Mountain water cellars: a chemical characterization and quantification of the hydrological processes and contributions from snow, glaciers and groundwater to the Upper Mendoza River basin (~ 32° S), Argentina

Abstract. Abstract. Between 2010 and 2015 the Central Andes of Chile and Argentina (32–37° S) suffered the effects of a mega drought without precedents in the instrumental period, where 71 % of weather stations showed more than 30 % of rainfall scarcity in Central Chile. The Cordillera Principal geological province, in the Upper Mendoza River basin, receives almost exclusively winter precipitation originated from the Pacific Ocean moisture. In addition to the snow that precipitates in this area of 3023 km², there are 951 ice bodies, covering an area of 404 km². The Mendoza River flow provides fresh water for more than 1.1 million inhabitants in this agriculture based arid region. Given the high inter–annual variability of snowfall, strongly affected by ENSO events, and the aridity of the region, it is crucial to quantify the contribution from different water sources to the Mendoza River flow. Glaciers play an important role regulating water availability, with mass accumulation in wet and cold years, and melting in hot, dry years. Understanding their dynamics as a function of environmental variables will help us predict water availability under a changing climate. Combining the instrumental record of streamflow from glaciers and rivers, meteorological data, remote sensing of snow covered area and chemical analysis of different water sources, this study attempts to understand climatic variables that control thawing, and the hydrological contribution of different glaciers to the streamflow during a dry period. Isotopic composition allowed us to differentiate snowmelt from glacier ice melt. In addition, it was possible to detect contributions of summer rainfall from Atlantic origin, in their unique storms that reach the Cordillera Principal, even when they had not been registered at weather stations. Finally, with end member mixing analysis, the relative contribution from different water sources were quantified over time, showing the temporally increasing contribution of glacial and periglacial environments as the melting season progresses.