Mapping of Snow Cover and Glaciers with High Resolution Remote Sensing Data for Improved Runoff Modelling

The study presents investigations of the runoff from snow and ice, carried out in the high alpine basin of the Rhône river at Sion (3371 km2, 491 -4634 m a.s.l.). Using satellite remote sensing data, features like the snow coverage in the whole basin, the gradually decreasing snow coverage on glaciers and the area of exposed ice have been mapped. The periodical monitoring of the basin is based on Landsat-TM data enabling snow and ice areas to be distinguished. The satellite imagery has been geocoded with high accuracy and interpreted using supervised classification techniques. The satellite derived snow and ice coverages were supplied to the snowmelt runoff model SRM+G allowing to compare the different runoff input components: seasonal snow cover, new snow, rain and glacier-ice. Due to the high part of glaciers in the basin (17% glaciered) special attention has been paid to the melt conditions of ice in comparison with the melt conditions of snow. Conditions for a norm year in terms of normalized daily values derived for the time period 1961 to 1990 for snow cover depletion, temperature and precipitation have been established. Based on norm year conditions the effect of climate change was evaluated for the scenarios 2030 and 2100, which are characterized by increasing temperatures during winter and summer and increased precipitation during winter. The results show the influence of increased summer icemelt in the basin Rhône-Sion. INTRODUCTION Snowmelt runoff modelling in high mountain areas based on periodical snow cover mapping derived from earth observation satellites has been regularily reported in the last decades (Martinec 1973, Baumgartner et al., 1985, Kumar et al., 1991, Martinec et al, 1991, Seidel and Martinec, 1992, Rango and Martinec, 1999). Advanced methods of satellite data processing make it possible to account for specific features of glacier melt if high resolution iamges are available (Ehrler et al., 1997, Schaper et al., 1999, Schaper et al., 2000a, Schaper et al., 2000b). Apart from the improvement of runoff modelling, the independent computation of glacier melt is an important step towards evaluations of glacier behaviour with regard to global warming. BASIN RHÔNE-SION The selected test basin of the river Rhône at Sion has an area of 3371 km2 and ranges from 488 to 4634 m a.s.l.. The total area of glaciers (among them the large Aletsch Glacier) amounts to 580 km2 or 17%. The situation of the basin in the Swiss Alps is shown in Fig. 1. For the purpose of runoff modelling, the basin has been divided into 7 elevation zones with respective data listed in Table 1. As illustrated in Fig. 1, runoff from an area, including more than 35 glaciers, is collected by galleries and stored in the Grande Dixence reservoir with an storage volume of 400 x 106 m3. ICIWRM-2000, December 19-21, 2000, Roorkee, INDIA 1 Table 1: Elevation zones and glacier areas of basin Rhône-Sion. For the purpose of runoff modelling each zone is divided into glacier and glacier-free areas. Zone Altitude Range [m a.s.l.] Mean Altitude [m a.s.l.] Area [km2] Glacier Area [%] glacier glacier-free glacier glacier-free 1 488 1100 796 0 277.0 2 1100 160