Difference in the secular trend and evolution in seasonal mean minimum and maximum temperatures within several groups of Swiss climatological stations

Using principal component and cluster analyses, over 100 Swiss climatological stations were assigned to several groups for 4 seasons, analysing standardised 20th century daily minimum and maximum temperatures. The resulting groups are justified, since the 20th century time series of the stations included in one group show identical variations, and the behavior of the groups can be explained in terms of altitude, topography and regional climate. For two groups in winter, the evolution of mean minimum temperature anomalies was analysed. These groups represent opposite characteristics in altitude (low or high), topography (flat or alpine) and population density (high or low). The analyses have illustrated that for the 20th century, the two groups can only be compared in their long-term trend, and the more stepwise than gradual warming since 1900. These steps in the warming intensity differ considerably for both groups. A further difference is the asymmetric evolution within the minimum temperatures in the low altitude group. This is due to a stronger increase in minimum compared to maximum values beginning in the middle of the 20th century. The high altitude group, however, shows a strong increase in the entire distribution within the past decade only. The fact that high altitude sites are more sensitive to changing temperatures makes them extremely vulnerable locations. The alpine biosphere, cryosphere and hydrosphere will certainly be affected by such changes, which in turn will impact upon mountain communities; these would have to cope with an increase in natural hazards and their economic consequences.