NASA Data Reveal Major Groundwater Loss in California
December 14, 2009
PASADENA,
Calif. – New space observations reveal that since October 2003, the
aquifers for California's primary agricultural region -- the Central
Valley -- and its major mountain water source -- the Sierra Nevadas --
have lost nearly enough water combined to fill Lake Mead, America's
largest reservoir. The findings, based on data from the NASA/German
Aerospace Center Gravity Recovery and Climate Experiment (Grace),
reflect California's extended drought and increased rates of
groundwater being pumped for human uses, such as irrigation.
In
research being presented this week at the American Geophysical Union
meeting in San Francisco, scientists from NASA and the University of
California, Irvine, detailed California's groundwater changes and
outlined Grace-based research on other global aquifers. The twin Grace
satellites monitor tiny month-to-month changes in Earth's gravity field
primarily caused by the movement of water in Earth's land, ocean, ice
and atmosphere reservoirs. Grace's ability to directly 'weigh' changes
in water content provides new insights into how Earth's water cycle may
be changing.
Combined, California's Sacramento and San Joaquin
drainage basins have shed more than 30 cubic kilometers of water since
late 2003, said professor Jay Famiglietti of the University of
California, Irvine. A cubic kilometer is about 264.2 billion gallons,
enough to fill 400,000 Olympic-size pools. The bulk of the loss
occurred in California's agricultural Central Valley. The Central
Valley receives its irrigation from a combination of groundwater pumped
from wells and surface water diverted from elsewhere.
"Grace data
reveal groundwater in these basins is being pumped for irrigation at
rates that are not sustainable if current trends continue," Famiglietti
said. "This is leading to declining water tables, water shortages,
decreasing crop sizes and continued land subsidence. The findings have
major implications for the U.S. economy, as California's Central Valley
is home to one sixth of all U.S. irrigated land, and the state leads
the nation in agricultural production and exports."
"By providing
data on large-scale groundwater depletion rates, Grace can help
California water managers make informed decisions about allocating
water resources," said Grace Project Scientist Michael Watkins of
NASA's Jet Propulsion Laboratory, Pasadena, Calif., which manages the
mission for NASA's Science Mission Directorate, Washington.
Preliminary
studies show most of the water loss is coming from the more southerly
located San Joaquin basin, which gets less precipitation than the
Sacramento River basin farther north. Initial results suggest the
Sacramento River basin is losing about 2 cubic kilometers of water a
year. Surface water losses account for half of this, while groundwater
losses in the northern Central Valley add another 0.6 cubic kilometers
annually. The San Joaquin Basin is losing 3.5 cubic kilometers a year.
Of this, more than 75 percent is the result of groundwater pumping in
the southern Central Valley, primarily to irrigate crops.
Famiglietti
said recent California legislation decreasing the allocation of surface
waters to the San Joaquin Basin is likely to further increase the
region's reliance on groundwater for irrigation. "This suggests the
decreasing groundwater storage trends seen by Grace will continue for
the foreseeable future," he said.
The California results come just
months after a team of hydrologists led by Matt Rodell of NASA's
Goddard Space Flight Center, Greenbelt, Md., found groundwater levels
in northwest India have declined by 17.7 cubic kilometers per year over
the past decade, a loss due almost entirely to pumping and consumption
of groundwater by humans.
"California and India are just two of many
regions around the world where Grace data are being used to study
droughts, which can have devastating impacts on societies and cost the
U.S. economy $6 to $8 billion annually," said Rodell. Other regions
under study include Australia, the Middle East – North Africa region
and the southeastern United States, where Grace clearly captured the
evolution of an extended drought that ended this spring. In the Middle
East – North Africa region, Rodell is leading an effort to use Grace
and other data to systematically map water- and weather-related
variables to help assess regional water resources. Rodell added Grace
may also help predict droughts, since it can identify pre-existing
conditions favorable to the start of a drought, such as a deficit of
water deep below the ground.
NASA is working with the National
Oceanic and Atmospheric Administration and the University of
Nebraska-Lincoln to incorporate Grace data into NOAA's U.S. and North
American Drought Monitors, premier tools used to minimize drought
impacts. The tools rely heavily on precipitation observations, but are
limited by inadequate large-scale observations of soil moisture and
groundwater levels. "Grace is the only satellite system that provides
information on these deeper stores of water that are key indicators of
long-term drought," Rodell said.
Grace is a partnership of NASA and
the German Aerospace Center (DLR). The University of Texas Center for
Space Research, Austin, has overall mission responsibility. JPL
developed the satellites. DLR provided the launch, and
GeoForschungsZentrum Potsdam, Germany, operates the mission. For more
on Grace, see http://www.csr.utexas.edu/grace/ and
http://grace.jpl.nasa.gov/ . Other media contacts: Margaret Baguio,
University of Texas Center for Space Research, 512-471-6922; Jennifer
Fitzenberger, University of California, Irvine, 949-824-3969.
The
combined Sacramento River, San Joaquin River and Tulare Lake Basins
cover an area of approximately 154,000 square kilometers. They include
California's major mountain water source, the snowpack in the Sierra
Nevada mountain range; and the Central Valley, the state's primary
agricultural region.
Since the Gravity
Recovery and Climate Experiment sees
all the water storage changes on land, in order to estimate the
groundwater in storage change signal, the snow, surface water and soil
moisture mass changes must be estimated and removed.
Data
gathered from October 2003 through March 2009 was analyzed. The results
showed that water stored in the combined Sacramento River, San
Joaquin River, and Tulare Lake Basins decreased by more than 31 cubic kilometers (8.2 trillion gallons or
25,134,008 acrefeet),
or nearly the volumne of Lake Mead. Nearly two-thirds of this came from
changes in groundwater storage, primarily from the Central Valley.
Gravity Recovery and
Climate Experiment observed
ground water trends in the Sacramento and San Joaquin River basins,
Oct. 2003 to March 2009.
Jet
Propulsion Laboratory is managed for NASA by the California Institute
of Technology in Pasadena.
Link to NASA News page: http://www.jpl.nasa.gov/news/
