Tracing 'Third Pole' ice meltwater contribution to the Himalayan rivers using oxygen and hydrogen isotopes

Global warming is adversely affecting the melting rates of Himalayan glaciers, which feed a number of large river systems in the Indian sub-continent. Regional scale assessment of glaciers and their link to rivers are mostly quantified using remote sensing data and modelling techniques. Here we present an alternative stable water isotope modelling approach. New oxygen and hydrogen isotopes (O-18/O-16 and H-2/H-1, expressed as delta O-18 and delta D) data from the headwater of Indus River were analysed with a comprehensively compiled delta O-18 and delta D dataset of Himalayan rivers to quantify the volumetric flow of glacier ice meltwater in the headwaters of the rivers Indus, Ganges, and Brahmaputra. The isotope mixing model reveals that the discharge weighted annual average glacier ice meltwater contribution in headwaters (>2000 m) of the Indus, the Ganges, and the Brahmaputra are 47 +/- 13 %, 44 +/- 13 %, and 29 +/- 10 %, respectively, which corresponds to a minimum of 33.5 +/- 6.5 Gt yr(-1) of melted ice mass. Our results show that annual glacier ice meltwater contributions vary across the river basins, with Indus River receiving the highest contribution. We conclude that stable water isotope modelling is an alternative approach to study regional scale glacier-river interactions to address the future impact of climate change over glaciated Himalayan catchments.