New Data Show Quickening Loss of Groundwater beneath India: Increased Crop Irrigation Is Depleting Region's Aquifers

Article excerpt

Irrigation in northern India in recent decades has pulled water from the ground faster than the region's soaking monsoon rains can replenish it. And satellite data reveal that the pace of extraction has accelerated during that time, scientists report in two new studies.

In an area that is home to about 10 percent of the world's people, that could be a recipe for disaster, policy experts say. A growing population with an increasing standard of living will boost the demand for groundwater, a trend that could eventually lead to reduced agricultural yields, shortages of potable water and an increase in societal unrest.

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 at 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, previous research has found.

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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 portions of the study region in northeastern India, southern Nepal and western Bangladesh, Tiwari says. That's more than three times the capacity 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 colleagues report.

Researchers estimate that monsoon rains supply, at most, 246 cubic kilometers of precipitation to the region each year, Tiwari says. So, during the mid-1990s, groundwater supply--which largely comes from rainfall that soaks into the ground--was sufficient to meet agricultural demands. But data gathered from April 2002 to June 2008 by the Gravity Recovery and Climate Experiment's two satellites show that irrigation now extracts substantially more water than is replenished each year.

GRACE, a joint mission of NASA and DLR, the German aerospace center, is designed to map changes in Earth's gravitational field (SN: 1/4/03, p. 6). The craft can discern movements of groundwater--which, Tiwari says, often flows away from a region or evaporates after being pumped from aquifers.

Across northern India and nearby regions, including parts of Afghanistan, the net loss of groundwater averaged 54 cubic kilometers per year between 2002 and 2008, he and colleagues estimate. As a result, the water table, the upper water surface in the aquifers, fell 10 centimeters or so per year. This loss of groundwater has about the same volume as the water that melted from Alaska's glaciers during the period, he notes.

A separate analysis of GRACE data, focused on northwestern India, also reveals groundwater depletion. From August 2002 to October 2008, farmers pumped an average of 17.7 cubic kilometers of water a year from aquifers under three Indian states, says hydrologist Matthew Rodell of NASA's Goddard Space Flight Center in Greenbelt, Md. …