Estimating glacier and snowmelt contributions to stream flow in a Central Andes catchment in Chile using natural tracers

Abstract. This paper presents a methodology for hydrograph separation in high elevation watersheds, which aims at identifying individual flow sources such as snow- and ice melt, rainfall and soil water. Daily summer and bi-daily spring water samples from the outlet of the Juncal River were analyzed for all major ions as well as stable water isotopes, δ¹⁸O and δ²H. Additionally, various water sources such as rain, springs, snow- and glacial melt were sampled throughout the catchment. A principal component analysis (PCA) was performed in order to reduce the dimensionality of the problem. Potential sources were identified in a two-component U space that explains 77% of variability. Hydrograph separation (HS) was performed through three models: (i) Isotopic model, (ii) Mixing–PCA model, and (iii) Informative–Bayesian model, with very similar results in each case. At the Juncal River outlet, summer flows were composed by at least 50% of water originating in highly glaciarized headwaters in 2011–2012 (a dry period in the Central Andes). Autumn and winter flows were highly influenced by soil water and affect total annual discharge. Before the high flow season, snow melt accounted for approximately 25% of streamflow, However during summer, when streamflow was highest, snowmelt contribution was minimal, while glacier melt and soil water were the most important sources.