AN ANALYSIS OF REGIONAL CLIMATE-CHANGE IN SWITZERLAND

An analysis of daily climatological data covering the period from 1901 to 1992 for four locations in Switzerland (Zurich, Lugano, Davos, and Santis) has been made. The study has highlighted the fact that climat e change this century is characterized by increases in minimum tempera tures of about 2K, a more modest increase in maximum temperatures (in some instances a decrease of maxima in the latter part of the record), little trend in the precipitation data, and a general decrease of sun shine duration through to the mid 1980s. The interannual variability i s generally large, and filtering of the data to remove high-frequency noise shows that the regional climate undergoes a series of fluctuatio ns of between 8 and 20 years' duration. The temperature change over th is century is of greater magnitude than the global temperature changes published in the literature, reflecting an amplification of the globa l signal in the Alpine region; warming has been most intense in the 19 40s, followed by the 1980s; the cooling which intervened from the 1950 s to the late 1970s was not sufficient to offset the warming in the mi ddle of the century. Pressure statistics have been compiled as a means of providing a link between the regional-scale climatological variabl es and the synoptic, supra-regional scale. These statistics show that pressure also exhibits a number of decadal-scale fluctuations, with th e appearance of a new and anomalous behavior in the 1980s; in this dec ade, pressure reaches annual average values far higher than at other t imes this century. The pressure field is well correlated with the Nort h Atlantic Oscillation (NAO) Index for distinct periods of the record (1931-1950 and 1971-1990) and is almost decorrelated from the NAO Inde x for the other decades of the century; this is indicative of transiti on from one climatic regime to another, dominated by zonal flow when t he correlation with the NAO Index is high. In the 1980s, when zonal fl ow over the North Atlantic is strong, episodes of persistent, anomalou sly high pressures (blocking highs) are seen to occur over Switzerland , particularly during the winter season. The difference between the zo nal and non-zonal regimes is particularly marked between the decade of the 1950s and that of the 1980s. The impact of this change between th e 1950s and the 1980s on a number of climatological variables has been investigated statistically in order to provide an illustration of the manner in which changes in synoptic regimes (i.e., 'climate change') impacts upon climate characteristics on a regional scale. The analysis shows that temperature, precipitation, snow depth, and sunshine durat ion are indeed sensitive to large-scale influences; not only can yearl y mean changes be quantified, but also seasonal and monthly fluctuatio ns.