Precipitation delivery in the tropical high Andes of southern Peru: new findings and paleoclimatic implications

The Cordillera Vilcanota in the southern Peruvian Andes has been the site of significant research focused on paleoclimatic reconstructions from ice cores (Quelccaya), past glaciations, climate-glacier interactions, and ecological and human responses to climate change. In this article, we analyse precipitation patterns in the region from 2004 to 2010 using twice daily precipitation observations from six regional climate stations and hourly observations of precipitation intensity from nearby Cusco International Airport. We also analyse atmospheric fields of temperature, wind, and moisture at 700 and 200 hPa from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset and create 72-h antecedent upstream air trajectories for the heaviest precipitation events using the National Oceanic and Atmospheric Administration (NOAA) Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Results indicate that the majority of annual precipitation across the cordilleras and inter-montane valleys alike occurs from nocturnal, regionally coherent rainfall events, inferred to be stratiform in structure, that occur in association with deep moist convection over adjacent Amazon lowlands. Low-level moisture (as inferred from the antecedent upstream air trajectories) for precipitation events can be supplied from a number of different regions, including from the northwest and west. The trajectory analysis reveals a strong dominance (83%) of precipitation events occur under weak flow regimes from nearby Amazon basin source regions, with 50% associated with trajectories from the northwest. In addition, the El Nino-Southern Oscillation (ENSO) signal reported in previous work in the central Andes is not necessarily representative of the Cordillera Vilcanota, where La Nina years (including 2007-2008) typically experience slightly below normal precipitation and El Nino years (including 2009-2010) are considerably wetter. These results are of particular value in understanding atmospheric signals registered in Andean low latitude ice cores, and point the way towards obtaining greater climatological inference from parameters preserved in annual snow and ice stratigraphy. Copyright (c) 2013 Royal Meteorological Society