California Megaflood: Lessons from a Forgotten Catastrophe

 via Scientific American. H/t to Bitsa Burger for the heads-up.

A 43-day storm that began in December 1861 put central and southern California underwater for up to six months, and it could happen again

By B. Lynn Ingram on January 1, 2013

Geologic evidence shows that truly massive floods, caused by rainfall alone, have occurred in California every 100 to 200 years. Such floods are likely caused by atmospheric rivers: narrow bands of water vapor about a mile above the ocean that extend for thousands of kilometers.

The atmospheric river storms featured in a January 2013 article in Scientific American that I co-wrote with Michael Dettinger, The Coming Megafloods, are responsible for most of the largest historical floods in many western states. The only megaflood to strike the American West in recent history occurred during the winter of 1861-62. California bore the brunt of the damage. This disaster turned enormous regions of the state into inland seas for months, and took thousands of human lives. The costs were devastating: one quarter of California’s economy was destroyed, forcing the state into bankruptcy.

Today, the same regions that were submerged in 1861-62 are home to California’s fastest-growing cities. Although this flood is all but forgotten, important lessons from this catastrophe can be learned. Much of the insight can be gleaned from harrowing accounts in diary entries, letters and newspaper articles, as well as the book Up and Down California in 1860-1864, written by William Brewer, who surveyed the new state’s natural resources with state geologist Josiah Whitney.

In 1861, farmers and ranchers were praying for rain after two exceptionally dry decades. In December their prayers were answered with a vengeance, as a series of monstrous Pacific storms slammed—one after another—into the West coast of North America, from Mexico to Canada. The storms produced the most violent flooding residents had ever seen, before or since.


Continue reading at the source.


Ingram concludes her piece,

The lessons of the 1861-62 floods should provide the impetus for flood disaster planning efforts in a region where housing developments and cities are spreading across many floodplains. A critical element of living in a place like California is an awareness of these natural disasters, which requires a deep understanding of the natural patterns and frequencies of these events. Today we have building codes for earthquake safety, but millions of new westerners are not aware of the region’s calamitous climate history. Most have never even heard of the 1861–62 floods, and those may not have been the worst that nature can regularly dish out to the region. In a forthcoming book I co-wrote with Frances Malamud-Roam, THE WEST WITHOUT WATER: What Past Floods, Droughts, and Other Climatic Clues Tell Us About Tomorrow (University of California Press, Spring 2013) we present evidence for similar if not larger floods that have occurred every one to two centuries over the past two millennia in California, as well as nature’s flip-side: deep and prolonged droughts.”

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