Satellites unlock secret to northern India's vanishing water

Jet Propulsion Laboratory, NASA: 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.

…."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.”….

NASA's Grace satellites measured the depletion of groundwater in northwestern India between 2002 and 2008. Image credit: NASA/Trent Schindler and Matt Rodell