A comparison of three methods of mass-balance determination in the Tuyuksu glacier region, Tien Shan, Central Asia

A photogrammetric survey in 1998 formed the basis for compiling a map of the Tuyuksu glacier region in the northern Tien Shan, Central Asia. Comparison with a map from 1958 enables calculation of the change in glacier volume over 40 years. The results are compared with direct annual measurements carried out continuously since 1956. Central Tuyuksu glacier shows a mass balance of -12.6 m w.e. for the geodetic method and -16.8 m for glaciological measurements. In view of the high accuracy of the maps, the discrepancy can be explained mainly by deficiencies in the glaciological measurements. Application of the precipitation-runoff model HBV-ETH represents the hydrological method of mass-balance determination and delivers specific mass-balance losses almost twice those indicated by the geodetic observations. This discrepancy is suspected to be caused by erroneous runoff measurements. The volume balance derived by the geodetic method is used to calibrate both the glaciological and the hydrological method.