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December
12, 2006
NASA OUTLINES RECENT CHANGES
IN EARTH'S FRESHWATER DISTRIBUTION
Recent
space observations of freshwater
storage by the Gravity Recovery and Climate Experiment (Grace) are
providing a
new picture of how Earth's most precious natural resource is
distributed
globally and how it is changing.
Researchers are using the mission's almost five-year data record to
estimate
seasonal water storage variations in more than 50 river basins that
cover most
of Earth's land area. The variations reflect changes in water stored in
rivers,
lakes and reservoirs; in floodplains as snow and ice; and underground
in soils
and aquifers.
"Grace is providing a first-ever look at the distribution of freshwater
storage on the continents," said Dr. Jay Famiglietti, professor of
Earth
System Science, University
of California,
Irvine.
"With longer time series, we can distinguish long-term trends from
natural
seasonal variations and track how water availability responds to
natural
climate variations and climate change."
Several African basins, such as the Congo,
Zambezi and Nile,
show significant drying over
the past five years. In the United
States,
the Mississippi
and Colorado
River basins
show water storage increases during that time. Such information is
vital for
managing water resources in vulnerable parts of Africa and Southeast Asia, since increasing
populations and standards of living place
demands on water resources that are often unsustainable. The data can
be used
to make more informed regional water-management decisions.
The twin Grace satellites monitor tiny month-to-month changes in
Earth's
gravity field that are primarily caused by the movement of water in
Earth's
land, ocean, ice and atmosphere reservoirs. Hydrologists are analyzing
Grace
data to identify possible trends in precipitation changes, groundwater
depletion and snow and glacier melt rates, and to understand their
underlying
causes.
Dr. Matt Rodell, a hydrologist at NASA's Goddard
Space Flight
Center, Greenbelt,
Md.,
said the data correspond well with ground observations. As a result,
hydrologists can now apply Grace data in ways that will impact regional
water
management. "Grace data improve our understanding of the water cycle
and
simulations of soil moisture, snow and groundwater in computer models,"
he
said. "This is a key step toward better weather, stream flow, flood,
drought and water resource forecasts worldwide."
Dr. Michael Watkins, Grace project scientist at NASA's Jet Propulsion
Laboratory, Pasadena,
Calif.,
said Grace is the only element in
NASA's broad water cycle research program that measures changes in all
types of
water storage. "Grace detects water storage changes from Earth's
surface
to its deepest aquifers. Water can't hide from it," he said.
The mission's abilities to detect water are particularly vital for the
emerging
field of groundwater remote sensing. "Remote sensing of groundwater has
been a Holy Grail for hydrologists because it is stored beneath the
surface and
is not detected by most sensors," said Famiglietti. "Outside of the United States
and a few other developed nations, it is not well monitored. It's been
speculated that many of Earth's key aquifers are being depleted due to
over-exploitation, but a lack of data has hampered efforts to quantify
how
aquifer levels are changing and take the steps necessary to avoid
depleting
them. With additional data, such as measurements of surface water and
soil
moisture, we can use Grace to solve this problem."
Grace is also allowing scientists to estimate another key component of
the
water cycle for the first time: water discharged by freshwater streams
from
Earth's continents. Stream flow measurements are often not shared for
economic,
political or national defense reasons. Grace measurements of the total
water
discharged by continental streams are important for monitoring the
availability
of freshwater and understanding how surface water runoff from
continents
contributes to rises in global sea level.
Scientists from NASA and the University
of California,
Irvine,
are presenting their research today during the American Geophysical
Union
meeting in San
Francisco.
Grace is a partnership between NASA and the German Aerospace Center
(DLR). The
University of Texas Center for Space Research, Austin, has overall
mission
responsibility. JPL developed the two Grace satellites. DLR provided
the
launch, and the GeoForschungsZentrum Potsdam, Germany, operates the
Grace
mission.
For
more information and images, visit:
http://www.nasa.gov/vision/earth/lookingatearth/grace-20061212.html
For more
information
about GRACE, visit:
http://www.csr.utexas.edu/grace/
For
more information
on NASA's water cycle research, visit:
http://watercycle.gsfc.nasa.gov/index.php
##
Contact:
Alan Buis
NASA Jet Propulsion Laboratory
818-354-0474
alan.d.buis@jpl.nasa.gov
This text is
derived from:
http://www.nasa.gov/vision/earth/lookingatearth/grace-20061212.html
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