Abstract:The Alps are often referred to as the 'water tower of Europe'. In Switzerland, many branches of the economy, especially the hydropower industry, are closely linked to and dependent on the availability of water. Assessing the impact of climate change on streamflow runoff is, thus, of great interest. Major efforts have already been made in this respect, but the analyses often focus on individual catchments and are difficult to intercompare. In this article, we analysed nine high-alpine catchments spread over the Swiss Alps, selected for their relevance to a wide range of morphological characteristics. Runoff projections were carried out until the end of the current century by applying the Glacier Evolution Runoff Model (GERM ) and climate scenarios generated in the framework of the ENSEMBLES project. We focused on assessing the uncertainty induced by the unknown climate evolution and provided general, statistically based statements, which should be useful as a 'rule of thumb' for analyses addressing questions related to water management. Catchments with a high degree of glacierization will undergo the largest changes. General statements about absolute variations in discharge are unreliable, but an overall pattern, with an initial phase of increased annual discharge, followed by a phase with decreasing discharge, is recognizable for all catchments with a significant degree of glacierization. In these catchments, a transition from glacial and glacio-nival regime types to nival will occur. The timing of maximal annual runoff is projected to occur before 2050 in all basins. The time of year with maximal daily discharges is expected to occur earlier at a rate of 4Ð4 š 1Ð7 days per decade. Compared to its present level, the contribution of snow-and icemelt to annual discharge is projected to drop by 15 to 25% until the year 2100.

In this study, we analyzed the 20 th century ice volume changes for 20 glaciers in the southeastern Swiss Alps. Our sample included different glacier geometries, sizes and exposures and allowed us to investigate glacier response to climate change. Using a distributed accumulation and temperature-index melt model, we derived mass balance time series in seasonal resolution from 1900. The model was calibrated using ice volume changes obtained from differentiating digital elevation models based on (i) terrestrial topographic surveys, (ii) the Shuttle Radar Topographic Mission (SRTM), and (iii) aerial photogrammetry. In-situ point measurements of annual mass balance and winter accumulation were available for some glaciers, and long-term discharge records were used for model validation. The rate of mass loss between 1900 to 2008 strongly differed between adjacent glaciers. Whereas large valley glaciers (e.g. Vadrec del Forno) showed average mass balances of up to-0.60 m w.e. a-1 , smaller and steeper glaciers (e.g. Vadret da Palü) exhibited slower mass loss in the order of-0.20 m w.e. a-1. Over the last century, the regional ice volume decreased by 47%, with strong differences between individual glaciers (30-75%). Using a combined model for 3D glacier evolution and stream-flow runoff driven by regional climate scenarios, we generated perspectives for the 21 st century. We determined a decrease in glacier area of 63% until 2050 and an increase in annual discharge over the next three decades for catchments with high glacierization. By 2100, the model results indicated a shift in the hydrological regime and a 23% decrease in annual runoff attributed to increased evapotranspiration and strongly reduced glacier melt contribution. Zusammenfassung: In dieser Studie analysieren wir die Eisvolumenveränderungen im 20. Jahrhundert für 20 Gletscher in den südöstlichen Schweizer Alpen. Unsere Auswahl enthält Gletscher verschiedener Typen, Größen und Expositionen. Dies ermöglicht eine Untersuchung der Reaktion der Gletscher auf die aktuelle Klimaerwärmung. Durch die Anwendung eines verteilten Akkumulations-und Temperatur-Index-Schmelzmodells werden Massenbilanz-Zeitreihen seit 1900 in saisonaler Auflösung berechnet. Die Kalibrierung des Modells erfolgt mittels Eisvolumenveränderungen. Diese wurden durch verschiedene digitale Höhenmodelle, basierend auf (i) topographischen Karten, (ii) der Shuttle Radar Topographic Mission (SRTM), und (iii) Luftbildauswertungen gewonnen. Für die Modell-Validierung kommen sowohl in-situ Punkt-Messungen der jährlichen Massenbilanz und der Winterakkumulation, die für einige Gletscher zur Verfügung stehen, als auch Langzeit-Abflussmessungen zum Einsatz. Die Rate des Massenverlustes zwischen 1900 bis 2008 unterscheidet sich stark zwischen benachbarten Gletschern. Während große Talgletscher (z.B. Vadrec del Forno) eine durchschnittliche Massenbilanz von bis zu-0.60 m w.e. a-1 aufweisen, zeigen kleinere und steilere Gletscher (z.B. Vadret da Palü) einen geringeren Massenverlust in der Größenordnung von-0.20...