August 12, 2009

Satellites study India’s vanishing water

Scientists using satellite data say they've determined northern India's groundwater has been declining by as much as 1 foot per year during the past decade.

The researchers, led by Matt Rodell of NASA's Goddard Space Flight Center, blame the water loss nearly entirely on human activity.

Hydrologists said they determined more than 26 cubic miles of groundwater disappeared from aquifers in areas of Haryana, Punjab, Rajasthan and India's capitol territory of Delhi between 2002 and 2008. That's enough water to fill Lake Mead -- the largest man-made reservoir in the United States -- three times.

Rodell's team said it found northern India's underground water supply is being pumped and consumed by human activities, such as irrigation, and it's draining aquifers faster than natural processes can replenish them.

The finding is based on data from NASA's Gravity Recovery and Climate Experiment -- 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 300 miles above Earth's surface, their positions change relative to each other in response to variations in the pull of gravity, NASA said.

Changes in underground water masses affect gravity enough to provide a signal that can be measured by the spacecraft.

The research is reported in the journal Nature.