Drivers of contrasting changes in streamflow in the Indus and Ganga river basins

The Indus and Ganga are the two major transboundary rivers that are lifelines for millions of people and their food security in the Indian sub-continent. However, the observed changes in streamflow in these basins and their drivers remain poorly understood. Using in situ and satellite observations, and hydrological modeling, we show contrasting trends, with a ∼8% (p-value = 0.046) increase in streamflow in the Indus Basin due to rising precipitation. In contrast, a sharp decline of ∼17% (p-value = 0.008) in the Ganga Basin driven by intensive groundwater pumping during 1980–2021 and despite the overall increase in streamflow in the Indus Basin, two sub-basins, Ravi and Sutlej, faced a decline in streamflow. Three major sub-basins of the Ganga River, including Yamuna, Ramganga, and Upper Ganga, also experienced a decline in streamflow. About 60%–80% of the streamflow decline in the Ganga Basin is attributable to intensive groundwater pumping, further amplified by weakening summer monsoon precipitation. Drought-induced groundwater pumping exacerbates river drying, especially during the dry season (October–May). Our findings highlight the dominant role of coupled climate-human interactions in driving streamflow changes and emphasize the urgency of integrated surface-groundwater management to safeguard water and food security in India.