Runoff variations and governing factors in transboundary basins through multisource data and water budget during 2003–2021

ABSTRACT Quantifying the spatiotemporal variability in the Runoff Coefficient (RC) is crucial for ensuring sustainable management of water resources in transboundary river basins. Here, we quantify RC variations across the Ganga, Indus, and Brahmaputra River Basins, from a water budget perspective over the past two decades. To reduce uncertainties implicit in individual datasets, the ensemble mean approach is employed, leveraging multi-source datasets of precipitation, runoff, evapotranspiration, and changes in terrestrial water storage from satellite data, in-situ measurements, reanalysis, and hydrological simulations. Furthermore, we analyse contributions of Evapotranspiration Coefficient (EC) and Storage Coefficient (SC) to RC variability. Our results reveal that the Brahmaputra Basin exhibits the highest average annual RC of 0.71, followed by the Ganga (0.41) and Indus (0.40) Basins. Brahmaputra and Ganga have increasing RC trends, while Indus has a slightly declining RC trend. The Ganga Basin shows a mean EC (and SC) of 0.57 (−0.01), the Indus has 0.70 (−0.02), and the Brahmaputra has 0.35 (−0.01). All three basins reveal divergent trends in EC and SC, highlighting the relative contributions of ET and storage to R. These findings underscore the importance of continuous monitoring of R dynamics over transboundary river basins for informing sustainable water resource management strategies.