A MULTI-YEAR ANALYSIS OF STABLE ISOTOPES TO TRACE GLACIER MELT WATER IN THE CORDILLERA BLANCA, PERU

The rapid retreat of glaciers in the tropics will have many potential devastating consequences including decreases in water resources and hydroelectric power generation. The Callejon de Huaylas, Peru, is a 5,000 km² watershed that trends NW-SE over 130 km between 8º-10º S latitude and drains the earth's most glacierized tropical mountain range, the Cordillera Blanca. Our previous analysis estimated that upwards of 10-20% of annual and 40% of dry season discharge is comprised of glacier melt that is not replaced in the annual hydrologic regime. We present the results of a synoptic sampling campaign during the dry seasons of 2004 through 2007 with an objective to understand the controls on isotopic variability and to test the viability of using stable isotopes of water to quantify the contribution of glacier melt water to regional discharge. A total of more than 100 water samples were collected from rivers, groundwater, and glacial melt throughout the watershed and the stable isotopes of water (δ¹⁸O and δ²H) were measured. The stable isotropic distribution is strongly controlled by geospatial parameters, and in particular the maximum elevation and glacier coverage within sub-catchments. Combining historical runoff data and glacier coverage with the stable isotope results (normalized for an elevation effect) we estimate an average increase of 1.6 (± 1.1) % in the specific discharge of glacierized catchments from 2004 to 2006. These results confirm that short term glacial melt is increasing discharge in the Cordillera Blanca. The research demonstrates the utility of stable isotopes of water as a useful tool to trace glacial melt contributions to a large remote watershed where traditional measurements such as meteoric water sampling and stream discharge is very limited or non-existent.