CALIFORNIA:

200-year flood more devastating than major quake -- USGS

A massive California rain event -- one expected to occur once every 200 years -- would far surpass destruction caused by a "Big One" earthquake, causing more than $700 billion in damage and hobbling the state's economy for decades, federal scientists are warning.

U.S. Geological Survey scientists ran an extreme hypothetical, called "ARkStorm," through simulation models and determined that a deluge not seen in California since 1862 could potentially cause three times more damage than a large earthquake on the San Andreas Fault.

The 1861-62 winter storm -- what scientists call an "atmospheric river storm" -- lasted for 45 days, producing precipitation that exceeded what some areas would experience once every 500 to 1,000 years. The flooding was so bad it reduced taxable land by a third, bankrupted the state government and left parts of the Central Valley looking more like an inland sea than the fertile farming area that today forms the backbone of the state's economy.

So USGS ran a scenario based on two recent storms, in 1969 and 1986, acting as if the accumulation of both occurred back to back. They found that rain would fall several feet deep, flood 9 million homes and probably overwhelm thousands of miles of levees and reservoirs.

USGS Director Marcia McNutt called the scenario "hypothetical but very plausible" given California's historical rainfall trends as well as the predicted effects of climate change, which some say could heighten the likelihood of widespread flooding. The point of the study, she said, is to help emergency planning efforts, as one dollar spent pre-emptively avoids hundreds spent later, she said.

"If we had a catastrophic disaster that takes down the California economy, that is a problem of national significance," McNutt said.

Lucy Jones, the primary architect of the ARkStorm test at USGS, added that the strength of such a storm is comparable to a intense hurricane but could leave behind far more damage as the atmospheric river keeps dumping water after a longer period. She noted that California is the only state outside of the hurricane-prone Southeast that tends to see rainfall as large as, say, 16 inches over a three-day period.

"This has to happen at some point," Jones said. "How prepared are we? That's essentially unanswerable. No flood control system can be or should be built to withstand every possible storm."

'Serious questions'

ARkStorm report in hand, USGS held a conference last week with the Federal Emergency Management Agency and the California Emergency Management Agency to sound the alarm and try to get parties thinking about what comes next.

Participants included more than 100 academics who participated in the process over the last two years, including researchers from the physical sciences as well as economists and social scientists.

The study itself looks at prehistoric geologic flood history in California alongside climate projections and flood mapping to try and point to the areas most likely to get hit hardest. Most of the damage would come from flooding, with as much as one-fourth of all houses in California damaged on some level.

The report notes an initial $300 billion estimate in damage would likely be exceeded as serious flooding hampers the Central Valley, Orange County, Los Angeles County, San Diego, the San Francisco Bay area and other coastal communities. The report says:

  • Demand surge (an increase in labor rates and other repair costs) could increase property losses by 20 percent.
  • Agricultural losses and other costs to repair lifelines, drain flooded islands and repair damage from landslides, brings the total direct property loss to nearly $400 billion, of which $20 billion to $30 billion would be recoverable through insurance.
  • 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, and business interruption costs could reach $325 billion in addition to the $400 billion in property repair costs, bringing ARkStorm's pricetag to the neighborhood of $725 billion.

"An ARkStorm raises serious questions about the ability of existing federal, state and local disaster planning to handle a disaster of this magnitude," the report concludes.

Also detailed in the report are the first-ever landslide susceptibility maps for California, with hotspots identified along active coastal ranges, which have long been highly vulnerable to fatal slides in the middle of population centers. Environmental damage was also assessed, given the likelihood that a series of storms akin to 1861-62 would overwhelm wastewater treatment facilities, refineries, mining operations and other industrial sources.

Jones said the report, which did not look at effects on marine life, would at the very least bring severe runoff from industrial sources that would be carried into urban areas in a swirling mix.

"It's not something we usually talk about before lunch," she said. "It's an appalling mix."

Establishing a warning system

The conclusion for emergency planners is that such a scenario, many times worse than a Hurricane Katrina, would likely involve "decades of recovery" rather than months or years, said Nancy Ward of FEMA.

So the ARkStorm project reached out to emergency planners, businesses, universities, government agencies and others who prepare for major natural disasters, much like the "ShakeOut" earthquake scenario, published in May 2008 by USGS, looked at the effects of a 7.8 earthquake on the San Andreas Fault in Southern California.

"This is not just a 72-hour response, this is not just months of recovery," Ward said of the ARkStorm scenario.

While comparisons to earthquake planning are inevitable in California, the experts said the type of rainfall assessed in the report would trump the biggest of quakes, including the 1906 trembler in San Francisco that burned much of the city to the ground and killed more than 3,000 residents.

Mark Jackson, of the National Weather Service, noted that an 1861-level rain event would be felt up and down the state, while a repeat of the 1906 quake -- which measured about 8 on the Richter scale and ruptured 296 miles of the San Andreas Fault -- would be more localized, even if devastating.

ARkStorm, he said, "is not just what happens in your backyard. It would have a domino effect all the way through."

Jackson is currently engaged in trying to set up a warning system similar to the categories widely invoked to describe hurricane intensity. The floods in Southern California in December, for instance, measured about 20 "Mississippi atmospheric rivers" (about a Category 2 or 3 storm), while ARkStorm would easily surpass 50 Mississippis, he explained, comparing the amount of likely rainfall to the length and width of several Mississippi rivers.

A crucial challenge is simulating the network of remote sensors meteorologists use to detect wind speeds before a hurricane makes landfall. The same system does not exist in the Pacific to measure likely rainfall, but Jackson said NWS is working on new technologies.

"We're in the very early stages of a work in progress," he said.

Click here to link to the ARkStorm report.

Sullivan reported from San Francisco.

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