The other Big One

by Judith Lewis

Updated 2/16/10

The year 1862 began with a storm. It had been raging in Utah Territory for a week already, and John D. Lee, a Mormon bishop and president of the Harmony branch of the church, meticulously recorded its effects: How eight inches of snow fell one day only to wash away in the night's battering rain; how the swollen Rio Virgin made off with a neighbor's "house, Cane mill, (and) Blacksmith shop," plus 150 gallons of molasses. Lee tracked the shifting winds and noted the weather they brought with them; he measured the waters that rose in his basement and counted the days without sun (28 and a half as of Jan. 31). Even when two of his children were killed on Feb. 6, he carefully noted that the wind that blew down the wall that crushed them had gusted straight and sudden out of the north.

Perhaps Lee saw the storm as God's punishment. He was already a fugitive, a man who just five years earlier had participated in -- some say led -- the slaughter of 120 emigrants at Mountain Meadows. But if God was indeed unleashing His wrath, it wasn't upon Lee alone. As Lee moved his clan from one crumbling fort to the next, hoping to find walls to protect his 10 wives and their brood, settlers all along the western flank of North America were cowering under storms more intense and enduring than any of them had ever known. Rivers were changing course, the Pacific coast was changing shape, small towns along riverbanks were floating away in floodwaters. From British Columbia to the Mexican border, hundreds of thousands of people were struggling to bear up against blasting winds triggered by fast-moving air streaming up from the tropics, and carrying enough moisture to turn California's inland valleys into lakes.

The western edge of this continent has not felt a winter so devastating since. "It was the West's Katrina," says Cary Mock, a professor of geography at the University of South Carolina and student of the 1862 storms. But something that brought catastrophe once is likely to do so again. Only this time, millions of city dwellers will be at the mercy of engineered environments: New suburbs planted in floodplains; dream homes perched on precarious hillsides; long, heavily traveled bridges.

Marty Ralph, a research meteorologist with the National Oceanic and Atmospheric Administration in Boulder, Colo., blames 1862's bad weather on a phenomenon called an "atmospheric river." Unlike the jet stream, which moves extremely cold, dry air 30,000 feet above us, atmospheric rivers flow at altitudes of around 2,000 to 6,000 feet, pushing warm equatorial water vapor toward the poles. Shorter-lived systems of various intensities hit the West Coast a couple of dozen times a year, and they do have an upside: "Atmospheric rivers produce half the water supply of California," Ralph says. "A few big storms feed the snowpack that fills the region's reservoirs."

But once in a while -- no one knows why -- an atmospheric river comes on especially fierce and stalls when it hits the coast. In 1969, 21 inches of rain fell on Los Angeles in a single day; in 1986, an atmospheric river dumped 41 inches on the Northern Sierras in less than a week. That may be what happened for an extended period in 1862, says hydrologist and climate expert Mike Dettinger of Scripps Institution of Oceanography in La Jolla, Calif. "Or it may have been a string of storms, back to back -- or it could be both." The effect is pretty much the same, he says: "A month of unbroken rain."

In an effort to come to grips with the civic consequences should an 1862-type storm come again, the U.S. Geological Survey launched the "ARkStorm" project, the second phase of a five-year effort to assess the threat of various natural disasters, specifically in California. "The idea," says project manager Dale Cox, "is to bring people together around a big-concept storm and get them thinking about it in a way they otherwise wouldn't. Where would the worst flooding be? Where would landslides and debris flows occur? What systems do we depend on that lie in the path of those areas?

"This way we get a chance to ask in advance, ‘What do I need to do to prepare?' "

In 2008, Cox recruited Ralph and Dettinger to draw up a hypothetical "Frankenstorm." The two collaborators then convened a panel of experts in February 2009 -- meteorologists, climatologists, hydrologists -- and for three days they brainstormed about how to use recent data to craft an 1862-level storm. "We took a modern storm that was focused in Southern California, and another focused on Northern California and strung them end to end," Dettinger explains. "And because we see in the record all the time that these winter storms stall for anywhere from a few hours to a day, we took the Southern California part of the storm -- one that actually happened on Jan. 19, 1969 -- and allowed it to stall."

It's not quite the storm of 1862, Ralph admits: "We dialed it back a bit." Still, the computer models gave them three solid weeks of rain.

"Everything was in trouble by that time," Dettinger says. "We had massive flooding everywhere."

From there, ARkStorm is in part a mathematical problem, measuring how much rainfall will overtop a levee here, how much moisture will collapse a hillside there. But natural systems seldom follow a neatly engineered order, and human beings very rarely do.

That's where anecdotal accounts like Lee's come in: In the same way the USGS collects information from the public after an earthquake on its "Did You Feel It?" Web site, Cox wanted first-hand accounts to figure into ARkStorm's data set. "There's so much that's not known about these past storms," he says. "In 1861-1862, there were four rain gauges in the whole country." And so he contacted Cary Mock, who had been working with graduate student Stephanie Dodds to recreate an 1880 hurricane that happened in Sitka, Alaska, using ships' logbooks.

"I told him, ‘We're going to create our own storm, and I'd like to know what the storm actually did,' " Cox recalls. "And I come to find Cary Mock had been collecting stories about 1862 since 1988."

Mock is a paleoclimatologist: He studies weather patterns over the Earth's entire history, and uses them to forecast meteorological patterns in the future. With the information he gathers from old instrumental records, newspaper reports and personal diaries, he draws weather maps similar to the kind used by television weather people, only for weather events that happened long before radar was around to analyze Doppler effects and bow echoes. Lee's diary helped Mock grasp the extent of the turmoil: "It's hard to say that the winter storms of 1862 were unprecedented if you just pinpoint one location," he says. "But in terms of how widespread it was, nothing we have in the historical record even comes close."

In the Washington Territories, reported the Olympia Overland Press, "It raineth every day, and every night also." In Nevada, according to a letter-writer named Uriah Allen, the Carson River turned the Carson Valley into a "muddy lake," and "all the bridges upon the rivers were washed away." An assiduous California diarist named Alfred Doten reported that "the water covers all Sacramento Valley, & the cattle are dying in droves -- they stand in 2 or 3 ft of water, in huddles & starve to death -- no chance to save them." Farther south, an entire town, christened Agua Mansa for the formerly gentle waters of the Santa Ana River, completely disappeared -- a calamity documented in the diary of a regional judge named Benjamin Hayes. Hayes recalled the local priest frantically ringing the church bell to call the townspeople to higher ground. Miraculously, no one was killed.

How will modern dams, river channels and levees -- most of which are built only to handle 50-year floods -- fare when waters rush out of the mountains in "billows 50 feet high," as one diarist described it? Keith Porter, a structural engineer at the University of Colorado at Boulder, suggests that an 1862-type storm could cause 300 miles of flooding in California's Central Valley, with waterways anywhere from 12 to 60 miles wide. And while "we're not ready to release all the detail of our flooding scenario just yet," Porter says, "we imagine large areas of Orange County will flood -- in some places several feet deep." Fuel lines, aqueducts, interstate highway bridges would all be vulnerable to failure.

It's too soon in the ARkStorm process to predict the extent of the suffering an extended atmospheric river would cause in California's most vulnerable region -- the increasingly fragile California Bay-Delta, at the confluence of the state's two largest rivers. But we can begin to imagine it: In Marc Reisner's A Dangerous Place: California's Unsettling Fate, the author hypothesized what would happen if an earthquake on the Hayward Fault under Oakland caused the Delta's levees to fail. If the earthquake hit in the spring, "with the Sacramento River carrying most of the Sierra Nevada's runoff," 10,000 acres of dry land would be "filled to sea level in a couple of hours." As other levees failed in turn, seawater would push into the Delta, contaminating the source of half the state's drinking water. A catastrophic flood would have the same effect.

So what's a public policy planner to do? Can we protect our cities against the coming flood? The answer, for the most part, is no. Even though Dettinger projects that climate change may cause atmospheric rivers to hit the West Coast with increasing frequency, and despite all the promises governors have made to fix their states' infrastructure, neither federal dollars nor state budgets will be enough to shore up the walls against a once-a-century storm. "The question we're trying to answer instead," Porter says, "is: ‘What we will do to mitigate the damage in terms of coordinating emergency response?' "

The ARkStorm team has until May of 2011 to design an emergency response drill around that question. And some of the answers might turn out to be simple. Up in Sacramento, Cox talked to fire department Battalion Chief Marc Bentovoja about the possibility of the city flooding as it did in 1862. The newly elected governor, Leland Stanford, had had to travel by rowboat from San Francisco to his inauguration at the state's Capitol. "(Bentovoja's) response was, ‘I don't have enough boats,' " Cox recalls. "But the community has a lot of boats. I suggested to him that local responders might organize boats for an event. Count the boats!"

Contributing Editor Judith Lewis writes about the environment from Venice, California.

For more information, please see:

The USGS's Multihazard demonstration project, including ARkStorm.

NOAA on atmospheric rivers

Flooding from atmospheric rivers

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