GCM driven simulations of recent and future climate with the Rossby Centre coupled atmosphere - Baltic Sea regional climate model RCAO

Typ: Rapport
Serie: RMK 101
Författare: Räisänen, J., /Hansson, U. / Ullerstig, A. / Döscher, R. / Graham, L.P. / Jones, C. / Meier, M. / Samuelsson, P / Willén, U


A series of six general circulation model (GCM) driven regional climate simulations made at the Rossby Centre, SMHI, during the year 2002 are documented. For both the two driving GCMs HadAM3H and ECHAM4/OPYC3, a 30-year (1961-1990) control run and two 30-year (2071-2100) scenario runs have been made. The scenario runs are based on the IPCC SRES A2 and B2 forcing scenarios. These simulations were made at 49 km atmospheric resolution and they are part of the European PRUDENCE project. Many aspects of the simulated control climates compare favourably with observations, but some problems are also evident. For example, the simulated cloudiness and precipitation appear generally too abundant in northern Europe (although biases in precipitation measurements complicate the interpretation), whereas too clear and dry conditions prevail in southern Europe. There is a lot of similarity between the HadAM3Hdriven (RCAO-H) and ECHAM4/OPYC3-driven (RCAO-E) control simulations, although the problems associated with the hydrological cycle and cloudiness are somewhat larger in the latter. The simulated climate changes (2071-2100 minus 1961-1990) depend on both the forcing scenario (the changes are generally larger for A2 than B2) and the driving global model (the largest changes tend to occur in RCAO-E). In all the scenario simulations, the warming in northern Europe is largest in winter or autumn. In central and southern Europe, the warming peaks in summer and reaches in the RCAO-E A2 simulation locally 10°C. The four simulations agree on a general increase in precipitation in northern Europe especially in winter and on a general decrease in precipitation in southern and central Europe in summer, but the magnitude and the geographical patterns of the change differ a lot between RCAO-H and RCAO-E. This reflects very different changes in the atmospheric circulation during the winter half-year, which also have a large impact on the simulated changes in windiness. A very large increase in the lowest minimum temperatures occurs in a large part of Europe, most probably due to reduced snow cover. Extreme daily precipitation increases even in most of those areas where the mean annual precipitation decreases.