Precision snow cover and glacier mapping for runoff modelling in a high alpine basin

The runoff regime of high alpine basins will be affected in response to global warming not only by the seasonal snow cover but also by glaciers. Runoff peaks due to snowmelt will partially be shifted from the summer to the winter. The glacier melt will supply a higher amount of meltwater until glaciers finally disappear, if the temperature keeps rising. In order to evaluate quantitatively this effect, a method is presented to map separately the snow cover area, the gradually decreasing snow coverage on the glacier and the area of the exposed ice. The test basin Rhône-Sion (3371 km2, 491 4634 m a.s.l.) has been divided into 7 elevation zones in view of the large altitude range. The periodical satellite monitoring of snow and ice areas was carried out separately for each zone with high resolution optical remote sensing data which provide the capability to distinguish between snow and ice. The paper demonstrates the necessity of accurate glacier and snow cover mapping by adequate satellite sensors in order to predict snow and glacier conditions as well as the changing runoff regime in high alpine basins in the 21 century.