Climate study shows drying of Cauvery to persist until 2050, even as other rivers swell

A study reveals the Cauvery River may decline by 3.5% by 2050, contrasting with increasing flows in northern rivers.

While a warming climate is expected to significantly increase the flow of most major Indian rivers, the Cauvery basin stands out as an exception. The river faces a potential “near-term decline” of approximately 3.5% of its waters between 2026 and 2050, even as its northern counterparts brace for floods, according to a study by researchers at the Indian Institute of Technology (IIT), Gandhinagar, published in the peer-reviewed journal Earth’s Future.

Given the fraught history of Cauvery water sharing between Karnataka and Tamil Nadu, particularly in years of deficit rainfall, the study suggests that despite climate models projecting increased rainfall from global warming in India in the decades ahead, the Cauvery might not benefit. In such a situation, river interlinking projects, such as the proposed Godavari-Cauvery link project, might be necessary, the researchers say.

The study finds that the Cauvery experienced a 28% decline in streamflow between 1951 and 2012, based on data from Kollegal which, one of the authors told The Hindu, “well represented” actual flows in the Cauvery.

While the study is based on a modelling study and is reliant on an extrapolation, it attempts to reduce errors that can creep in from blindly applying climate models to predict the impact of global warming on Indian rainfall. To do that, the authors use a novel 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 extrapolates the data using a ‘constrained modelling’ approach.

The nine rivers are the Cauvery (measured at Kollegal), the Ganga (Farakka), Brahmaputra (Bahadurabad), Indus (Bhakra), Godavari (Polavaram), Krishna (Kurundwad), Mahanadi (Basantpur), Narmada (Mandleshwar), and Tapi (Burhanpur).

Decades of failed negotiations on water sharing between Karnataka and Tamil Nadu led to the establishment of the Cauvery Water Disputes Tribunal (CWDT) in 1990, which took 17 years to reach a final order in 2007. The tribunal calculated total available water at 740 thousand million cubic feet (TMC) in a normal year, and allocated shares accordingly. The 2018 Supreme Court verdict allocated 404.25 TMC to Tamil Nadu and 284.75 TMC to Karnataka, while also declaring the Cauvery a national asset.