We all know about the deal you make with earthquakes to live in California. They are going to happen, maybe even a horrifically big one, so we try to prepare and we learn to wake up when the first energy wave enters the bedroom. But the worst catastrophes to hit California since statehood were actually storms. Wet Pacific storms that seem to never end, and that cause massive flooding. Even with all the dams and river channels that have tamed ordinary runoff, we're mostly defenseless against the mega-storms that the Pacific has sent our way every 200 years or so.
Forget the storm sieges you may have lived through, with their mud slides and flooded streets and "Storm Watch" chirons, and even the historic 1938 flood that remade the landscape and civic culture of Los Angeles. The last real big event on the epic scale we're talking about came during the winter of 1861-62. It lasted 43 days, killed thousands of people, drowned 800,000 cattle, and left the state of California bankrupt.
A package of stories and graphics in this months's Scientific American, pegged to a book coming from UC Press, says the next one will hurt more.
A comparable episode today would be incredibly more devastating. The Central Valley is home to more than six million people, 1.4 million of them in Sacramento. The land produces about $20 billion in crops annually, including 70 percent of the world’s almonds—and portions of it have dropped 30 feet in elevation because of extensive groundwater pumping, making those areas even more prone to flooding. Scientists who recently modeled a similarly relentless storm that lasted only 23 days concluded that this smaller visitation would cause $400 billion in property damage and agricultural losses. Thousands of people could die unless preparations and evacuations worked very well indeed.
Co-author B. Lynn Ingram says these events through history have begun in the tropical Pacific Ocean. They build into a narrow stream of water vapor racing around the globe about a mile above the sea and extending for thousands of kilometers. "Recent research describes these storms more broadly as 'atmospheric rivers,' and they often result in the worst floods in not only the American West, but across the globe," the story says.
The upcoming book, with Frances Malamud-Roam, is "The West Without Water: What Past Floods, Droughts, and Other Climatic Clues Tell Us About Tomorrow" (University of California Press, Spring 2013.)