Runoff in glacierized alpine basins results from the seasonal snow cover and from the glacier melt. Due to high resolution satellite sensors, it is possible to map snow cover and glacier areas in the basin of Massa-Blatten, 196 km^2, 1447 - 4191 m a.s.l. Depletion curves of snow covered areas were derived in six elevation zones. In addition, the date was determined when the glacier ice became exposed. Melt depths were computed separately based on experimental measurements with regard to snow and ice. With the use of the snowmelt runoff model SRM-ETH, the following input components to runoff were determined: seasonal snow cover including new snow falling on the snow covered areas; new snow falling on the snow-free area; rain; and glacier-ice. In order to evaluate the effect of the refined snow and glacier mapping on detailed melt computations, the runoff was computed resulting from i) the conventional runoff simulation based on integral snow and glacier areas and from ii) an advanced simulation taking into account the individual contributions from snow cover and glacier melt. A significant improvement of the accuracy of the runoff simulation was achieved.