NESTED REGIONAL SIMULATION OF CLIMATE-CHANGE OVER THE ALPS FOR THE SCENARIO OF A DOUBLED GREENHOUSE FORCING

Simulated temperature and precipitation changes over western Europe fo r a scenario of doubled atmospheric concentrations of CO2 are presente d. The simulations are performed using a Limited Area Model LAM (RegCM 2) nested into a General Circulation Model (ECHAM3). Both model compon ents are operated at very high spatial resolutions- approximately 120 km for the GCM and 20km for the LAM; the LAM domain encompasses a regi on of 1100 x 1100 km squared. Climatologies for five January and five July periods have been simulated. Average surface (2 m) temperatures a re found to increase by 1.4 K in winter (January) and 3.9K in summer ( July); this latter figure is, however, largely dependent on a positive bias in the summer temperature fields of the driving GCM. Average pre cipitation changes are generally small in absolute values, but exhibit considerable spatial variability. Large precipitation amounts are see n to be shifted towards higher elevations with a corresponding reducti on in the 'upwind' areas. The results are discussed taking into accoun t the 'predictive skill' of the modelling system, which is derived fro m comparing the simulated present day temperature and precipitation fi elds to the corresponding climatological information. A method is intr oduced to assess the reliability of climate scenario predictions-such as those discussed here-on the basis of this predictive skill.