While climate warming is expected to significantly increase the flow of most of India’s major rivers, the Cauvery basin stands out as an exception. According to a study by researchers at the Indian Institute of Technology (IIT), Gandhinagar, published in the peer-reviewed journal Earth’s Future, the river faces a potential “short-term decline” of around 3.5% of its waters between 2026 and 2050, even as its northern counterparts brace for floods.
Given the strained history of Cauvery water sharing between Karnataka and Tamil Nadu, particularly in years of deficit rainfall, the study suggests that despite climate models predicting increased rainfall from global warming in India in the coming decades, the Cauvery may not benefit. In such a situation, river interlinking projects like the proposed Godavari-Cauvery interlinking project may be necessary, researchers say.
The study found that the Cauvery experienced a 28% decline in flow between 1951 and 2012, based on data from Kollegal, which one of the authors told The Hindu “well represents” actual flows in the Cauvery.
Limited access to modeling
While the study is based on a modeling study and relies on extrapolation, it attempts to limit the errors that can creep in from the blind application of climate models to predict the impact of global warming on Indian rainfall. To do this, the authors use a new statistical framework and base their analysis on actual river flows between 1951 and 2012, measured at nine stations representing nine major river basins of India, and then extrapolate the data using a “constrained modeling” approach.
The nine rivers are Cauvery (measured at Kollegal), Ganga (Farakka), Brahmaputra (Bahadurabad), Indus (Bhakra), Godavari (Polavaram), Krishna (Kurundwad), Mahanadi (Basantpur), Narmada (Mandleshwar) and Tapi (Burhanpur).
Strange history
Decades of failed water-sharing negotiations between Karnataka and Tamil Nadu led to the establishment of the Cauvery Water Disputes Tribunal (CWDT) in 1990, which took 17 years to reach its final order in 2007. The tribunal calculated the total available water at 740 thousand million cubic feet (TMC) in a normal year and allocated shares accordingly. A 2018 Supreme Court verdict allocated 404.25 TMC to Tamil Nadu and 284.75 TMC to Karnataka while declaring the Cauvery a national asset.
In 2023, Tamil Nadu demanded 24,000 cusecs per day due to severe drought, but Karnataka refused, citing its own water scarcity, leading to widespread protests in both states.
Almost medium-term water shortage
The study highlights a persistent problem in climate science: while models agree that India will warm, they differ widely on exactly how much rain falls. Using observational constraints, the researchers found that only 8 of 22 models accurately captured the seasonality of the Indian monsoon.
The source models used are CMIP6 (Coupled Model Intercomparison Project Phase 6), which is the latest generation of global climate models used by scientists to project future climate change.
Unconstrained models show a 5% increase in the Cauvery in the near future, the researchers said, as well as a 25% increase in the Indus, 8% in the Ganges and 16% in the Krishna. When the projections were reduced to these “constrained” or more reliable models, the certainty of a wetter future for most rivers increased, but the outlook for the Cauvery remained bleak as the basin faced “near- and medium-term water shortages”.
Data-driven alerts
The researchers, led by Dipesh Singh Chuphal and Professor Vimal Mishra of IIT Gandhinagar, were able to reduce the projection uncertainties by almost one-third to derive their estimates. “The raw outputs have biases due to model resolution, the simplified physics used by global climate models. To correct these biases and show future trends based on what is actually observed, we use constrained models,” Mr Chuphal, lead author of the study, told The Hindu. “When it comes to the Cauvery, it means water sharing could become more difficult.
Crucially, the researchers simulated “naturalized” flows, meaning the study focused purely on changes caused by climate, without accounting for human interventions such as dam operations or irrigation. In the real world, these human pressures could potentially exacerbate the projected shortage in the Cauvery.
“Reliable information on how India’s major rivers will respond to a changing climate is critical to securing food, water and energy for around two billion people,” the study concludes, offering data-driven warnings for one of India’s most stressed regions.
Published – 25 March 2026 22:34 IST
