Unhappy news from new studies on India's groundwater

Two articles in scientific journals recently analyzed satellite data and came up with similiar alarming results for the depletion of India's groundwater in the Indo-Gangetic basin:

http://sciencenow.sciencemag.org/cgi/content/full/2009/810/1 is an article based on a research paper in the Geophysical Research Letters by a team including geophysicist Virendra Tiwari of National Geophysical Research Institute.

And IEEE Spectrum talks about a paper in Nature that covers the same ground:
http://www.spectrum.ieee.org/aerospace/satellites/satellites-peer-into-indias


Quoting from Richard Kerr's article in the Science Mag link above:

"The big picture of Indian groundwater comes from the Gravity Recovery and Climate Experiment (GRACE) satellite mission, launched in March 2002 as a joint effort by the U.S. National Aeronautics and Space Administration and the German Aerospace Center. Actually two satellites orbiting in tandem 220 kilometers apart, GRACE measures subtle variations in the pull of Earth's gravity by using microwaves to precisely gauge the changing distance between the two spacecraft.
As the lead spacecraft passes over a patch of anomalously strong gravity, it accelerates ahead of the trailing spacecraft. Once past the anomaly, the lead satellite slows back down. Then the trailing spacecraft accelerates and again closes on the leader. By making repeated passes over the same spot, GRACE measures changes in Earth's gravity, which are mainly due to water moving on and under the surface. ..
Outside of wasting ice sheets, the world's largest broad-scale decline in gravity during GRACE's first 6 years came across a 2.7-million-square-kilometer, east-west swath centered on New Delhi. That's according to a study in press in Geophysical Research Letters by geophysicists Virendra Tiwari of the National Geophysical Research Institute in Hyderabad, India; John Wahr of the University of Colorado, Boulder; and Sean Swenson of the National Center for Atmospheric Research in Boulder. Adjusted for natural variations due to changing precipitation and evaporation, the decline in gravity that GRACE determined equates to a net loss of 54 plus or minus 9 cubic kilometers of groundwater per year, the group reports. That would produce a fall in the water table of about 10 centimeters per year averaged over the entire region.
A falling water table across the northern Indian subcontinent comes as no great surprise. The GRACE region of sharp groundwater depletion coincides with the world's most intensely irrigated land: Fifty percent to more than 75% of the land is equipped for irrigation with pumped groundwater or reservoir water. And then there are those 600 million people drawing heavily on groundwater. But, the group calculates, the GRACE-determined depletion rate implies that groundwater was being pumped out 70% faster in this decade than the Central Ground Water Board of India estimated it was in the mid-1990s. The apparent surge in withdrawal would have been large enough to turn a once-stable water table into a falling one that demands ever-deeper wells and bigger pumps and may draw in salty or polluted water."

Questions that come to mind:
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** How reliable are these results? This is pretty much the first attempt to deduce groundwater status information from gravity change data. How are the results to be seen in this situation ?
** We already knew that groundwater depletion was a big problem. Is this study corraborative or conflicting with other sources of information ? For eg. the article above says that the rate of groundwater extraction is 70% more than CGWB's estimates for the mid-90s ? Can someone explicate on this ?
** Groundwater depletion was also seen as a big problem in peninsular India, whereas these results say the problem is worst in N.India
** If anyone can forward hard or softcopies of the orignal articles to the Water Portal, these can be made available to the wider public.

A note from Himanshu Thakkar of SANDRP on the above can be seen at:
http://www.indiawaterportal.org/blog/2009/08/17/alarm-bell-on-groundwater-its-not-bottomless/

We request all who are competent in the above areas to comment !