Empirical‐statistical downscaling of reanalysis data to high‐resolution air temperature and specific humidity above a glacier surface (Cordillera Blanca, Peru)

Abstract

[1] Recently initiated observation networks in the Cordillera Blanca (Peru) provide temporally high-resolution, yet short-term, atmospheric data. The aim of this study is to extend the existing time series into the past. We present an empirical-statistical downscaling (ESD) model that links 6-hourly National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data to air temperature and specific humidity, measured at the tropical glacier Artesonraju (northern Cordillera Blanca). The ESD modeling procedure includes combined empirical orthogonal function and multiple regression analyses and a double cross-validation scheme for model evaluation. Apart from the selection of predictor fields, the modeling procedure is automated and does not include subjective choices. We assess the ESD model sensitivity to the predictor choice using both single-field and mixed-field predictors. Statistical transfer functions are derived individually for different months and times of day. The forecast skill largely depends on month and time of day, ranging from 0 to 0.8. The mixed-field predictors perform better than the single-field predictors. The ESD model shows added value, at all time scales, against simpler reference models (e.g., the direct use of reanalysis grid point values). The ESD model forecast 1960-2008 clearly reflects interannual variability related to the El Niño/Southern Oscillation but is sensitive to the chosen predictor type.Citation: Hofer, M., T. Mölg, B. Marzeion, and G. Kaser (2010), Empirical-statistical downscaling of reanalysis data to highresolution air temperature and specific humidity above a glacier surface (Cordillera Blanca, Peru),

Technological Solutions for Climate Change Adaptation in the Peruvian Highlands

“…The range contains approximately 722 glaciers covering more than 723 km² [9]. Similar to the global trends, considerable glacier retreat has been documented in the Cordillera Blanca over the 20th century [6]. Studies indicate that the Cordillera Blanca has lost over 25% of its coverage since 1970, during which, the average temperature has increased 0.35°C -0.39°C per decade [8].…”

“…Studies conducted on tropical glaciers reveal that they are particularly sensitive to climatic changes [6]. Climate in the tropical Andes has undergone measurable changes over the past 50 years, with an observed temperature increase of approximately 0.1 °C per decade with a general temperature increase of 0.68 °C from 1939 to 2008.…”

“…In the tropics and extra-tropics, moisture availability is governed by the oscillation of the Inter-Tropical Convergence Zone, which creates variations in the amount of moisture received [6]. The climate of the Cordillera Blanca region features low thermal seasonality with an average annual temperature range from 0°C to 9°C, while diurnal variations in temperature are typically greater.…”

“…Studies indicate that the Cordillera Blanca has lost over 25% of its coverage since 1970, during which, the average temperature has increased 0.35°C -0.39°C per decade [8]. Persistent and accelerated glacial shrinkage in the Cordillera Blanca is anticipated for the future, with severe consequences for the region's water supply and those who depend on it [6].…”

“…More than 99% of all the world's tropical glaciers are located in the South American Andes, and roughly 70% of these are found in Peru alone [6]. The Cordillera Blanca is Peru's most extensively glaciated mountain range, with a quarter of the world's tropical glaciers in glacial valleys with elevations ranging from 3000 to 6800m [4,[6][7].…”