Groundwater is invisible. When the snow melts and the rain falls, the water flows into rivers. A portion of that flow percolates down the surface and is stored as groundwater. Over the course of time, the water stored beneath the surface bubbles up into rivers. That is why we find rivers flowing even when there is no snow melt or rainfall. It’s groundwater resurfacing as streamflow.

A new paper—Drying of the Himalayan Indus-Ganges-Brahmaputra (IGB) Rivers: Understanding Causes and Management as a “One Water” Resource—published February 27 in the American Chemical Society’s ES&T Water journal, investigates the interaction between groundwater and the Himalayan rivers. When researchers Abhijit Mukherjee of IIT Kharagpur and his colleagues looked at the past 20 years of streamflows in IGB, they found flows coming down, especially at the lower parts of the rivers. Researching why this might be led them to decreasing levels of ground water in these areas.

“We found out that the groundwater in all these areas has been heavily extracted in the recent past,” says Abhijit Mukherjee, the lead author. As a result of heavy extraction, groundwater levels go down, and there remains barely enough water to reemerge into rivers.

“Rivers in the dry times, like non-monsoon times, they mostly survive due to the groundwater,” says Mukherjee.

Each of the water sources for rivers—glacial melt, rainfall and groundwater—has its own dynamics. In a climate-changed world, glaciers are melting more. Increased glacial melt reaches rivers and rivers are full of water. Even though glaciers go, rivers will have more water, at least for the present. But that’s not what researchers found.

Rainfall, especially in summer,  too has increased over the last 20 years. Mukherjee and his team’s research found summer rainwater flows have increased in the Upper Brahmaputra region. The researchers found streamflows in IGB are coming down even with increased flows of rainfall. They say both increased glacial melt and rainfall have not made any dent in the streamflows coming down.

“The only other thing that we can think about is that the groundwater is going down,” says Mukherjee.

It is possible that the with an increase in glacial melt there is water coming into the system, but because the groundwater level has gone down so low that even with enhanced water flows, streamflows in the river are down.

As Mukherjee puts it: Summer river water = glacial melt + summer rain + tributaries + groundwater. “A simple mass-balance equation.”

What do decreased flows mean for the region and people? Consider that the Indus, the  Ganga, and the Brahmaputra (IGB) are among the three largest river systems in the world; they support one billion people, approximately 15 per cent of the population.

Given the importance of IGB, what is the solution for the dwindling flows?

“The solution is a concept called One Water,” says Mukherjee.

He says people talk about river water, groundwater, and rainwater as separate entities. But “these are all in continuum, and they all come in a circle”. One Water envisages water polices to be flexible and not be a hostage to one part of the water cycle.

“We should take them (rainwater, groundwater and glacial melt) as one ensemble. And we should do the computation, this ensemble, taking everything together,” he says.

He says the purpose of having this paper published at this time is to make our administrators aware of the facts: when you are sharing the resource, you should not only share what is visible—river water—but also consider what is not visible—groundwater.

“When you are looking at the river water treaty and you are calculating the mass of the volume of water to be shared or not to be shared, it actually includes a major part of the groundwater that is invisible.” If groundwater is not taken into account in treaties, sharing of water will doom rivers.

In that sense, this is not just like a scientific study but it’s also a policy study. “Our administrators should be aware of this fact. When you are sharing the river water, it’s not just the river water that you’re sharing, you’re also sharing the groundwater along,” says Mukherjee.

More immediate implication of the study is at our doorstep. Summer is already on. Wells will go dry; river flows will reduce to a trickle.

To manage our water for summer, an overhaul of thinking is necessary.

When we are talking about water management, Mukherjee says, all the agencies do it on a unit by unit basis. For example, the Central Water Commission only looks into river water; the Central Groundwater Board looks only into groundwater; the Meteorological Department looks only into rain water.

“So, if you’re talking about management, you need to take them all as a whole number, like one number,” he says. “You should be aware that rivers are just not rivers. These are composites of the rainwater, glacial water, and the invisible groundwater.”