Estimation of glacier-stored freshwater volume present in major tributaries of the Brahmaputra basin

Estimation of the glacier-stored freshwater is important to understand the water security in the Himalayan region. While previous work has studied the western and central Himalayan glaciers, the eastern counterpart received less and more scattered attention. In this study, an attempt is made to quantify the total glacier-stored freshwater in the Brahmaputra basin and later compared with previous global models. Using open-source tools such as COSI-Corr and the Himalayan Glacier Thickness Mapper (HIGTHIM), the surface velocity and thickness of 1075 glaciers (> 1 km²) in the Brahmaputra basin were estimated, resulting in a current ice-volume estimate of 283 × 10⁹ m³. Based on the laminar flow model, the mean ice volume ranges from 8284 to 230,186 m³, with an average of 36,570 m³. Sub-basin-wise evaluations of the total glacier-stored freshwater availability in the basin were also conducted, revealing that the Siang (89.998 × 10⁹ m³, 31.45%) and Lohit (84.371 × 10⁹ m³, 29.49%) sub-basins have significantly larger ice volumes than others. The average mean ice volume for each sub-basin are as follows: Teesta (45,233 m³), Sankosh (45,552 m³), Manas (39,581.7 m³), Subansiri (40,922.4 m³), Kameng (41,241.2 m³), Siang (36,120.5 m³), Dibang (31,792.2 m³), and Lohit (30,340.6 m³). Teesta, Sankosh, and Manas exhibit relatively higher average mean ice volumes than others. In comparison with the global studies, the present study's findings are acceptable with ensemble ice-volume estimates considering an uncertainty of ± 17.35%. Therefore, these results serve as a primary input for assessing the future changes in water resources and hazards related to water in the Brahmaputra basin.