India's thirst is making us all wet

New Scientist 3 Oct 09;

ONE nation's thirst for groundwater is having an impact on global sea levels. Satellite measurements show that northern India is sucking some 54 trillion litres of water out of the ground every year. This is threatening a major water crisis and adding to global sea level rise.

Virendra Tiwari from the National Geophysical Research Institute in Hyderabad, India, and colleagues used gravity data from the GRACE satellite to monitor the loss of continental mass around the world since 2002. Regions where water is being removed from the ground have less mass and therefore exert a smaller gravitational pull on the satellite.

The data revealed that groundwater under northern India and its surroundings is being extracted exceptionally fast. Tiwari and colleagues calculate that between 2002 and 2008 an average of 54 cubic kilometres - enough to fill more than 21 million Olympic swimming pools - was lost every year. Boreholes in the region show the water table is dropping by around 10 centimetres a year (Geophysical Research Letters, DOI: 10.1029/2009gl039401).

Agriculture is the primary culprit, says John Wahr of the University of Colorado at Boulder. If the trend isn't reversed soon, the 600 million people living in the region could face severe water shortages in the next few years.

The "lost" water doesn't just disappear, though. Most of it runs into the oceans. The team calculates that it could be pushing up global sea levels by as much as 0.16 millimetres each year. That's 5 per cent of total sea level rise.