December 7, 2014 - CALIFORNIA, UNITED STATES
- 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 date back to 800 A.D. -- a
time when Vikings were marauding Europe and the Chinese were inventing
gunpowder -- there is no three-year 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.
Kevin Anchukaitis collects an tree-ring sample from a 300-year old blue oak in California. 2014 image by Daniel Griffin.
"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.
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| Kevin Anchukaitis collects an tree-ring sample from a 300-year old blue oak in California. © 2014, Daniel Griffin |
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.
'Good Beginning'
"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
storms -- 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.
Above Normal
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. Through Thursday night,
San Jose received 3.79 inches, San Francisco 4.43 inches and Oakland
3.01 inches, bringing each city's rainfall to above-normal levels for
the first time this year.
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.
Next Storm
But more rain and snow is on the way.
In the Bay Area, another cold front will be moving in on Friday and
will hang around a couple of days, according to the National Weather
Service.
"There will be rain Friday night and into Saturday and
then partly clearing on Sunday," said forecaster Diana Henderson. "Then
there will be a few more showers on Monday, and the next system on the
horizon will come in at the end of next week."
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.
San Jose normally receives 42.9 inches of
rain in an average three-year period, for example. Between June 2011 and
June 2014, it received just 22.8 inches, leaving the city 20 inches
short. Similarly, San Francisco is 19 inches behind, Oakland 24 inches.
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 fine-grain 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 ancient 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."
Staff writer David E. Early contributed to this report.
Read the study
here.
-
Mercury News.