N India’s groundwater use raising sea levels by 5%

Northern Subcontinent Pumping Out 54Tn Litres Every Year

The amount of groundwater pumped out by Delhiites and others across northern India is highest in the world

New Delhi: The amount of groundwater pumped out by Delhiites and others across northern India is highest in the world and is contributing as much as 5% to the total rise in sea levels.
    A new study using satellite data has found that the region — a swathe of over 2,000km from west Pakistan to Bangladesh along north India — extracts a mindboggling 54 trillion litres from the ground every year, a figure that’s likely to cause serious concern over the future of water availability.
    The study, conducted by Virendra Mani Tiwari from National Geophysical Research Institute in Hyderabad, along with scientists from University of Colorado, US, found that the average depletion of groundwater level in the Indian part of the region was an alarming 10cm a year.
    ‘‘We found the region of maximum groundwater loss centred around Delhi and included Rajasthan, Punjab, Haryana and west Uttar Pradesh,’’ Tiwari told TOI. The study was published on September 17, 2009 in the prestigious USbased Geophysical Research Letter.
    The research for the first time puts hard numbers to the water loss due to groundwater extraction in the region that’s home to around 10% of humanity. And the scenario is scary. The study found that the net loss of ground water was around 25 trillion litres a year.
    The water that is pumped out eventually reaches the sea through rainfall or runoff from the land. ‘‘We found that the 54 trillion litres that’s extracted from the ground in this region leads to a sealevel rise of 0.16mm. That’s roughly equivalent to the contribution to sea level rise from melting Alaskan glaciers which is around 5%. This is also the largest rate of groundwater loss in any comparable-sized region on Earth,’’ Tiwari said.
    The study combined data from GRACE (Gravity Recovery And Climate Experiment) satellite with hydrological models from 2002 to 2008 to reach their conclusions. They used gravitational field changes detected by GRACE, corresponding to gain or loss of mass, to compute the groundwater levels. The satellite is sensitive to water level changes of up to 1cm.
    Tiwari pointed out that high level of groundwater depletion should also be seen in the context of climate change models which predict increase in extreme weather event in the region. ‘‘Extreme weather events like heavy spells of rain do not recharge groundwater level. This means the region is likely to witness acute shortage of water in the foreseeable future,’’ he said. Interestingly, the study found significantly less groundwater exploitation in south India. It says, ‘‘The trends are considerably smaller than the negative trends in the north, and could be due to a combination of increased reservoir impoundment, mis-modelled naturally varying storage and (along the southeast coast) tectonic signals related to the Dec 26, 2004 Sumatran earthquake.’’