Along with air temperatures, the freezing level height (FLH) has risen over the last decades. The mass balance of tropical glaciers in Peru is highly sensitive to a rise in the FLH, mainly due to a decrease in accumulation and increase of energy for ablation caused by reduced albedo. Knowledge of future changes in the FLH is thus crucial to estimating changes in glacier extents. Since in situ data are scarce at altitudes where glaciers exist (above ~4800 m above sea level (asl)), reliable FLH estimates must be derived from multiple data types. Here we assessed the FLHs and their spatiotemporal variability, as well as the related snow/rain transition in the two largest glacier-covered regions in Peru by combining data from two climate reanalysis products, Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar Bright Band data, Micro Rain Radar data, and meteorological ground stati...

AP is supported by the “ Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica ” (Fondecyt - Peru), through the MAGNET research program. The collection of sampling was carried out within the framework of the “Impacto de la Variabilidad y Cambio Climático en el Ecosistema de Manglares de Tumbes” project. Supported by the International Development Research Centre of Canada under management of the Instituto Geofísico del Perú (IGP). WM is supported by research grants from the Brazilian Research Council (CNPq) . CJS is supported by the Australian Research Council ( DE160100443 , DP150103286 and LE140100083 ), in cooperation with Universidade Federal Fluminense . Project CTQ2011-28079-CO3-02 which is also supported with ERDF . We would like to thank Kelly Ronchi for the language revision.

Precipitation variability in tropical high mountains is a fundamental yet poorly understood factor influencing local climatic expression and a variety of environmental processes, including glacier behavior and water resources. Precipitation type, diurnality, frequency, and amount influence hydrological runoff, surface albedo, and soil moisture, whereas cloud cover associated with precipitation events reduces solar irradiance at the surface. Considerable uncertainty remains in the multiscale atmospheric processes influencing precipitation patterns and their associated regional variability in the tropical Andes—particularly related to precipitation phase, timing, and vertical structure. Using data from a variety of sources—including new citizen science precipitation stations; new high-elevation comprehensive precipitation monitoring stations at Chacaltaya, Bolivia, and the Quelccaya Ic...