In the summers of 2015 and 2017, domestic water supply in the northern Indian plains was severely affected because of low water level in Ganga
Water level in River Ganga depleted at a rate of −0.5 to −38.1 cm/year between the summer of 1999 and 2013, according to a recent study published in Nature’s Scientific Reports on August 13. The study revealed that the constant reduction in water flow in downstream states was caused by groundwater depletion in the adjoining Gangetic aquifers. “Both the in-situ and remotely sensed observations suggest that the pre-monsoon Ganges river water is continuously depleting,” the study observes.
The summers of 2015 and 2017, according to the study, witnessed an unprecedented low water level and flow in the middle and lower reaches of the Ganga. Domestic water supply, irrigation water requirements, river transport and ecology of the densely populated northern Indian plains were severely affected because of low water level.
Over 120 million residents in downstream region got affected. Predictions made in the study suggest that the average groundwater contribution to the river can substantially decrease in future. “The observed summer drying in the recent years, in the studied reaches of the river, pose a much bigger crisis, possibly suggesting an impending surface water crisis in the region, in conjunction with the already well documented, ongoing ‘groundwater drought’ in the Indian subcontinent,” the authors of the study observes.
Concern over food security
Large population residing in the Indo-Gangetic basin is vulnerable, and would experience substantial reduction in food production if extraction of groundwater continues at the current unsustainable rate. The study states that surface water irrigation for cropping accounts for 27 per cent of the total irrigation in the region.
Due to constant decrease in water level, by 2050, the total carbohydrate-based food would be unavailable for almost 1/5th (approximately 115 million) of the total inhabitants in the region studied, this collaborative study predicts. This sounds ominous, especially when the report predicts that by 2050, the base flow of Ganga would decrease by 38 per cent as compared to 2016.
Climate change and the Himalayan glacial retreat make the future look catastrophic, raising question about the existence of this river that sustains (providing both water and food) the densest and largest riverine population in the world over the years.
The study recommends
Abhijit Mukherjee, lead author of the paper and associate professor (Hydrogeology) in School of Environmental Science and Engineering, Indian Institute of Technology (IIT), Kharagpur said that the study tried to address the rate of water level change over the years, the factor controlling this process, dynamics of river water-groundwater interactions, and the impact of river water depletion on food security in the region.
The study suggests a need for implementing adaptation options related to either food production or water use in agriculture: water-efficient agricultural practices (modification of existing food irrigation techniques), conversion to water-saving crops, reduced groundwater pumping, aquifer rejuvenation and managed recharge.
The results of this study could be used to understand groundwater-linked river water depletion as well as the regional water security in other densely populated regions of the world.
The study has been co-authored by Soumendra Nath Bhanja from IIT-Kharagpur, and Yoshihide Wada from Utrecht University.
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