Alpine precipitation in a tripled CO2-climate

A statistical model is constructed to determine the change in wintertime mo nthly mean Alpine precipitation due to a tripling of the CO2 concentration. The model is based on optimally correlated pairs of predictand (Alpine pre cipitation) and predictor (500 hPa geopotential) patterns which were determ ined from observational data by a canonical correlation analysis. The stati stical model is applied to the change in large scale climate simulated by a general circulation model (GCM for a 3 x CO2 concentration. The statistica l model predicts a change of Alpine precipitation of up to 6% of the observ ed monthly rainfall for a 3 x CO2 climate. A maximal increase of wintertime precipitation is obtained for the stations in the south of the Alps and on ly slight changes are predicted for the stations in the north of the Alps. it is found to be important to remove the area averaged change of the geopo tential simulated by the GCM and to apply the statistical model only to the spatial variation of the geopotential. The regional climate change estimat ed with the statistical model depends only slightly on the exact set-up of the model. Thus the error of the statistical model seems to be small in com parison with the uncertainty in the large scale climate predicted by the GC M for 3 x CO2 conditions.