Christian Georges

The impact of glaciers on the runoff and the reconstruction of mass balance history from hydrological data in the tropical Cordillera Blanca, Perú

A 41 years series of runoff and precipitation data from the Peruvian Cordillera Blanca demonstrates the high hygric seasonality in this tropical high mountain range. In this area, glaciers have a crucial impact on runoff which is of essential importance for the highly populated and cultivated valley of the Callejon de Huaylas particularly during the dry season. Whereas the mid latitudes glacier runoff amplifies the seasonal variation of runoff, the effect of glaciers in the low latitudes is a smoothing one. It decreases clearly with the decreasing degree of glaciation. In addition, particular circumstances of this tropical environment allow the reconstruction of a glacier mass balance history from the hydrological data for the second half of the 20th century. It shows a high synchronicity with the global trend of periods with glacier mass loss and gain. Comparison with length variations of three individual glaciers indicate a rather fast reaction of these glaciers to changes in mass balance. Although the mass balance variations show some differences among the individual catchment basins, the over all trend is uniform. A general positive correlation of mass balance variations with SOI is obvious but not regular.

20th-Century Glacier Fluctuations in the Tropical Cordillera Blanca, Perú

Abstract The value of glacier fluctuations as indicators of climate change detection has been increasingly recognized in recent years. Tropical glaciers are of particular interest. The Cordillera Blanca in Perú (77°30′W, 9°S) is the largest glaciated area within the tropics. Its 20th-century fluctuations have been analyzed. The total ice coverage around 1990 was obtained using optical satellite data SPOT XS. Based on the 1990 results, inventories and estimates of the glaciation during the 20th century had to be corrected. The data in this paper illustrate the general ice retreat in the tropical Cordillera Blanca: 620 km2 in 1990, 660–680 km2 in 1970, and 800–850 km2 in 1930. The 1930 value documents the extent of glaciation shortly after an intense advance in the 1920s. The Little Ice Age extent is estimated as 850–900 km2. The ice recession during the 20th century was not constant but was concentrated in two periods. Strong ice retreat occurred in the 1930s and 1940s and intermediate retreat from the mid-1970s until the end of the century. The ice coverage at the end of the 20th century is considered to be slightly below 600 km2.

On the Mass Balance of Low Latitude Glaciers with Particular Consideration of the Peruvian Cordillera Blanca

Glacier mass balance studies in the low latitudes are rare and glaciological methods and terminology are basically adapted from mid- and high latitude conditions. The low latitudes are considered to be the tropics and, to some extent, the adjoining dry subtropics. The outer tropics are proposed as an intermediate zone with tropical character during the humid season and subtropical character during the dry season. Delimitations as well as respective climate and glacier regimes are discussed in order to distinguish them from each other and from the mid-latitudes. Different sensitivities of the glaciers can be expected and promise, in turn, a complex climatological interpretation of glacier fluctuations. For this, detailed mass balance studies on low latitude glaciers are required. The respective discussion is concentrated on the Peruvian Cordillera Blanca whose topographical setting provides both spatial and temporal subdivisions in humid and dry regimes in one region. However, theoretical considerations and field experience show problems for the determination of mass balance variables in the Cordillera Blanca and the low latitudes in general. The absence of annual temperature variations hinders the development of impermeable layers which can be identified as annual reference layers and which prevent meltwater from percolating into the firn body. Thus, a combination of ablation measurements and the application of the flux divergence method for the determination of accumulation is proposed.

Low Latitude Glaciers: Unique Global Climate Indicators and Essential Contributors to Regional Fresh Water Supply. A Conceptual Approach

Greenhouse gases in the atmosphere trap energy and, if their concentrations increase, e.g. from anthropogenic sources, the aggregate energy of the earth system increases as well. As a consequence, intensities of fluid dynamic processes (atmosphere and oceans), phase changing processes, biochemical processes, and the thermal status of the system will change in a complex and highly interactive manner. Manifold changes in local, regional and global climate are therefore to be expected, but are anything but easy to detect because: Firstly, climate itself is characterised by multi-scale dynamic variability of interacting processes and states. Thus, trends, fluctuations or changes can only be analysed for selected parameters and must be extracted from noise. Secondly, instrumental records, which concentrate on isolated parameters, are limited in time, and proxy-indicators, although covering longer time scales, show complex dependencies on climate, which can be difficult to interpret unequivocally. This paper emphasizes the role of low-latitude glaciers as i) climate proxies and ii) climate-dependent freshwater sources.