For four decades now, India has put its weight behind river interlinking projects that transfer excess water from one river basin to the other — a $168 billion answer to a swelling water stress crisis. Prime Minister Narendra Modi in 2020 said projects like the Ken-Betwa link have “huge potential to change the fate” of the regions they touch; other ministers called them a ‘permanent’ solution to droughts.
A new study published in Nature Communications, however, challenges these claims: many hydro-linking projects in India and globally are altering monsoon cycles, disturbing complex hydro-meteorological systems, which in turn “may worsen the water stress across the country, making the interlinking projects ineffective or possibly even counterproductive,” it says.
The logic behind inter-basin water transfers tracks with mathematical concepts of surplus and deficit: excess water is routed from “donor river basins” (for instance, from the Godavari river in Telangana) to “recipient” dry regions (Grand Anicut dam on Cauvery); if a maximum of water is kept on land, and does not flow into the Arabian Sea or Bay of Bengal, India’s growing water demand could be met. The presupposition is that river basins operate in silos without affecting the land or the atmosphere, but “here, we find that the assumptions made for the interlinking are not valid,” the study stated.
The team , which included researchers from the Indian Institute of Technology, Bombay and the Indian Institute of Tropical Meteorology, Pune, analysed major river basins— namely Ganga, Godavari, Mahanadi, Krishna, Cauvery and Narmada-Tapi— between 1991 and 2012, observing the summer rainfall patterns between May and October each year. They used climate regional models, reanalysis datasets and delineation techniques to see how inter-basin water transfers impact the water cycle and different atmospheric variables, such as the El Niño-Southern Oscillation, which controls soil moisture across basins.
The researchers found that surplus irrigation due to interlinking basins modified spatial patterns of summer monsoons, and was responsible for a 12% decrease in mean rainfall in September across dry arid regions that were already experiencing water stress.
The findingsdebunked the idea that river basins act as independent entities; they are connected to one another through feedback loops between the land and atmosphere, links that are formed when water evaporates from one basin or when winds transport water across basins. The study showed that since land-atmosphere feedback connects basins, changes in water levels in one can travel to neighbouring basins, altering the moisture content of the air and patterns of wind. “They impact summer monsoons and create a feedback loop, impacting water availability and climate patterns,” the study stated. Thus, over time, moisture from the Ganga basin might play a role in how clouds are formed across Chhattisgarh and Odisha around the Mahanadi basin.
The impact on ecosystems stretched beyond monsoons. Excess irrigation (using transferred water) caused soil moisture to dry up, which corresponded with a decline in rainfall and increased temperatures across the entire central Indian belt (from Rajasthan to east coast), more visible during the La Niña years (which last between one to three years).
“The hydrological processes across river basins are not independent, a critical result that most large-scale hydrological projects across the globe, including river-linking projects in India, do not consider while planning,” the study noted.
India is among the most water-stressed countries in the world, as climate change increases the frequency of floods and droughts, groundwater quality and levels decline, and urbanisation and encroachment ail water body health. The current per capita availability of water in India is around 1400 cubic meters, slated to reduce to about 1200 cubic meters by 2050, according to the Central Water Commission. The mean rainfall from the summer monsoon, which accounts for almost 80% of the annual showers, has steadily declined, while erratic rainfalls have dominated, worsening India’s floods, droughts and water stress.
The National Perspective Plan (NPP) for inter-basin transfer has identified 16 links under the peninsular rivers component and 14 links under the Himalayan component, charged with transporting 174 billion cubic metres of water each year using some 15,000 km of canals and 3,000 reservoirs. Per the Plan, these could increase the irrigated areas across the country by 30 million hectares; benefits would also pour in the form of 34,000 MW of hydropower generation, employment generation, salinity control, and pollution abatement, among other aspects.
However, the study questions the merit of these claims, arguing that reduced precipitation “can dry rivers post-monsoon, augmenting water stress across the country and rendering interlinking dysfunctional.” Activists and environmental experts have advocated for policymakers to evaluate the impact — how groundwater, land-atmosphere feedback, local ecosystems, monsoon patterns respond to inter-basin water transfers or other projects that alter the natural flow of rivers.
A 2017 paper warned that “moving even slightly away from the natural flow regime (the recorded historical pattern of floods and droughts) can lead to a collapse in the structure of ecological networks.” At the start of the decade, around 2011, researchers also found any interlinking project could cause lasting changes in the aquatic system and fish diversity.
Inter-basin water transfers, touted to be resilient solutions, present conflicting, dual objectives: of meeting water demands and balancing ecological sustainability. The present study finds it of “utmost importance” to understand complex hydro-meteorological systems when planning and implementing infrastructure projects and to “carefully consider the potential consequences of river interlinking on the nation’s water security and climate resilience”.
