Historical perspective on California megadroughts

How might the historical grasp of the frequency of megadroughts in California influence our decision on the water bond, with its funds for the construction of tunnels beneath the Delta to ship the fresher Sacramento River water to the great north-south canals?
For some, it make make the bond even more imperative than it already is for them. At any cost to the environmental and -- increasingly -- to the society, capitalism in California must continue following the path to the greatest return on investment -- real estate development, either residential or -- also increasingly -- in agribusiness. Another player in the merry dance of natural resource destruction in the state is hydraulic fracturing drilling for oil and gas, which uses enormous quantities of water and pollutes groundwater wherever it is established.
Others, perhaps more thoughtful people, and those who possess some connection with Nature not entirely committed to commercial exploitation and destruction, might take a different view.  Or, simply that that portion of the vast majority of Californians that don't have much of any connection to Nature, exploitive or otherwise, but who are just not subject to being bullied by the fear mongering of the usual financial, insurance and real estate special interests. 
How will this latter group vote, in view of the historical evidence of frequent megadroughts in the state's past, the inevitability of more of them, and those coming more and more frequently due to global warming?
Respecting the limits that Natutre places on all life in California may not make one wealthier, but it makes life richer. -- blj

 10-10-14
San Diego Union-Tribune
A history of megadrought
By Deborah Sullivan Brennan
 http://www.utsandiego.com/news/2014/oct/10/environment-san-diego-megadro...

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Weather in the West has always been a wild ride of long dry years punctuated on occasion by torrential floods.
“Our history is written in great droughts in California,” said Bill Patzert, a climate scientist at NASA’s Jet Propulsion Laboratory in Pasadena. “It’s a semi-arid place. It’s mostly dry, not mostly wet.”
That’s been the case for most of the past decade and a half. Recent ocean cooling events, including La Nina and the Pacific Decadal Oscillation, a decades-long cycle of ocean temperatures, have pushed storms northward, dumping rain and snow at higher latitudes and leaving the Southwest dry.
“The oceans tend to act as a flywheel, steering climates for decades at a time,” said Greg Pederson, a research ecologist with the U.S. Geological Survey, who co-authored this month's megadrought study with researchers from the U.S. Geological Survey.
Reliable rainfall records don’t go back much further than the last century, but tree rings and lake beds tell the story of nature’s fickle habits.
Trees lap up moisture when it’s plentiful, using extra rain to grow thicker trunks. That leaves an annual pattern of rings that act as a “proxy record” of each year’s rainfall.
Sunken forests also reveal climate history; ancient stumps in mountain lakes show where the waters had receded in other eras, allowing forests to grow in areas now under water.
 “Between 6,300 years ago and 4,800 years ago, it was warmer but it was also drier in California and the West,” said Lynn Ingram, a professor of earth and planetary science at UC Berkeley. “Lake Tahoe went down 20 feet. Mono Lake and Owens Lake were reduced.”
Tulare Lake, the shallow, 600-square-mile lake that once saturated part of the southern San Joaquin Valley, dried up entirely.
The medieval period, between 900 and 1300 AD was also interspersed with decades-long dry periods when precipitation in the West dropped to about 60 percent of our 20th century average, she said.
Those records show the natural changeability of water in the West. And then there’s climate change, pushing the region’s water cycle into overdrive.
“To have a megadrought we don’t need climate change,” said Alexander Gershunov, a research meteorologist at Scripps Institution of Oceanography in La Jolla who studies climate variability. “Megadroughts have happened over the last few centuries before we had measurements, and they can certainly happen again. Climate change makes them a little more likely.”
The warming could also increase evaporation, escalating the demand for water as supplies become less reliable, he said. The extra heat could also trigger more frequent dry spells, causing droughts that happened once a century to recur more often.
“What used to be a 100-year drought may become a 50- or a 30-year drought in the coming decades,” Gershunov said.