Satellites Unlock Secret to Northern India's Vanishing Water

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Steve Cole 202-358-0918
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Sarah DeWitt 301-286-0535
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NEWS RELEASE: 2009-124 August 12, 2009

Satellites Unlock Secret to Northern India's Vanishing Water

PASADENA, Calif. – Using NASA satellite data, scientists have found that groundwater levels in
northern India have been declining by as much as 33 centimeters (1 foot) per year over the past
decade. Researchers concluded the loss is almost entirely due to human activity.

More than 108 cubic kilometers (26 cubic miles) of groundwater disappeared from aquifers in areas of
Haryana, Punjab, Rajasthan and the nation's capitol territory of Delhi, between 2002 and 2008. This is
enough water to fill Lake Mead, the largest man-made reservoir in the United States, three times.

A team of hydrologists led by Matt Rodell of NASA's Goddard Space Flight Center in Greenbelt,
Md., found that northern India's underground water supply is being pumped and consumed by
human activities, such as irrigating cropland, and is draining aquifers faster than natural processes can
replenish them. The results of this research were published today in Nature.

The finding is based on data from NASA's Gravity Recovery and Climate Experiment (Grace), a pair
of satellites that sense changes in Earth's gravity field and associated mass distribution, including
water masses stored above or below Earth's surface. As the twin satellites orbit 483 kilometers (300
miles) above Earth's surface, their positions change relative to each other in response to variations in
the pull of gravity.

Changes in underground water masses affect gravity enough to provide a signal that can be measured
by the Grace spacecraft. After accounting for other mass variations, such changes in gravity are
translated into an equivalent change in water.

"Using Grace satellite observations, we can observe and monitor water storage changes in critical
areas of the world, from one month to the next, without leaving our desks," said study co-author
Isabella Velicogna of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and the University of
California, Irvine.

Groundwater comes from the natural percolation of precipitation and other surface waters down
through Earth's soil and rock, accumulating in cavities and layers of porous rock, gravel, sand or clay.
Groundwater levels respond slowly to changes in weather and can take months or years to replenish
once pumped for irrigation or other uses.

Data provided by India's Ministry of Water Resources to the NASA-funded researchers suggested
groundwater use across India was exceeding natural replenishment, but the regional rate of depletion
was unknown. Rodell and colleagues analyzed six years of monthly Grace data for northern India to
produce a time series of water storage changes beneath the land surface.

"We don't know the absolute volume of water in the northern Indian aquifers, but Grace provides
strong evidence that current rates of water extraction are not sustainable," said Rodell. "The region
has become dependent on irrigation to maximize agricultural productivity. If measures are not taken
to ensure sustainable groundwater usage, the consequences for the 114 million residents of the region
may include a collapse of agricultural output and severe shortages of potable water."

Researchers examined data and models of soil moisture, lake and reservoir storage, vegetation and
glaciers in the nearby Himalayas in order to confirm that the apparent groundwater trend was real.
The loss is particularly alarming because it occurred when there were no unusual trends in rainfall. In
fact, rainfall was slightly above normal for the period. The only influence they couldn't rule out was
human.

"For the first time, we can observe water use on land with no additional ground-based data
collection," said co-author James Famiglietti of the University of California, Irvine. "This is critical
because in many developing countries, where hydrological data are both sparse and hard to access,
space-based methods provide perhaps the only opportunity to assess changes in fresh water
availability across large regions."

Grace is a partnership between NASA and the German Aerospace Center, DLR. JPL developed the
twin Grace satellites. The University of Texas Center for Space Research in Austin has overall Grace
mission responsibility. Grace was launched in 2002.

For more information, please visit: http://www.nasa.gov/topics/earth/features/india_water.html .

For more information about NASA and agency programs, visit: http://www.nasa.gov .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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