Satellite data shows recent changes in Earth’s freshwater distribution

Satellite data shows recent changes in Earth’s freshwater distribution


Washington, December 12, 2006 – 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.

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.

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.

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.

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.

– About GRACE
Launched in March 2002, the GRACE mission accurately maps variations in the Earth’s gravity field. The GRACE mission has two identical spacecrafts flying about 220 kilometers apart in a polar orbit 500 kilometers above the Earth.

GRACE is able to map the Earth’s gravity fields by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. It provides scientists from all over the world with an efficient and cost-effective way to map the Earth’s gravity fields with unprecedented accuracy. The results from this mission yield crucial information about the distribution and flow of mass within the Earth and it’s surroundings.

The gravity variations that GRACE studies include: changes due to surface and deep currents in the ocean; runoff and ground water storage on land masses; exchanges between ice sheets or glaciers and the oceans; and variations of mass within the Earth. Another goal of the mission is to create a better profile of the Earth’s atmosphere.

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: