Assessing the Hydrological Controls on Spatio-Temporal Patterns of Streamwater in Glacierized Mountainous Upper Indus River Basin (UIRB), Western Himalayas

The meltwater generated from the Himalayan mountain system is an important source of freshwater sustaining hydrological, ecological and biological activities in upstream and downstream regions. Under a warming climate, the cryospheric cover is shrinking, altering the availability of freshwater to-53 million people living in the upper and lower parts of the Himalayas. Therefore, it becomes essential to understand the hydrological processes and regimes influencing the regional hydrological cycle for proper water resource management and ecosystem restoration policies. In this study, we measured the patterns of isotopic values (delta 18O and delta 2H) of river/stream-water to assess the factors controlling its spatio-temporal variability and mean residence time in glacierized mountainous Upper Indus River Basin, India to better understand the significant hydrological processes and controls. The isotopic values of stream/river water exhibited significant spatio-temporal variance ascribed to changing physiographic, hydrometeorological, and climatic factors persisting at the local and regional scales. The slope and intercept of the River Water Line [delta 2H = (8.3 +/- 0.2) x delta 18O + (15 +/- 3.9, p > 0.001)] is higher than global meteoric water line and local meteoric water line of the UIRB, India. The seasonality in source water ratios suggested that stream water is more biased to winter precipitation. The estimated mean residence time in six sub-basins ranged from 188 +/- 17 to 387 +/- 38 days with the longest and shortest mean residence time observed in Indus (387 +/- 38 days) and Tangtse (188 +/- 17 days) sub-basins. The polynomial (second-order) relationship suggests that the variability in the paleo-precipitation delta 18O values reflect a change in the moisture source and/or upliftment along airmass transport pathways. Our study highlighted the significance of physio-graphical and hydrometeorological processes in controlling the spatio-temporal variance of stable isotopic composition of river/stream water bodies. The current research work also improved the knowledge and un-derstanding of the local and regional hydrological processes.