This repository contains the supplementary materials associated with the manuscript entitled "Unravelling Groundwater Contribution and Recharge Zones in the Ganga Headwaters: An Isotope-Based Assessment Using HydroMix" SM1_Stable Isotope Data.xlsx contains the stable isotopic compositions (δ¹⁸O and δ²H) of river, groundwater, and snow samples collected from the Upper Ganga Basin during four field campaigns conducted in 2019, 2022, 2023 and 2024. The dataset includes associated metadata, such as sampling location, geographic coordinates, elevation, and date of collection. SM2_HydroMix Input.xlsx contains the isotopic compositions of end-member sources and streamflow used as inputs to the Bayesian isotope unmixing model HydroMix v1.0. Model simulations were performed independently for each elevational segment and sampling month (February, April, June, and October) to capture seasonal and spatial variability in source contributions. SM3_HydroMix Output.xlsx contains the posterior distributions of source contribution estimates generated using the Markov Chain Monte Carlo (MCMC) framework implemented in HydroMix v1.0. The analysis was conducted by defining a likelihood function based on the tracer concentrations (isotopes) of the end-member sources and the corresponding mixture samples. The resulting posterior distributions represent the estimated source contributions and their associated uncertainties. SM4_Supplementary Figures.pdf contains additional figures, trajectory analyses, hydrometeorological datasets, and model outputs that complement the results presented in the main manuscript.