Needed: 11 Trillion Gallons to Replenish California Drought
 
Dec. 16, 2014: It will take about 11 trillion gallons of water (42 cubic
kilometers) -- around 1.5 times the maximum volume of the largest U.S.
reservoir -- to recover from California's continuing drought, according to
a new analysis of NASA satellite data.
 
The finding was part of a sobering update on the state's drought made
possible by space and airborne measurements and presented by NASA
scientists Dec. 16 at the American Geophysical Union meeting in San
Francisco. Such data are giving scientists an unprecedented ability to
identify key features of droughts, data that can be used to inform water
management decisions.
 
A team of scientists led by Jay Famiglietti of NASA's Jet Propulsion
Laboratory in Pasadena, California used data from NASA's Gravity Recovery
and Climate Experiment (GRACE) satellites to develop the first-ever
calculation of this kind -- the volume of water required to end an episode
of drought.
 
http://www.nasa.gov/mission_pages/Grace/index.html
 
NASA satellite data reveal the severity of California's drought on water
resources across the state. This map shows the trend in water storage
between September 2011 and September 2014. Image Credit: NASA JPL
 
Earlier this year, at the peak of California's current three-year drought,
the team found that water storage in the state's Sacramento and San Joaquin
river basins was 11 trillion gallons below normal seasonal levels. Data
collected since the launch of GRACE in 2002 shows this deficit has
increased steadily.
 
"Spaceborne and airborne measurements of Earth's changing shape,
surface height and gravity field now allow us to measure and analyze key
features of droughts better than ever before, including determining
precisely when they begin and end and what their magnitude is at any moment
in time," Famiglietti said. "That's an incredible advance and
something that would be impossible using only ground-based
observations."
 
GRACE data reveal that, since 2011, the Sacramento and San Joaquin river
basins decreased in volume by four trillion gallons of water each year (15
cubic kilometers). That's more water than California's 38 million residents
use each year for domestic and municipal purposes. About two-thirds of the
loss is due to depletion of groundwater beneath California's Central
Valley.
 
In related results, early 2014 data from NASA's Airborne Snow Observatory
indicate that snowpack in California's Sierra Nevada range was only half of
previous estimates.
 
The observatory is providing the first-ever high-resolution observations of
snow water volume in the Tuolumne River, Merced, Kings and Lakes basins of
the Sierra Nevada and Uncompahgre watershed in the Upper Colorado River
Basin.
 
To develop these calculations, the observatory measures how much water is
in the snowpack and how much sunlight the snow absorbs, which influences
how fast the snow melts. These data enable accurate estimates of how much
water will flow out of a basin when the snow melts, which helps guide
decision about reservoir filling and water allocation.
 
"The 2014 snowpack was one of the three lowest on record and the worst
since 1977, when California's population was half what it is now,"
said Airborne Snow Observatory principal investigator Tom Painter of JPL.
"Besides resulting in less snow water, the dramatic reduction in snow
extent contributes to warming our climate by allowing the ground to absorb
more sunlight. This reduces soil moisture, which makes it harder to get
water from the snow into reservoirs once it does start snowing again."
 
New drought maps show groundwater levels across the U.S. Southwest are in
the lowest two to 10 percent since 1949. The maps, developed at NASA's
Goddard Space Flight Center in Greenbelt, Maryland, combine GRACE data with
other satellite observations.
 
"Integrating GRACE data with other satellite measurements provides a
more holistic view of the impact of drought on water availability,
including on groundwater resources, which are typically ignored in standard
drought indices," said Matt Rodell, chief of the Hydrological Sciences
Laboratory at Goddard.
 
The scientists cautioned that while the recent California storms have been
helpful in replenishing water resources, they aren't nearly enough to end
the multi-year drought.
 
"It takes years to get into a drought of this severity, and it will
likely take many more big storms, and years, to crawl out of it," said
Famiglietti.
 
 
Credits and more information:
Production editor: Dr. Tony Phillips | Credit: Science{at}NASA
 
NASA monitors Earth's vital signs from land, air and space with a fleet of
satellites and ambitious airborne and ground-based observation campaigns.
The agency develops new ways to observe and study Earth's interconnected
natural systems with long-term data records and computer analysis tools to
better see how our planet is changing. The agency shares this unique
knowledge with the global community and works with institutions in the
United States and around the world that contribute to understanding and
protecting our home planet.
 
For more information on GRACE, visit http://www.nasa.gov/grace and
http://www.csr.utexas.edu/grace
 
For more on the Airborne Snow Observatory, visit: http://aso.jpl.nasa.gov/
 
For more information about NASA's Earth science activities, visit:
http://www.nasa.gov/earthrightnow
 
 
Regards,
 
Roger

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