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@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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