Scientists say past century in US west among wettest in last 7000 years, California currently in 20 year dry phase due to negative Pacific decadel oscillation and not related to global warming

1/25/14, "California drought: Past dry periods have lasted more than 200 years, scientists say," Mercury News, Paul Rogers

"California's current drought is being billed as the driest period in the state's recorded rainfall history. But scientists who study the West's long-term climate patterns say the state has been parched for much longer stretches before that 163-year historical period began....


Through studies of tree rings, sediment and other natural evidence, researchers have documented multiple droughts in California that lasted 10 or 20 years in a row during the past 1,000 years -- compared to the mere three-year duration of the current dry spell. The two most severe megadroughts make the Dust Bowl of the 1930s look tame: a 240-year-long drought that started in 850 and, 50 years after the conclusion of that one, another that stretched at least 180 years. 


"We continue to run California as if the longest drought we are ever going to encounter is about seven years," said Scott Stine, a professor of geography and environmental studies at Cal State East Bay. "We're living in a dream world."

California in 2013 received less rain than in any year since it became a state in 1850. And at least one Bay Area scientist says that based on tree ring data, the current rainfall season is on pace to be the driest since 1580 -- more than 150 years before George Washington was born. The question is: How much longer will it last?...

California, the nation's most populous state with 38 million residents, has built a massive economy, Silicon Valley, Hollywood and millions of acres of farmland, all in a semiarid area. The state's dams, canals and reservoirs have never been tested by the kind of prolonged drought that experts say will almost certainly occur again.

Stine, who has spent decades studying tree stumps in Mono Lake, Tenaya Lake, the Walker River and other parts of the Sierra Nevada, said that the past century has been among the wettest of the last 7,000 years.


Looking back, the long-term record also shows some staggeringly wet periods. The decades between the two medieval megadroughts, for example, delivered years of above-normal rainfall -- the kind that would cause devastating floods today.

The longest droughts of the 20th century, what Californians think of as severe, occurred from 1987 to 1992 and from 1928 to 1934. Both, Stine said, are minor compared to the ancient droughts of 850 to 1090 and 1140 to 1320....

Roos, who has worked at the department since 1957, said the prospect of megadroughts is another reason to build more storage -- both underground and in reservoirs -- to catch rain in wet years....

If a drought lasted decades, the state could always build dozens of desalination plants, which would cost billions of dollars, said law professor Barton "Buzz" Thompson, co-director of Stanford University's Woods Institute for the Environment.

Saudi Arabia, Israel and other Middle Eastern countries depend on desalination, but water from desal plants costs roughly five times more than urban Californians pay for water now. Thompson said that makes desal projects unfeasible for most of the state now, especially when other options like recycled wastewater and conservation can provide more water at a much lower cost....
 
Over the past 10 years, he noted, Australia has been coping with a severe drought. Urban residents there cut their water demand massively, built new supply projects and survived....

Some scientists believe we are already in a megadrought, although that view is not universally accepted.

Bill Patzert, a research scientist and oceanographer at NASA's Jet Propulsion Laboratory in Pasadena, says that the West is in a 20-year drought that began in 2000. He cites the fact that a phenomenon known as a "negative Pacific decadal oscillation" is underway -- and that historically has been linked to extreme high-pressure ridges that block storms.

Such events, which cause pools of warm water in the North Pacific Ocean and cool water along the California coast, are not the result of global warming, Patzert said....

"Long before the Industrial Revolution, we were vulnerable to long extended periods of drought. And now we have another experiment with all this CO2 in the atmosphere where there are potentially even more wild swings in there," said Graham Kent, a University of Nevada geophysicist who has studied submerged ancient trees in Fallen Leaf Lake near Lake Tahoe.

Already, the 2013-14 rainfall season is shaping up to be the driest in 434 years, based on tree ring data, according to Lynn Ingram, a paleoclimatologist at UC Berkeley. "It's important to be aware of what the climate is capable of," she said, "so that we can prepare for it." Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045."...chart above, E.R. Cook et al Earth Science Reviews, Kahler, Bay Area News Group

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1/31/14,  "California's Sierra Snowpack Only 12% of Average, a Record Low," Dr. Jeff Masters Wunderblog

"Worst California drought in 500 years?" subhead

"Megadroughts in the Western U.S. can develop from natural causes, as well, and the current pattern of cooler than average ocean temperatures in the Eastern Pacific and warmer than average ocean temperatures in the Atlantic increase the odds of drought conditions like the ones we have seen during the current megadrought. Edward Cook, director of the Tree Ring Laboratory at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., said at a presentation last month at the American Geophysical Union meeting that tree ring data show that the area of the West that was affected by severe drought in the Medieval period was much higher and much longer than the current drought. It is “indeed pretty scary,” Cook said. “One lasted 29 years. One lasted 28 years. They span the entire continental United States." Two megadroughts in the Sierra Nevada of California lasted between 100 and 200 years."...(3rd parag. under subhead)

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