SACRAMENTO -- California faces the risk not just of devastating earthquakes but also of a catastrophic storm that could tear at the coasts, inundate the Central Valley and cause four to five times as much economic damage as a large quake, scientists and emergency planners warn.
The potential for such a storm was described at a conference of federal and California officials that ended Friday. Combining advanced flood mapping and atmospheric projections with data on California's geologic flood history, more than 100 scientists calculated the probable consequences of a "superstorm" carrying tropical moisture from the South Pacific and dropping up to 10 feet of rain across the state.
"Floods are as much a part of our lives in California as earthquakes are," said Lucy Jones, the chief scientist for the U.S. Geological Survey's multi-hazards initiative, adding, "We are probably not going to be able to handle the biggest ones."
The geological survey estimates that such a storm could cause up to $300 billion in damage. The scientists' models estimate that almost one-fourth of the houses in California could experience some flood damage from one.
The conference was convened by the geological survey, the Federal Emergency Management Agency and the California Emergency Management Agency to help disaster-response planners draft new strategies to limit the storms' impact.
Climate scientists have for years noted that the rising temperature of the earth's atmosphere increases the amount of energy it stores, making more violent and extreme weather events more likely.
Californians have learned to expect earthquakes, such as the recent 4.1-magnitude temblor that struck south of San Jose, the way Floridians expect hurricanes.
The existing engineering systems that dispose of floodwater are so efficient that the effects of moderate storms often go unnoticed, Jones said. So while many Californians know whether they live or work close to an earthquake-prone fault and what to do should there be a serious quake, few realize that the state could be hit by storms that at their worst could rival the largest hurricanes that devastate the Gulf Coast and the southeastern Atlantic Seaboard.
Yet vast floods have also been documented, both through tree-ring data and more modern historical records. Marcia K. McNutt, the director of the geological survey, said that 150 years ago, over a few weeks in the winter of 1861-62, enough rain fell to inundate a stretch of the Central Valley 300 miles long and 20 miles wide, from north of Sacramento south to Bakersfield, near the eastern desert.
The storms lasted 45 days, creating lakes in parts of the Mojave Desert and, according to a survey account, "turning the Sacramento Valley into an inland sea, forcing the state capital to be moved from Sacramento to San Francisco for a time, and requiring Gov. Leland Stanford to take a rowboat to his inauguration."
Just like a major earthquake, a superstorm could be a severe blow to the state's agriculture and to the water-supply system that now diverts water from the north to Southern California.
Jones said in an interview that improved satellite imagery available in recent years allowed scientists to clearly identify what they call "atmospheric rivers" -- moisture-filled air currents up to 200 miles wide and 2,000 miles long, which flow from tropical regions of the Pacific Ocean to the West Coast.
The West Coast winter weather systems popularly known as the Pineapple Express, air currents carrying moisture from the Hawaiian Islandsare just one moderate subset of these rivers, Jones said. The abbreviation for atmospheric river, A.R., gave the geological survey the root of its name for these major weather events, which they call ARk storms.