Consequences of climate change for runoff from Alpine regions

The water balance of Alpine regions is strongly determined by the storage of water in the form of snow and ice. On the basis of long time series of daily precipitation, air temperature and discharge, the conceptual runoff model HBV3-ETH9 was applied to various basins of the eastern Alps showing a glacierization of 0-80 %. Using the results of regional climate modelling under the assumption of doubling of CO2, the meteorological input data files were altered taking into account more frequent hot days and additional convective precipitation events during the summer months, and the consequences of these changes for daily discharge were evaluated. The results show that in regions with insignificant glacierization, runoff reacts primarily to changes in precipitation, and less so to rising summer air temperature. In highly glacierized basins, however, the same scenarios suggest strongly enhanced water yields in an initial phase. Higher flood peaks will result when high melt rates and heavy summer rains coincide. If glacier mass losses continue in the more distant future, the glacierized area will diminish and summer discharge will be gradually reduced, resulting in drastic water shortages in hot, dry summers once the glaciers have disappeared.