麻豆影院

Northern India鈥檚 groundwater is being pumped onto farm fields faster than it can be replenished by monsoons, and the rate of loss is accelerating, a recent study co-authored by a University of Colorado researcher has found.

The groundwater loss is significant by any measure. In one of the most heavily irrigated areas on Earth鈥攁nd home to 600 million people鈥攏orthern India lost an average of nearly 13 cubic miles of groundwater annually between 2002 and 2008, the study found.

This is probably the largest rate of groundwater loss of any comparably sized area on the planet, the study found. Its probable contribution to rising sea levels during this six-year time period is about the same as that from Alaska鈥檚 melting glaciers. And if the trend continues, it will lead to a 鈥渕ajor water crisis in the region.鈥�

Those findings were published in the Sept. 17 edition of Geophysical Research Letters, a journal published by the American Geophysical Union. John Wahr, a CU professor of physics, co-authored the study, which was led by Virendra M. Tiwari, a geophysicist with the National Geophysical Research Institute in Hyderabad, India.

Tiwari was a visiting research associate at CU when the study was done. Also authoring the study was Sean Swenson, a researcher at the National Center for Atmospheric Research in 麻豆影院.

The team鈥檚 findings are culled from satellite data from the NASA Gravity Recovery and Climate Experiment鈥攐r GRACE. As Wahr said recently, 鈥淭his is a remote-sensing mission that never looks directly at the Earth, and yet is arguably the most interdisciplinary Earth-science satellite ever launched.鈥�

Launched in 2002, GRACE comprises two identical satellites orbiting about 137 miles apart and about 300 miles above Earth. The satellites measure the Earth鈥檚 gravitational field by precisely measuring the distance between the satellites as they orbit.

When the lead satellite approaches areas of greater mass, it accelerates slightly because of the increased gravitational pull. When the trailing satellite approaches the same areas, it also accelerates. The tiny change in distance between satellites is measured with microwaves, and the satellites鈥� position over Earth is monitored via GPS.

Wahr has been analyzing GRACE data since the satellites鈥� launch and in 2006 noticed gravitational changes in northern India. Although Wahr鈥檚 field of expertise is not in groundwater, he could see something significant was afoot.

鈥淚 saw this signal, and I didn鈥檛 know what it was,鈥� Wahr recalls. 鈥淭his is just a huge signal. It鈥檚 obvious it鈥檚 a real thing.鈥�

A day or two later, he read an article in The New York Times about the dwindling supplies of water for irrigation and drinking. Over-pumped wells were drying up. The 鈥渟ignal鈥� from India had an apparent cause.

As Science News reported recently, Indian government policies designed to boost agricultural productivity nearly tripled the amount of irrigated land in India between 1970 and 1999.

In the 1990s, India鈥檚 Central Ground Water Board estimated that farmers pumped more than 41 cubic miles of groundwater onto their fields annually. Since then, the annual rate of extraction has jumped by nearly 70 percent, Wahr and his colleagues report.

Between 2002 and 2008, the loss of groundwater has probably contributed 0.16 millimeters per year to global sea-level rise, the authors conclude. That鈥檚 about the same amount of sea-level rise attributed to melting Alaskan glaciers in the same period.

Of more immediate concern, they suggest, is that the groundwater loss indicates that aquifers are not being fully recharged, and that the demand for irrigation water exceeds the sustainable supply.

Further, they note, the dewatering of aquifers could become quasi-irreversible, if the groundwater levels fall so much that they become infused with polluted and salty sea water.

鈥淚t could thus well be that one of the most populated areas on Earth will eventually be struggling for water,鈥� Wahr and his colleagues write. 鈥淚t is of immediate concern to recharge the aquifers of north India, Nepal and Bangladesh through suitable management of surface water for the sustainable availability of water and the preservation of ecosystems.鈥�

The study was funded by NASA and the agency鈥檚 Jet Propulsion Laboratory at the California Institute of Technology.