CR prepress abstract  -  doi: 10.3354/cr00866

ABSTRACT: Fourteen regional climate models (RCM) have been driven by general circulation models (GCM) in FP6-ENSEMBLES to provide 17 fine scale (25 km) scenarios of the climate change 2021-2050. In a preliminary exercise, these RCMs have been driven by gridded observations (ERA40 reanalysis) to simulate as accurately as possible the 1961-2000 period. The quality of this reproduction has been used to calculate a weight for each model. Each individual model climate has an uncertainty due to the finite sampling (30 years). These spreads are combined by those weights to produce an ensemble uncertainty. We illustrate here the daily and climatological frequency distributions for winter and summer temperature and precipitation in three European cities. The distribution obtained by ENSEMBLES weights is compared with a distribution using equal weights, distributions using random weights, and distributions based on a single model. As far as the reproduction of the observed distribution (1961-1990) is concerned, there is no evidence that the ENSEMBLES weight system provides results closer to observation than equal weights or weights drawn at random. Considering a single model taken at random yields a quality score not better than the ensemble in the case of precipitation, and worse than the ensemble in the case of temperature. As far as climate change 2021-2050 is concerned, the use of ENSEMBLES weights instead of equal weights leads also to a similar response, at the daily time scale as well as at the 30-year mean time scale.