Relative contribution from different water sources to supraglacial runoff in western Himalaya.

• End member contribution on supraglacial runoff in the Himalaya. • Snowmelt contribution accounts for ∼ 70 % of supraglacial runoff. • Comparison of isotope-based results with a glacio-hydrological model (GHM). • Discrepancies in GHM and EMMA are attributed to subglacial complexities. Conservative tracers are often used in mixing models to estimate the contribution from different end-members to proglacial streams. The supraglacial runoff generated below the equilibrium line represents a combination of snow and ice melt, and rainfall, since additional mixing from englacial and subglacial drainage is not possible. Thus, supraglacial runoff offers a reliable proxy for the seasonal variations in end-member contribution to glacier-fed streams. In this study, we used stable water isotopes (δ18O, δD and d-excess) to estimate the seasonal variations in end-member contributions to the supraglacial runoff with a novel mixing model. During the early, mid, and late summer 2016, we collected and analysed the supraglacial runoff and its potential water sources: rain, ice, and snow. Accounting for fractionation processes occurring from solid to liquid phases, we calculated the isotopic signatures of the snowmelt and the ice melt. Based on our models, the supraglacial runoff was mainly composed of snowmelt (68.1 ± 7.9 %), followed by rainwater (16.6 ± 6.4 %) and ice melt (15.3 ± 6.1 %). Our results partially agree with those from a numerical glacio-hydrological based model estimates on the outflow of the same glacier. We discuss the slight discrepancies of the two modelling frameworks, and attribute them to the hydrological relevance of the subglacial aquifer system. [ABSTRACT FROM AUTHOR]