Climate variability in the Alps: first results on the analysis of snow precipitation trends from time series and satellite data.

Snow cover greatly influences the climate in the Alpine region and it is one of the most important parameters in the analysis of the climate change because of the interconnections with other phenomena: in fact a different distribution of snow precipitation during the winter season and a difference in the amount of snow at ground greatly influence energy, radiation and hydrologic budgets, as well as atmospheric circulation. The aim of this study is a climatological analysis of snow precipitation features in South-Western Alps in the last decades: for this purpose daily snow depth and fresh snow depth measurements performed in 111 ground-based meteorological stations of the Regional Agency for Environmental Protection of Piemonte, Italy (ARPA Piemonte) network are considered. Most of daily data still need to be validated and homogenized, then a selection of some significant time series will be analysed. A complementary information about the extension of snow covered areas is given by satellite data, that allow to reproduce large scale snow cover with spatial continuity and high spatial or temporal resolution, supplying the lack of data where there are no at-ground instruments. ARPA Piemonte developed a snow cover algorithm using Meteosat Second Generation satellite data: daily snow cover product has been first validated with at-ground daily measurements performed in Piedmont and Aosta Valley during the period January 2007-July 2008. Then, in order to extend the validation over the whole Alpine region, MODIS satellite data were used: in both cases the results are good. Now the challenge is to keep on improving snow cover algorithm in order to get a high level confidence snow cover product usable for climatological studies.