The Indian sub-continent’s two great northern river systems — the Indus and the Ganga — are moving in opposite hydrological directions, with important implications for water security across South Asia, according to a study published in the peer-reviewed Earth’s Future, a publication of the American Geophysical Union.
Researchers from the Indian Institute of Technology, Gandhinagar analysed changes in streamflow — or how the quantity of water in rivers, lakes, and groundwater varied — between 1980 and 2021 using a high-resolution, physics-based hydrological model that links rainfall, groundwater, river flow, and irrigation pumping. Their findings show that while overall flows in the Indus Basin have increased modestly, the Ganga Basin has experienced a sharp and sustained decline.
According to the study, annual streamflow in the Indus Basin rose by about 8% over the past four decades. In contrast, the Ganga Basin saw a 17% reduction in flow over the same period.
Stark differences
In the Indus system, rising precipitation — particularly linked to western disturbances and variable monsoon contributions — appears to be the main driver of increased river flow. The study finds that the strongest increases are seen in the main Indus River and its western tributaries, the Jhelum and the Chenab. However, the increase is not uniform: two eastern tributaries, the Ravi and Sutlej, have experienced significant declines despite the basin-wide upward trend.
In the Ganga Basin, the picture is starkly different. Rainfall has declined by roughly 10%, while temperatures and atmospheric water demand have increased. But the dominant factor behind falling river flows, the researchers concluded, is intensive groundwater pumping for irrigation.
Indus Waters Treaty implications
The research findings intersect with the 1960 Indus Waters Treaty (IWT), which allocates the eastern rivers — Ravi, Beas and Sutlej — to India, and the western rivers — Indus, Jhelum and Chenab — primarily to Pakistan. India suspended the treaty in April 2025, following the Pahalgam terror attack. It has since fast-tracked procedural clearances for hydropower projects to accelerate usage of its share of the western rivers.
Vimal Mishra, an IIT-G professor and one of the co-authors of the study, told The Hindu that these trends showed that climate change and human use of water “necessitated” a relook at water-sharing arrangements under the IWT. “Agriculture in Pakistan is largely dependent on water from the main stem of the Indus and the increased precipitation means that it is not as affected as in eastern Punjab in India where groundwater is declining,” he told The Hindu.
Depleted groundwater impact
Groundwater normally feeds rivers gradually through underground discharge, especially during dry months. The study estimates that in parts of the Ganga Basin, groundwater contributes 50% to 70% of annual river flow. When farmers pump heavily — particularly during weak monsoon years — less groundwater reaches rivers. In some stretches of the Yamuna and upper Ganga, the natural direction of flow between aquifers and rivers has even reversed, with rivers losing water to depleted groundwater systems.
Using a two-step statistical attribution framework, the authors estimate that 60% to 80% of the streamflow decline in major Ganga sub-basins such as the Yamuna, Upper Ganga, and Ramganga can be traced to groundwater extraction, including pumping triggered by rainfall deficits during drought years.
The study’s methodology relies on a surface-groundwater model known as ParFlow-CLM, run at roughly 5-kilometre resolution for 42 years. The model was then given input data such as observed rainfall, temperature, soil, land use, and irrigation. Its results were validated against available streamflow measurements, the Gravity Recovery and Climate Experiment (GRACE) satellite groundwater storage observations, and data from more than 1,500 monitoring wells, showing strong agreement in groundwater trends.
Integrated management needed
The authors call for integrated management of surface water and groundwater. Treating rivers and aquifers as separate systems, they argue, is no longer viable in an agriculture-dominated region where pumping decisions directly affect river flows. “We cannot continue to indiscriminately draw on water as if it is a free resource. Water use efficiency, changes in the types of crops grown has to be seriously considered,” added Professor Mishra.
In their study, the authors recommend more adaptive irrigation practices, crop diversification away from water-intensive crops in drought-prone years, and water planning aligned with long-term climate variability. Without coordinated groundwater regulation and climate-aware management, the study warns, river drying in the Ganga Basin is likely to intensify.
Published – February 14, 2026 07:50 pm IST
