Glaciers and climate change: Interpretation of 50 years of direct mass balance of Hintereisferner

Direct mass balance data of Hintereisferner glacier annually measured for fifty years were reanalyzed and bias-corrected. The glacier area and the patterns of the spatial distribution of specific mass balance were homogenized using the measured data and the current methods of modern mass balance analysis on Hintereisferner. The homogenized mass balance shows a good agreement with the geodetic and the hydrological mass balance. The comparison with modelled mass balance and measured temperature data showed that the homogenized mass balance correlated best with TS sum (R-2 = 0.76) followed by the simple degree-day sum (R-2 = 0.60) and the mean summer temperature (R-2 = 0.55). From that and from the calculation of the effects of albedo changes follows that the frequency and duration of summer snowfalls play an important role in the summer ablation of the glacier. The analysis of sub areas shows that at high elevations mass balance is dominated by the influence of winter precipitation. At low elevations, the increasingly negative mass balance was a result of the increase of the mean summer temperatures and the decrease of surface elevation. Between 1953 and 2003, the surface of the glacier tongue lowered by 160 m. This corresponds to a temperature increase of about 1 degrees C at the surface 2003 compared to the surface 1953. In the same period, the potential incoming solar radiation during the summer is reduced by the surface lowering. Comparing the effect of these two factors, the impact of the topographic temperature change on mass balance is much higher than the impact of increased shading. At higher elevations, the effect of topographic changes is small compared to changes in the mean surface albedo. The separation of glacier tributaries has been decreasing the inflow of ice to the main tongue. The mass balance of the glacier parts connected to the main tongue decreases faster than the mass balance of the total area. Therefore, the retreat of Hintereisferner is governed by a more negative mass balance than measured for the total area. (C) 2009 Elsevier B.V. All rights reserved.