However the recent GRACE (Gravity Recovery And Climate Experiment) mission report released in the Nature journal on August 12th by the UC Irvine and NASA hydrologists, are of immediate concern. The findings conclude that groundwater beneath Northern India (Rajasthan, Punjab and Haryana, including Delhi) has been receding by as much as 1 foot (33 cms) every year over the past decade. Using terrestrial water-storage-change observations from the two satellites and simulated soil-water variations from a data-integrating hydrological modelling system, the findings conclude that groundwater is being consumed faster than is being naturally replenished, causing water tables to decline unremittingly in this region.
According to Science Daily,
The map shows changes in India during 2002-08, with losses in red and gains in blue, based on Grace satellite observations. The estimated rate of depletion of groundwater in north-western India is 4 cm of water / year, equivalent to a water table decline of 33 cms / year. Increases in groundwater in southern India are due to recent above-average rainfall, whereas rain in northwestern India was close to normal during the study period.
The GRACE satellites are a pair of roving satellites that sense changes in the Earth’s gravity field and associated mass distribution, including water masses stored above or below the Earth’s surface. As the satellites orbit 483 kms above Earth’s surface, their positions change relative to each other in response to variations in gravitational pull. Minute changes in data are extrapolated to show the water distribution patterns.
As evidences all over the world indicate increasing groundwater depletion and changes in water supplies, the NASA sponsored GRACE is mapping groundwater supplies in regions like the central valley of California, central U.S., parts of India and the Nubian valley in Africa. With its water tracking mission, GRACE now plans to send new map data every 30 days that will give a time-variable view of the gravity profile.
The hydrological findings of GRACE pertaining to north-western India comes in the wake of another study by V. M. Tiwari, J. Wahr and S. Swenson, that attempts to show fast depleting groundwater supplies in these parts of India.
Northern India and the surrounding areas — a 2,000-kilometer-long swath that rims the Himalayas from Pakistan to Bangladesh — are home to more than 600 million people. The region is also one of the most heavily irrigated areas in the world, says Virendra M. Tiwari, a geophysicist with the National Geophysical Research Institute in Hyderabad, India, and coauthor of a new report to appear in an upcoming Geophysical Research Letters.
Government policies put in place in the 1960s to boost agricultural productivity nearly tripled the amount of irrigated acreage in India between 1970 and 1999. In the mid-1990s, India’s Central Ground Water Board estimated that farmers pulled more than 172 cubic kilometers of water each year from aquifers in the study region of northeastern India, southern Nepal and western Bangladesh, says Tiwari. That’s more than three times the volume of India’s largest surface reservoir. New data gleaned from gravity-measuring satellites suggest that the annual rate of extraction in that region has jumped more than 60 percent since then, Tiwari and his colleagues report.
[Source : Science news]
Though regional rate of depletion has hitherto not been mapped in detail by the Indian Ministry of Water Resources, an apt observation by Himanshu Thakkar in India Water Portal needs to be analysed in the context of the actualities of the data as presented in Science Now. As observed by Mr. Thakkar, the estimates are indeed ’exaggerated statements’ and require qualification. The hydrological picture presented in these maps are also anomalous and need to be analysed by experts in the Indian context.
Nevertheless it remains that north-western India is heavily irrigated and the vagaries of monsoon are acutely felt in this historically arid region, the reason WHY this region is being drained faster than is naturally replenished, a trend that is of grave concern.
Hydrologist Matt Rodell of this GRACE mission said,
"We don’t know the absolute volume of water in the northern Indian aquifers, but GRACE provides strong evidence that current rates of water extraction are not sustainable”.
In a paper published in Current Science on June 25th, Rana Chatterjee and Raja Ram Purohit, hydrologists at Central Ground Water Board, India, have already reported groundwater overexploitation in not just north-western and western India, but also peninsular India.
According to Dr. Raj Gupta, scientist with International Maize and Wheat Improvement Centre (CIMMYT),
"Farmers have to irrigate and that’s why they are pumping more water, mining more water”.
Mounting pressure on food supplies, unpredictable monsoons and an increased frequency and intensity in drought, calls for an urgent shift in water usage regulations, irrigation reforms and government policies.