Satellites Unlock Secret to Vanishing Water
Using NASA satellite data, scientists have found that groundwater levels in Northern India have been declining by as much as one foot per year over the past decade. Researchers concluded the loss is almost entirely due to human activity.
More than 26 cubic miles of groundwater disappeared from aquifers in areas of Haryana, Punjab, Rajasthan and the nation's capital 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 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 normal processes can replenish them.
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 the 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.
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.