Since the 1960s, India’s groundwater irrigation has increased dramatically, playing an important role in its economy and people’s lives — supporting livelihoods of over 26 crore farmers and agricultural labourers who grow over a third of India’s foodgrains. These benefits, however, have come at the cost of increased pressure on groundwater reserves.

India is the world’s largest user of groundwater and, since the 1980s, its groundwater levels have been dropping. The severity of the problem is particularly acute in the northwest, where levels have plunged from 8m below ground to 16m, so that water needs to be pumped from even greater depths. Worse yet, much of this is non-renewable since recharge rates are less than extraction rates and replenishing this resource can take thousands of years.

Using up such “fossil” groundwater is unsustainable. Moreover, the future of monsoon rainfall remains uncertain; while some climate models predict an increase, others forecast a weakening monsoon, although changes in monsoon variability are already underway and will continue into the future. Historical records show the number of dry spells and the intensity of wet spells have risen over the past 50 years. As climate change alters the monsoon, the large stresses on India’s groundwater resources may increase.

Groundwater stress is more than just a hydrologic issue, as usage of the resource is shaped by human behaviour and economic policy. Diverting water to drier areas, for example, can encourage demand for water-intensive crops and further expand irrigation — leading to more stress on the physical system, the environment, and the people it supports.

Understanding how and why people use water, therefore, is an important priority. Given the complex dynamics of both human agricultural and economic decisions, not to mention physical water and crop systems, what will India’s groundwater future look like?

To answer this question, I took part in an integrated economic-hydrology assessment of non-renewable groundwater use in rural India (along with colleagues from the University of New Hampshire and Pennsylvania State University). Importantly, an integrated approach can shed light on the role that adaptation responses and policy measures can play going forward.

One such initiative proposed by the Government is to physically transfer 178 billion cubic metres of water across river basin boundaries each year by building 12,500 km of water conveyance networks. This “national river linking project” — the largest of its kind in the world — aims to expand irrigated agriculture by moving water from “water surplus” to “water deficit” basins. The first of the planned canals linking the Kaveri and Godavari rivers was completed on September 16, 2015.

Using our modelling framework, we were able to evaluate the efficacy of this proposed infrastructure on alleviating groundwater stress. We first used detailed crop and weather data since 1970 to quantify how, in response to historical monsoon variability, farmers altered the dry- and wet-season irrigated areas of six primary crops grown in India.

Assuming these responses to monsoon variability continued into the future, we projected future changes in irrigated crop areas based on a suite of monsoon rainfall projections and inputed these into a hydrological model. We were then able to model the demand for irrigation water and assess how much of this demand would have to come from sustainable irrigation supplied by groundwater recharge and surface water vs. unsustainable or non-renewable groundwater.

The analyses (published in Environmental Research Letters) reveal that even in some areas that experience projected increases in monsoon rainfall, the expansion of irrigated agriculture will lead to more non-renewable groundwater extractions. This means groundwater levels will continue to drop over the next 30 years in these areas. In extreme cases, a complete loss of non-renewable groundwater irrigation can reduce national annual crop production by as much as 25 per cent.

Our results also point to the large variation in future groundwater levels across India. Under future climate change, notably, some districts will do better and may even be able to rely solely on sustainable water supplies allowing groundwater levels to recover. Others will see slower rates of groundwater decline and yet others will experience declines for the first time. But most of Punjab and Haryana, northern areas of Rajasthan and Gujarat, and parts of Uttar Pradesh and Tamil Nadu will face continued groundwater level declines. As the levels become deeper, rising pumping costs can make extraction prohibitive and directly impact welfare.

Previous research (Sekhri, 2014) has shown that poverty is higher in places where falling groundwater reserves necessitate the use of expensive pumps. Other research (Fishman, Jain and Kishore, 2015) has demonstrated that in regions where wells have run dry, well-off farmers adapt by migrating to cities, but the poor fare worse.

This brings us back to the policy proposal: could a $120-billion river-linking project help? Our model suggests that it all depends on how this project is carried out. The project has the potential to alleviate 12-24 per cent of mid-century (2040-2050) non-renewable groundwater demand, depending on the climate model used, although the impact varies substantially across India.

But in simulations without new large reservoirs along canals, water transfers alone will alleviate very little non-renewable groundwater demand; without storage, water transfers in the wet season will not be available for dry-season irrigation. Historically, constructions of large water-holding dams and reservoirs have been contentious in India. While the exact plans for dam construction under the river-linking project have not yet been made public, it is clear that without a large increase in reservoir capacity, the proposed project will not alleviate groundwater stress.

There may be more cost-effective and sustainable ways to alleviate groundwater demand, such as more efficient irrigation, growing less water-intensive crops in the dry season and transitioning away from irrigation-intensive systems where there is little water.

In addition, India needs better policies that directly help small-holders and labourers to adapt and adjust to risks associated with groundwater depletion and a more variable future climate. A recent report submitted by a committee led by Mihir Shah titled ‘A 21st Century Institutional Architecture for India’s Water Reforms’ is a clarion call for a paradigm shift in water resource management. This is no small task. But for a resource that will shape the course of India’s economic, social, and political future, we would do well to heed Victor Hugo’s adage: “All the forces in the world are not so powerful as an idea whose time has come.”

The writer is a postdoctoral research fellow at the Center on Food Security and the Environment and Department of Earth System Science at Stanford University. This article is by special arrangement with the Center for the Advanced Study of India, University of Pennsylvania.