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In the last couple of years, since 2005, a next version of the KNMI regional climate model RACMO has been developed and applied in a number of projects. This version, hereafter referred to as RACMO2. 1, constitutes an update of the RACMO2 cycle. The first version of this cycle, hereafter referred to as RACMO2. 0, was built on the ECMWF physics package from cycle 23r4 embedded in the semi-Lagrangian (sL) dynamics kernel of the Numerical Weather Prediction (NWP) model HIRLAM5. 0.6. This release of the ECMWF model also served as the basis for the ERA-40 project (White et al., 2004; http://www. ecmwf. int/research/ifsdocs/). The HIRLAM-5 project is comprehensively described in Undén et al.(2002). The performance of HIRLAM+ ECMWF physics when operated in forecast mode is assessed and compared with the performance of an operational version of HIRLAM by de Bruijn and van Meijgaard, 2004. The modifications implemented in RACMO2. 0 in order to improve its performance under present-day climate conditions have been extensively described by Lenderink et al., 2003. Version 2.0 has primarily been used in contribution to the EU-project PRUDENCE.

An important motivation to initiate the development of RACMO2. 1 was provided by the findings that RACMO2. 0 had a tendency to underestimate the occurrence of convective precipitation, in particular in Southern Europe and at the same time an overestimation of extreme values of daily precipitation amounts. The recent implementation in the ECMWF physics of a new trigger function for deep convection was expected to resolve this problem. Other considerations that led to the …