Erica Hupp/Dwayne Brown
Headquarters, Washington
202-358-1237/1726
Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0474
RELEASE: 06-370
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 GRACE'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, 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 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.
Matt Rodell, a hydrologist at NASA's Goddard Space Flight Center,
Greenbelt, Md., said GRACE 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."
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.
GRACE'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, Calif.
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 about GRACE, see:
http://www.csr.utexas.edu/grace/
For more on NASA water and energy cycle research, visit:
http://watercycle.gsfc.nasa.gov/index.php
Other media contacts: Margaret Baguio, University of Texas Center for
Space Research, Austin, 512-471-6922; Jennifer Fitzenberger,
University of California, Irvine, 949-824-3969.
-end-
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