[env-trinity] Study: State drought worst in millennium Tree rings dating back to 800 A.D. analyzed

[Tom Stokely]

http://www.mercurynews.com/drought/ci_27070897/california-drought-worst-1-200-years-new-study



By Paul Rogers

San Jose Mercury News progers at mercurynews.com 

The last three years of drought
 were the most severe that California  has experienced in at least 1,200
 years, according to a new scientific study published Thursday.

The study provides the state with breathtaking new historical  context 
for its low reservoirs and sinking water tables, even as California 
celebrated its first good soaking of the season.

Analyzing tree rings that dateback to 800 A.D. — a time when Vikings were marauding Europe and the 
Chinese were inventing gunpowder — there is no threeyear  period when 
California’s rainfall has been as low and its temperatures as hot as 
they have been from 2012 to 2014, the researchers  found.

“We 
were really surprised. We didn’t expect this,” said one of the study’s 
authors, Daniel Griffin,  an assistant professor in the University of 
Minnesota’s department  of geography, environment and society.

DROUGHTPAGE5 

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California’s drought-ravaged reservoirs are running so low that state 
water deliveries to some metropolitan areas have all but stopped, and 
cutbacks are forcing growers to fallow fields.


The report, published in the journal of the American  Geophysical 
Union, was written by researchers at Massachusetts’ Woods Hole 
Oceanographic Institution  and the University of Minnesota. 

The scientists measured tree rings from 278 blue oaks in central and 
Southern  California. Tree rings show the age of trees, and their width 
shows how wet each year was because trees grow more during wet years. 

The researchers compared  the information to a database of other tree 
ring records from longer-living trees like giant sequoias and 
bristlecone pines, dating  back 1,200 years. 

Meanwhile, the rain that California received this week provided a 
promising start to a winter that water  managers say needs to be 
relentless and drenching to break the drought cycle. 

“It’s a good beginning,” said Art Hinojosa, chief of hydrology at the 
state Department of Water Resources.  “But we need storm after storm 
after storm if we have any hope of getting  out of the drought this 
year.” 

By April, he said, 
California  needs at least eight more major storm systems like the one 
this week — as well as many smaller systems  — to fill its dangerously  
low reservoirs and break the drought. Rain and snow this winter needs to be at least 150 percent of average for the reservoirs to fill, Hinojosa said. 

This week’s storm was the 
biggest to hit California in roughly two years. Many parts of the state 
received between 2 and 4 inches of rain, doubling or tripling their 
totals since July. 

More important, 
several  of the state’s large reservoirs  began to receive moderate 
amounts of runoff,  as the parched ground became saturated. Lake Shasta 
gained about 6,000 acre-feet through midnight Wednesday, and Oroville 
Reservoir in Butte County added 17,000 acre-feet. But that new water 
boosted Shasta’s storage by less than 1 percent, leaving it at only 23 
percent full. It added 3 percent at Oroville, which is now 26 percent 
full, the lowest level in its history for this time of year. 

The Sierra snowpack told a similar story. A week ago, it was at 24 
percent of the average for this time of year. Thursday, after a week of 
snow, it was at 39 percent — still far below normal. 

But more rain and snow is on the way. 

The Weather Service issued  a report late Thursday  saying that 
because of storms brewing as far away as Hawaii, projections out to Dec. 18 show that “wetter  than normal conditions are favored.” 

Experts emphasize that a three-year drought cannot be erased in a few 
days. Not only are reservoirs low, but there are huge “rainfall 
deficits”  built up from the past three years. 

Overall, 94 percent of California remains in “severe  drought,” 
according to Thursday’s edition of the Federal Drought Monitor, a weekly report from the U.S. Department of Agriculture and other agencies. 

It was the tree-ring study showing California suffering  its worst 
drought in 1,200 years, however, that received the most attention 
Thursday. 

The researchers took core samples, which don’t harm the living trees, of oaks as old as 500 years and oak logs dating back more than 700 years, the University of 
Minnesota’s Griffin said. And they sanded down the wood with extremely 
finegrain  sandpaper, magnifying  the rings 40 times under  a microscope and measuring  them to within one one-thousandth of a millimeter. 

They then compared the findings to the North American  Drought Atlas, a detailed  collection of other tree-ring data that goes back 1,200 years and includes  measurements from ancient trees such as giant sequoias 
and bristlecone pines. The atlas calculates temperature and rainfall for those years by comparing  the tree rings with tree rings from the past 
100 years, when modern records were kept.  Although there are 37 times 
over the past 1,200 years when there were three-year dry periods in 
California, no period had as little rainfall and as hot of temperatures 
as 2012-14, the scientists concluded. 

With climate change already  warming the earth, the last three years 
in California  could become a more recurring event, they said. 

“This kind of drought is what we expect to see more of in the future,” said Griffin.  “Maybe the future is now.” Mercury News staff writer David E. Early contributed  to this report. 
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