same annual occurrence probability.
To download the full report, visit http://pubs.usgs.gov/of/2010/1312/
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