The groundwater storage level in the Ganges basin has been declining by 2.6 cm per year. Its effect can be clearly seen in Rajasthan, Haryana and Delhi. The average decline in storage in Uttar Pradesh, Bihar, and West Bengal was estimated to be 2 cm per year, 1 cm per year, and 0.6 cm per year, respectively.
Groundwater storage in Ganga
According to new research published in the journal Nature Scientific Reports, the aquifers in the Ganges basin are one of the largest groundwater reserves in the world.
Indu J, an associate professor at IIT-Mumbai and one of the study’s authors told Down To Earth that the Ganges basin is known for several factors, one of which is declining groundwater. “Until now, our studies have used satellite or modelling data, but when following a single approach, there are many uncertainties involved, as each has its own advantages and disadvantages,” she said.
Researchers from the Commonwealth Scientific and Industrial Research Organization (CSIRO) Land and Water, the University of Bergen and the Indian Institute of Technology Roorkee used three different methods to study long-term groundwater storage in six states.
West and South-West regions were worst hit
First, the team collected groundwater level data from the Central Ground Water Board between 1996 and 2017. The analysis found that the average groundwater level is falling at a rate of 2.6 cm per year between 1996-2017. The study showed that the West and South-West regions were worst hit, including agricultural and urban areas like Delhi and Agra.
The second method involved analysis of satellite data from the Gravity Recovery and Climate Experiment (GRACE), which recorded an average decline of 1.7 cm per year.
The team calculated the amount of water entering and leaving the aquifer storage. The difference between the two accounted for storage loss, which was approximately 3.2 cm per year. Indu J said that in all three analyses, we got the same answer: groundwater in the Ganges basin is running out.
Delhi, Haryana have highest groundwater withdrawal
Abhijit Mukherjee, a professor at IIT Kharagpur, who was not among the study authors, agreed that his team also came to similar conclusions. Delhi and Haryana have the highest groundwater withdrawal and hence a sharp decline could be observed.
According to Mukherjee, Rajasthan has shown some improvements in groundwater levels in the recent past. The state’s groundwater supplies 90% of drinking water and 60% of irrigation.
A recent annual publication by the Central Groundwater Board, which monitors groundwater levels four times a year, found that water levels in 2021-2022 have risen compared to the 2011-2020 average, except for the period pre-monsoon.
A 2019 study estimated groundwater depletion of more than 5 cubic kilometres per year in Assam, which lies under the Brahmaputra Basin.
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