Abstract:Snow cover and glaciers are the most important long-term forms of water storage and, hence, the main sources of runoff during the ablation period for many alpine headwater basins. We therefore investigated the application of the conceptual, distributed hydrological precipitation runoff evapotranspiration hydrological response unit model (PREVAH) to the alpine glacierized headwater basin of the Upper Salzach (593 km 2 , 5% glacierized) river in Austria. Hourly meteorological data from 17 stations for a 6-year period were available for the calibration and validation of the hourly runoff simulations. Multi-criteria validation included hourly discharge, snow covered area (SCA), and glacier mass balances. SCA maps were generated from optical satellite images for six dates. These maps were compared to simulated maps of SCA to (1) calculate differences in SCA, (2) calculate altitudinal differences, and (3) show the ability to accurately model snow cover on different aspects. The differences between observed and simulated SCA for glacierized areas were between 1 and 9% during June and July, and between 10 and 36% during August and September observations. In general, the model overestimated SCA, which is the result of PREVAH not including redistribution of snow by wind or avalanches. The temporal variability of the simulated mass balance agreed well with observations from surrounding glaciers. Nash-Sutcliffe Efficiency Criteria (R 2 ) of the hourly discharge simulations were between 0Ð83 and 0Ð89 with the exception of the extreme summer of 2003 which had an R 2 of 0Ð74. Contributions of glacier melt (firn/ice melt) to annual total runoff were between 1 and 4%. Again, the exception was 2003, when glaciers contributed 15% of the annual runoff and 60% to the August runoff alone.

Abstract:The model for mountain surface processes, Alpine 3D, was applied to the Goldbergkees basin (2Ð7 km 2 , 52% glacierized) in the central Austrian Alps to model hourly discharge and glacier mass balance. Alpine 3D is a physically based model which focuses on snow-ice-soil energy and mass fluxes (without lateral, gravity driven flows) in rugged terrain. From the records of the Sonnblick observatory, located in the study area, a high-quality set of meteorological, glaciological and hydrological data could be provided to force and evaluate the model. A 1-year period was simulated starting from September 2004. The model results were evaluated using observations of the glacier mass balance and discharge at the catchment outlet. The spatial variation of modelled annual net mass balance of Goldbergkees shows good agreement to observed data. Significant deviations occur mainly at locations, which are presumably influenced by avalanche events or drifting snow. The quality of runoff simulation was estimated using the Nash-Sutcliffe model efficiency and the explained variance number. Both criteria demonstrate that the modelled catchment discharge is of satisfactory quality, despite the fact that the local mass balance is not well represented at all grid points.

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Abstract:This paper gives an overview on the regional hydrological impact of the heatwave, which affected Europe in the summer of 2003. We investigated the small, glacierized Goldbergkees basin in the Austrian Alps, which is situated directly beneath the high Alpine Sonnblick observatory (3106 m a.s.l.). We analysed the long-term air temperature time series and quantified the extreme anomaly of the mean summer (JJA) air temperature for 4Ð4 times the standard deviation of the long-term mean . The mean summer air temperature was 4Ð7°C. In 2003, the solid fraction of precipitation was only 35%. This was the lowest value observed from 1927 to 2005. To quantify the impact of the warm temperatures on the Goldbergkees glacier positive degree-day sums were calculated. The 'hot' conditions of the summer of 2003 rapidly melted the snow covering the glacier and finally melted the ice beneath. The winter balance of the Goldbergkees did not show anomalies. The specific net balance of Goldbergkees was 1Ð8 m water equivalent (w.e.) for the 2002/2003 period and has been the most negative observed. Snowmelt was accelerated by low albedo, which was a result of Sahara dust-falls. The hydrological response unit (HRU)-based model PREVAH was applied to simulate hourly runoff, which was observed at the outlet of this small and topographically heterogeneous basin. All components contributing to runoff were separated. The model was driven using hourly meteorological data gained from the Sonnblick observatory. Snow-and icemelt were modelled based on an advanced temperature index-based approach. The model was validated using observed glacier mass balance data. The maximum simulated icemelt rate was 2Ð7 mm/h (4Ð9 mm/h assigned to the glacier surface). During August 2003, glaciermelt contributed 81% to the total runoff.

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Abstract. When applying conceptual hydrological models using a temperature index approach for snowmelt to high alpine areas often accumulation of snow during several years can be observed. Some of the reasons why these "snow towers" do not exist in nature are vertical and lateral transport processes. While snow transport models have been developed using grid cell sizes of tens to hundreds of square metres and have been applied in several catchments, no model exists using coarser cell sizes of 1 km 2 , which is a common resolution for meso-and large-scale hydrologic modelling (hundreds to thousands of square kilometres). In this paper we present an approach that uses only gravity and snow density as a proxy for the age of the snow cover and land-use information to redistribute snow in alpine basins. The results are based on the hydrological modelling of the Austrian Inn Basin in Tyrol, Austria, more specifically the Ötztaler Ache catchment, but the findings hold for other tributaries of the river Inn. This transport model is implemented in the distributed rainfall-runoff model COSERO (Continuous Semidistributed Runoff). The results of both model concepts with and without consideration of lateral snow redistribution are compared against observed discharge and snow-covered areas derived from MODIS satellite images. By means of the snow redistribution concept, snow accumulation over several years can be prevented and the snow depletion curve compared with MODIS (Moderate Resolution Imaging Spectroradiometer) data could be improved, too. In a 7-year period the standard model would lead to snow accumulation of approximately 2900 mm SWE (snow water equivalent) in high elevated regions whereas the updated version of the model does not show accumulation and does also predict discharge with more accuracy leading to a Kling-Gupta efficiency of 0.93 instead of 0.9. A further improvement can be shown in the comparison of MODIS snow cover data and the calculated depletion curve, where the redistribution model increased the efficiency (R 2 ) from 0.70 to 0.78 (calibration) and from 0.66 to 0.74 (validation).

This paper presents a comparative study at a small and highly glacierized catchment area in the Austrian Alps, where runoff under the extreme hot and dry conditions of summer 2003 was simulated based on two different glacier extents: the 2003 glacier extent and the 29% larger 1979 extent. Runoff was simulated applying the hydrological water balance model PREVAH at a high temporal resolution. For this purpose, the catchment area was subdivided into hydrological response units based on digital elevation model and land-cover data. The model was driven by meteorological data from the observatory at Hoher Sonnblick, situated at the highest point of the catchment area (3106 m a.s.l.). We were interested in the effect the change in glacier extent would have on the annual and monthly water balance and the hydrograph of hourly discharges. Results of the 2003 and the hypothetical 1979 simulation show main differences in runoff for the period July-August depending on a higher ice-melt contribution. Due to the same meteorological input, both simulations calculate the same snow accumulation and snowmelt. Annual discharge in 1979 would have been 12% higher and hourly runoff up to 35% higher than in 2003.