The report, entitled "ARkStorm Scenario
", prepared by the U.S. Geological Survey, combines prehistoric 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.
The scenario describes a storm that could produce up to 10 feet of rain, cause extensive flooding (in many cases overwhelming the state’s flood-protection system) and result in more than $300 billion in damage. The scale of destruction in this storm scenario is four or five times the amount of damage that could be wrought by a major earthquake.
Although the report is hypothetical the storm scenario is not without precedent in California.
In an interview with the New York Times
, Marcia K. McNutt, the director of the geological survey, said that 150 years ago, during a storm that lasted 45 days in the winter of 1861-62, so much rain fell that a stretch of the Central Valley 300 miles long and 20 miles wide was flooded, from north of Sacramento south to Bakersfield, near the eastern desert.
According to USGS
the storms of 1861-62 turned "the Sacramento Valley into an inland sea, forcing the State Capital to be moved from Sacramento to San Francisco for a time, and requiring Governor Leland Stanford to take a rowboat to his inauguration. The storms wiped out nearly a third of the taxable land in California, leaving the State bankrupt."
Even larger storms than the one recorded in 1861 happened previously in California.
According to geological evidence huge super storms raged through the area in the years 212, 440, 603, 1029, 1418, and 1605.
The risk of such storms has been dormant for the last 150 years but a general warming period has prompted scientists to raise the risk level. Lucy Jones, chief scientist of the USGS Multi-Hazards Demonstration Project and architect of ARkStorm, said in a press release
, "We think this event happens once every 100 or 200 years or so, which puts it in the same category as our big San Andreas earthquakes. The ARkStorm is essentially two historic storms (January 1969 and February 1986) put back to back in a scientifically plausible way. The model is not an extremely extreme event."
Director Marcia McNutt says, "The time to begin taking action is now, before a devastating natural hazard event occurs."