River interlinking projects may change monsoon rainfall pattern: Study

Researchers from the Department of Civil Engineering and Interdisciplinary Programme in Climate Studies, Indian Institute of Technology (IIT), Bombay; in collaboration with the Indian Institute of Tropical Meteorology, Pune worked on the report

PUNE: The proposed ‘Inter Basin Water Transfer’ or ‘river interlinking’ projects may change the spatial pattern of monsoon rainfall, reveals a recent study. The study highlights that rainfall in September will be the most affected as it depends on surface moisture. Scientists participating in the study stress on the need for a comprehensive atmospheric study before implementing river interlinking projects.

The researchers analysed major river basins of the country namely Ganga, Godavari, Mahanadi, Krishna, Cauvery and Narmada-Tapi. (HT PHOTO)

Researchers from the Department of Civil Engineering and Interdisciplinary Programme in Climate Studies, Indian Institute of Technology (IIT), Bombay; in collaboration with the Indian Institute of Tropical Meteorology, Pune; and the University of Hyderabad; studied the atmospheric impact of river interlinking projects. Led by professor Subimal Ghosh and Tejasvi Chauhan, Ph.D. student, IIT Bombay, the study was published in the ‘Nature Journal’ on September 24.

The researchers analysed major river basins of the country namely Ganga, Godavari, Mahanadi, Krishna, Cauvery and Narmada-Tapi. They used multiple methods to show that these river basins are linked. As water evaporates from a basin or when it rains in a basin, land is linked to the atmosphere. Across basins, as the winds transport water, atmospheric links are formed.

The researchers found that large-scale irrigation from river interlinking projects can change the spatial patterns of the Indian monsoon. They simulated the irrigation targets of the river interlinking projects, and simultaneously observed an up to 12% reduction in September rainfall in some arid regions of the country and a 10% increase in September rainfall in other regions. The researchers stressed that changes in the spatial patterns of the monsoon must be considered while planning for the proposed river interlinking projects.

Subimal Ghosh, convenor (head) of the Interdisciplinary Programme in Climate Studies, IIT Bombay and co-author of the study, said, “This study demonstrates that altering the terrestrial water cycle can impact atmospheric processes. Hence, while planning for large-scale hydrological projects like river interlinking, there is an urgent need to include rigorous, model-guided evaluation of hydro-meteorological consequences. While there is no denying that these projects have the potential to mitigate the water crisis of our agriculture-dominant country, such projects need a holistic evaluation and subsequent planning incorporating the land-atmosphere feedback, ecological impact, groundwater interaction, oceanic changes, etc. for efficient and sustainable water resources management.”

Back in 2019, a study titled “Reassessment of Water Availability in India using Space Inputs” carried out by the Central Water Commission, Government of India, found that per capita water availability was decreasing with each passing decade. It was 1,545 cubic metres in 2011; which fell to around 1,400 cubic metres in 2021; and was slated to decrease further. With global warming and increase in population, the demand for irrigation to maintain or increase the agricultural output was rising. In addition, global warming and climate change had increased the frequency and intensity of extreme rainfall in India, which further reduced our ability to store sufficient water using current water resources’ infrastructure to meet the rising demand.

The river interlinking projects were proposed as a solution to this problem, wherein major river basins of the country would be linked using a network of around 15,000 km of canals and around 3,000 reservoirs that would transport 174 billion cubic metres of water each year. These projects presented a state-of-the-art engineering solution to India’s water crisis. The target of these projects was to increase the irrigated area across the country by 30 million hectares, out of which 20 million hectares fell within regions fed by the Himalayan rivers and 10 million hectares fell within regions fed by the peninsular rivers. In addition, these projects would generate hydropower of around 34 million kilowatts, along with benefits such as flood control, drought mitigation, and navigation. With the implementation of these projects, India was expected to shift towards an integrated, multi-reservoir operation to keep the maximum water on land which currently flows into the Arabian Sea or Bay of Bengal. However, the planning of these projects considered river basins as independent hydrological units with no existing atmospheric connections.

The latest study busts this myth, and shows that irrigation feeds moisture to the Indian monsoon in its latter stages in August and September through land-atmosphere feedback. Evapotranspiration from land contributes moisture to the air, which then gets precipitated as rainfall called ‘recycled precipitation’. Recycled precipitation contributes to nearly 25% of the monsoon rainfall in September. This means that the river basins may already be linked to each other through atmospheric pathways.