Changes in precipitation, which are linked to the warming of the Indian Ocean, is the main reason for recent decline in groundwater storage in India, a new study led by researchers of IIT Gandhinagar has warned. Agriculture in India relies heavily on groundwater for irrigation, particularly in the dry northern regions where precipitation is scarce.

Groundwater withdrawals in the country have increased over tenfold since the 1950's, from 10-20 cubic kilometres per year in 1950, to 240-260 cubic kilometres per year in 2009. Satellite measurements have shown major declines in groundwater storage in some parts of the country, particularly in northern India.

"Groundwater plays a vital role in food and water security in India. Sustainable use of groundwater resources for irrigation is the key for future food grain production," said study leader Vimal Mishra from Indian Institute of Technology (IIT) Gandhinagar.
"With a fast-growing population, managing groundwater sustainably is going become even more important," said Mishra. "The linkage between monsoon rainfall and groundwater can suggest ways to enhance groundwater recharge in India and especially in the regions where rainfall has been declining, such as the Indo-Gangetic Plain," Mishra added.

Groundwater acts like a bank for water storage, receiving deposits from surface water and precipitation and withdrawals as people pump out water for drinking, industry and irrigating fields. If withdrawals add up to more than the deposits, eventually the accounts could run dry, which could have disastrous consequences.

"This study adds another dimension to the existing water management framework. We need to consider not just the withdrawals, but also the deposits in the system," said Yoshihide Wada, deputy director of the Water program at the International Institute for Applied Systems Analysis (IIASA) in Austria. The issue of groundwater depletion has been a topic of much discussion in India, but most planning has focused on pumping or the demand side, rather than the deposit side.

By looking at water levels in wells around the country, the researchers could track groundwater replenishment following the monsoons. They found that in fact, variability in the monsoons is the key factor driving the changing groundwater storage levels across the country, even as withdrawals increase.

In addition, the researchers found that the monsoon precipitation is correlated with Indian Ocean temperature, a finding which could potentially help to improve precipitation forecasts and aid in water resource planning. "Weather is uncertain by nature and the impacts of climate change are extremely difficult to predict at a regional level," said Wada. The study was published in the journal Nature Geoscience. 
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