Human consumption has caused a decline of 109 cubic kilometres in the amount of groundwater beneath northern India since 2002, says a study by American researchers.
The decrease, which amounts to a one-foot fall in groundwater levels every year over the past decade, is 66 times more than Delhi’s annual water requirement of 1.65 cubic kilometres.
The findings, which appeared in Wednesday’s edition of the online journal Nature, have serious implications for agricultural production in the country, where groundwater makes up nearly half of the water used for irrigation.
Nearly 60 per cent of the nation’s food production depends on groundwater, according to the World Bank. Farmers use tube wells – crude wells that use a small motor to withdraw water from deep within the earth — to extract groundwater.
In 1994, there were 6.7 million tube wells in India. Now the number may be as high as 25 million.
“If measures are not soon taken to ensure sustainable groundwater usage, consequences for the 114 million residents of the region may include a collapse of agricultural output, severe shortages of potable water, conflict and suffering,” wrote the authors of the study.
This year’s rainfall, which at just 376.6 millimetres has been below average by 25 per cent, can result in an even greater reliance on strained groundwater reserves. The problem is especially acute in states like Delhi, which received just 243.7 millimetres, 61 per cent below the long-term average.
The scientists, based at the University of California, Irvine and the National Aeronautics and Space Administration, used a satellite monitoring system that tracks minute changes in gravity caused by the growth and shift of large bodies of water.
Beginning in 2002, for six years, they observed Haryana, Punjab, Rajasthan and Delhi. After accounting for changes in rainfall, soil moisture and glacier activity, they concluded that human pumping of groundwater resources for irrigation and personal consumption must have caused the decline.
Rapid use of groundwater is cause for concern as these underground aquifers can take thousands of years to recharge.
“Every farmer has a tube well and draws water at his own whim,” said M K Gulati, an engineer who worked with the Haryana Irrigation Department for 30 years. “It’ll come to the point where we’ll be mining water.”
Cities are also pumping more groundwater to meet domestic demand, said T H Syed, a professor of applied geology at the Indian School of Mines University, Dhanbad.
“Residents of apartment buildings where there is no proper water supply call up a local plumber and he installs a well,” Syed said.
The union water resources ministry tracks groundwater levels at 15,000 stations across India. Measurements are taken four times a year at each station using manual and digital readers.
“Groundwater is being heavily withdrawn in certain areas such as Haryana, Rajasthan, Delhi and Punjab,” said S K Sharma, a groundwater consultant with the ministry.