Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 22 4th EGU Alexander von Humboldt Conference "The Andes: Challenge for Geosciences" 2009 10.5194/adgeo-22-41-2009 http://www.adv-geosci.net/22/41/2009/ http://www.adv-geosci.net/22/41/2009/adgeo-22-41-2009.html http://www.adv-geosci.net/22/41/2009/adgeo-22-41-2009.pdf 41 49 2009-10-13 Characterizing contributions of glacier melt and groundwater during the dry season in a poorly gauged catchment of the Cordillera Blanca (Peru) M. Baraer michel.baraer@mail.mcgill.ca J. M. McKenzie B. G. Mark J. Bury S. Knox Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada Department of Geography, The Ohio State University, 1036 Derby Hall, 154 N Oval Mall, Columbus, Ohio 43210, USA Byrd Polar Research Center, the Ohio State University, 108 Scott Hall, 1090 Carmack Road, Ohio 43210, USA Department of Environmental Studies, University of California, Santa Cruz; 1156 High Street, Santa Cruz, California, 95064, USA The retreat of glaciers in the tropics will have a significant impact on water resources. In order to overcome limitations with discontinuous to nonexistent hydrologic measurements in remote mountain watersheds, a hydrochemical and isotopic mass balance model is used to identify and characterize dry season water origins at the glacier fed Querococha basin located in southern Cordillera Blanca, Peru. Dry season water samples, collected intermittently between 1998 and 2007, were analyzed for major ions and the stable isotopes of water (δ¹⁸O and δ²H). The hydrochemical and isotopic data are analysed using conservative characteristics of selected tracers and relative contributions are calculated based on pre-identified contributing sources at mixing points sampled across the basin. The results show that during the dry-season, groundwater is the largest contributor to basin outflow and that the flux of groundwater is temporally variable. The groundwater contribution significantly correlates (P-value=0.004 to 0.044) to the antecedent precipitation regime at 3 and 18–36 months. Assuming this indicates a maximum of 4 years of precipitation accumulation in groundwater reserves, the Querococha watershed outflows are potentially vulnerable to multi-year droughts and climate related changes in the precipitation regime. 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