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Friday, August 21, 2009

Groundwater depletion in India

Groundwater is a primary source of fresh water in many parts of the world. Some regions are becoming overly dependent on it, consuming groundwater faster than it is naturally replenished and causing water tables to decline unremittingly, as reported in the recent findings published in Nature (see ref.).

Indirect evidence suggests that this is the case in northwest India, but there has been no regional assessment of the rate of groundwater depletion. The authors used terrestrial water storage-change observations from the NASA Gravity Recovery and Climate Experiment satellites and simulated soil-water variations from a data-integrating hydrological modelling system to show that groundwater is being depleted at the rate of 3-5 cm/year equivalent height of water (or 13.2 - 22.2 cubic km/year) over the Indian states of Rajasthan, Punjab and Haryana (including Delhi).

During the study period of August 2002 to October 2008, groundwater depletion was equivalent to a net loss of 109 cubic km of water, which is double the capacity of India's largest surface-water reservoir. Annual rainfall was close to normal throughout the period and it was demonstrated that the other terrestrial water storage components (soil moisture, surface waters, snow, glaciers and biomass) did not contribute significantly to the observed decline in total water levels.

Although the observational record is brief, the available evidence suggests that unsustainable consumption of groundwater for irrigation and other anthropogenic uses is likely to be the cause. If measures are not taken soon to ensure sustainable groundwater usage, the consequences for the 114 million residents of the region may include a reduction of agricultural output and shortages of potable water, leading to extensive socio-economic stresses.

Ref: Matthew Rodell, Isabella Velicogna & James S. Famiglietti, "Satellite-based estimates of groundwater depletion in India", Nature advance online publication 12 August 2009 | doi:10.1038/nature08238

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