In the last three decades, the groundwater input to the Ganges River in India has declined by 50 percent during the summer, a new study has found, leading to the river losing water during those dry months.

The dwindling of the river’s water flow could severely affect the availability of water for surface water irrigation, with potential declines in food production in the future.

The low river flows could also prevent effective dilution of pollutants in the Ganges, which is already one of the most contaminated transboundary rivers in the world, the researchers say.

Millions of people living in the lower reaches of the Ganges basin in India may face food shortages in the next three decades if the iconic river continues to lose water due to factors including unsustainable groundwater extraction, according to a new study.

The low river flows could also have implications for achieving United Nations’ Sustainable Development Goals (SDGs) targets, the researchers say in the study published in Scientific Reports.

The study, which analyzed the section of the Ganges (known locally as the Ganga) that runs between the city of Varanasi in the state of Uttar Pradesh and the Bay of Bengal, forecasts that in the absence of interventions, groundwater contribution to the river’s water flow will continue to diminish in the summer for the next 30 years.

“The impacts of groundwater depletion on Ganga river flows are very complex,” study co-author Yoshihide Wada, deputy director of the WAT water program at the International Institute for Applied Systems Analysis (IIASA) in Austria, told Mongabay-India. “However, our study found that there is significant concern that ongoing groundwater pumping over the basin is unsustainable, leading to not only lowering groundwater levels but also reduction in river flows during summer time.”

The problem is more serious downstream of the Ganges, Wada said.

“So far, in the last three decades we have seen the groundwater input to the river decline by 50 percent during summer,” said study lead author Abhijit Mukherjee, associate professor at the Indian Institute of Technology Kharagpur. “This decline could go up to 75 percent compared to the scenario in the 1970s in the summer months.”

The study’s model doesn’t factor in impacts of climate change. However, the authors say that if they were to do so, the situation could be worse than what is currently predicted.

The river’s 2,525-kilometer (1,569-mile) course is sustained by rainfall in the hinterlands of the Ganges basin, Himalayan glacial melt, as well as groundwater discharge. In summer or the non-monsoon months, the contribution of groundwater to the river (or base flow) can be 30 percent in some sections and can even swell up to 60 to 70 percent, Mukherjee said.

“The combination of groundwater (around 70 percent) and river water (30 percent) availability actually runs the farming system that yields the food crops,” he added.

The researchers assess that, at present, surface water irrigation for cropping accounts for 27 percent of the total irrigation in the study area. This means the dwindling of the Ganges’s flow would also severely affect the water available for surface water irrigation, with a potential decline in food production in the future.

“Our prediction shows that about 115 million people can be impacted due to insufficient food availability in the next few decades,” Mukherjee said. “In a status-quo scenario, this reduction would enhance in the future and there is a possibility that there would be reverse flow of the river water to groundwater. This is called stream flow capture.”

A ‘tragedy’

The waste of surface and groundwater is the real “tragedy,” said Upmanu Lall, director of the Columbia Water Center at Columbia University, U.S., who was not associated with the study.

“The irrigation water is not translating into the kind of yield gains we see in other states, due to a lack of agricultural extension and institution of better practices,” Lall said. “The crop yields are actually quite low and less than 50 percent of the yields for rice and wheat in the top producing Indian states.”

In effect, if large quantities of water are being withdrawn and this does not translate into the expected doubling of crop yield, then the tragedy is that the water is really being wasted.

“It is quite possible that upstream diversions contribute significantly to reduced groundwater recharge during the monsoon and hence to groundwater depletion and to base flow reduction outside the monsoon season,” Lall said.

A.K. Gosain, a professor at the Indian Institute of Technology Delhi, said that “unabated long-term groundwater extraction within the Ganga river basin has induced a sharp decrease in critical dry weather base flow contributions.”

“Despite the fact that a lot of recharge is taking place, the withdrawal is more than the replenishment (naturally from the precipitation),” Gosain told Mongabay-India. “We are mining some of the groundwater and effectively the groundwater table is falling through the years.”

Gosain said the major factor for this non-sustainability was agriculture and its inefficiency.

“Right now efficiency of agriculture is 35 percent,” he said. “Around 80 to 85 percent of the water is being used in this sector. Ganga has a lot of water. If you can increase the efficiency from 30 to 60 percent you have almost double the water availability. All other factors (domestic, industrial) are minor. If we really want to do something useful for the system you have to hit this factor.”

The lack of maintenance and control of canals, and free water provision, also leads to unreliable supply through canals, and this motivates the increase in groundwater pumping for irrigation, Lall said.

“The groundwater pumping allows access to reliable supply, and coupled with solar energy which many governments in the region are promoting, to unlimited supply in the mind of the user,” Lall said. “So, what is obvious is that the transition from surface to groundwater irrigation is now substantial.”

If crop yields were to double or triple in this region due to better agricultural methods, then total national food grain production would increase substantially, he added. This would reduce the pressure on the arid northwest and the south of the country to produce the rice and wheat for the government-run subsidized food network, the Public Distribution System (more than 60 percent comes from those regions), and avert the long-term groundwater disaster in that highly productive belt, relative to this region.

Removal of pollutants affected

The researchers say the low river flows could also influence levels of water pollution in the Ganges, already one of most contaminated transboundary rivers in the world.

“The lower the river flow, the more concentrated the pollutants become, making it difficult to wash them out,” Mukherjee said.

Wada said this was a “huge concern” for regional water supply and sanitation, and the issue could have implications for achieving the SDG targets.

“South Asian countries are working towards the United Nations Sustainable Development Goals … which aim towards improving water sanitation and reducing water scarcity, but decreasing summer river flows and increasing groundwater depletion will make only more difficult for regional policymakers to achieve the targets by 2030,” he said.

Wada called for greater cooperation between India and Bangladesh, through which the Ganges flows before emptying out into the Bay of Bengal, on regional water resources allocation.

“Local excessive groundwater pumping over two countries is affecting the river flows of the entire basin,” he said. “Regional policymakers from the two countries can cooperate for better monitoring and regulation of groundwater pumping and water use at larger.”

Wada said it was vital to understand that both upstream and downstream regions needed to share the burden of better water allocation policies. “Two countries need to work very closely to establish how to improve the situation. Water scarcity will get only worse under climate change, if the situation continues,” he said.

Rationing groundwater extraction

Since the Ganges is a transboundary river, the water levels and discharge rates are geopolitically sensitive and mostly not available in the public domain.

Notwithstanding this lack of information, the study “for the first time demonstrates quantitatively” the dependence of present-day summer drying of the Ganges on the groundwater depletion in the Gangetic aquifers of north India because of extensive groundwater pumping.

To arrive at the forecast, the team crunched satellite data, tapped into in-situ measurements of Ganges River water and groundwater levels, and ran modeling and chemical analyses.

“Generally none of the hydrological budgeting by the various government and non-government agencies account for this base flow and hence [it] pretty much stays as an invisible factor,” Mukherjee said. “Any direct measurement or report on these groundwater inputs is difficult.”

He said that as a short-term measure, groundwater abstraction should be rationed.

“Growing water-intensive crops such as paddy in rotation with crops that do not require much of water is one way of achieving this,” Mukherjee added. “For the long term, in-depth studies on groundwater-Ganga interaction at each segment of the river are needed in addition to augmentation by better governance.”

Gosain called for regulations on judicious groundwater use to strike a balance between demand and availability.

“This means you need to pinpoint what kind of crops you can grow, how much water you can withdraw, all those things and you have to also look at livelihoods,” he said. “If you look at all those procedures, your livelihood is not affected but wastage of water is minimized.”

For example, a farmer might be growing a crop that requires a lot of water. Without sufficiently large quantities of water, the farmer cannot keep on growing that crop and withdrawing the difference from the ground.

“When the water is not available to the farmer, they start digging tube wells and extract[ing] the groundwater,” Gosain said. “So the groundwater table is falling and it is more and more expensive to draw this water. And this is one of the reasons why the farmers [take out] bank loans. By the time he sows, the groundwater table has already gone down, due to collective withdrawal. So the poor fellow is not able to use that water and so there is sort of a competition between farmers. That is creating a lot of problems.”

Given the surge in demand for dry-season irrigation water for agriculture in the area, numerical models can be a useful tool to generate not only an understanding of the underlying groundwater systems but also facilitate the development of basin-wide detailed impact scenarios as inputs for management and policy actions.

“The mechanisms have to be formulated and formed and guidelines have to be made and governance has to be done in terms of water utilization,” Gosain said. “This is very doable. All the 11 states of the [Ganges] basin have to brainstorm together. You can look at each state individually but they can’t do anything that hampers the interest of [all] the states. We have the Ganga Basin Authority but we can make it more effective. There has to be political will and the society at large needs to understand this problem.”

This story was first published on Sep. 13, 2018, by Mongabay-India.

Citation

Mukherjee, A., Bhanja, S. N., & Wada, Y. (2018). Groundwater depletion causing reduction of baseflow triggering Ganges river summer drying. Scientific reports, 8(1), 12049.