High-Altitude Himalayan Meltwater Contributions Revealed by Isotopic Analysis

Melting glaciers provide crucial seasonal water to communities in high mountain regions. To project how mountain water resources will be impacted by glacial recession requires quantification of current contributions of glacier meltwater to streamflow. This is particularly challenging in monsoon-affected regions, where high glacier melt rates are synchronous with very high precipitation rates. Glacio-hydrological modelling provides a way of estimating meltwater contributions, but confidence in applied conceptual and numerical models is enhanced by observations. Here, stable isotope ratios of oxygen and hydrogen are employed in order to trace relative contributions of multiple sources to the flow of the Dudh Koshi river in northeastern Nepal. Integration of 45 new observations from river, glacial melt, and snow samples with 784 previous observations creates a comprehensive multi-season dataset; these data constrain a mixing model to resolve contributions to river flow that vary seasonally and along the river transect. Preliminary results from the new post-monsoon samples indicate the highest meltwater fractional contribution yet seen in this region.