ABSTRACT
The changes in snowfall patterns in the Alps during the last few years have widely raised public awareness to the possible consequences of global climate change. There are several scientific reasons why snow is, in fact, a significant factor in this context: first of all, snow plays an important role in the hydrologic cycle and can be affected significantly by climate change. It is likely that temperatures will increase over the next decades, influencing the snow cover patterns in alpine regions. Because of the different physical properties of the snow cover compared to non-snow-covered surfaces, the energy balance is changing with an increase in temperature and with a consecutive decrease of the snow cover, resulting in a feedback to the atmosphere. Additionally, changes in the snow situation can have serious economic consequences:
Melt-water in the Alps is stored in reservoirs and is used for electricity production (60 per cent of the electricity in Switzerland is produced by water power).
Tourism during winter time, in alpine regions an important economic factor, can be severely affected by such changes. Furthermore, the influence of changes of the snow cover duration on vegetation has to be studied carefully.
Recordings of alpine meteorological stations show a later start of snowfall and snow accumulation but no considerable change in snow depths. First comparisons of quick-look photos of NOAA-AVHRR (National Oceanic and Atmospheric Administration—Advanced Very High Resolution Radiometer) data have shown that after the mid-eighties, snow distribution in the Alps and the pre-alpine lowlands has changed drastically. This means that the same amount of precipitation is measured as before but the snow-rain level has been changed both spatially and temporally. The significant changes of snowfall patterns led to the idea of monitoring such changes on a long-term basis. The Alpine Snow Cover Analysis System (ASCAS) has been designed, therefore, to monitor the full range of the Alps. For detailed, quantitative calculations, five basins in Austria, France and Switzerland were selected representing different climatic regions (western vs. central vs. eastern, and northern vs. southern alpine climate).