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Climate models have provided driving data for impact studies for decades. However, the uncertainties related to the use of such data have typically not been sufficiently considered. We investigate how CORDEX climate simulations, which were corrected for bias based on MESAN reanalysis data for the period of 1989-2010, match the gridded observational data set E-OBS. Furthermore, we investigate whether the bias-corrected simulations contain significant residual bias (RB), which we defined as the bias exceeding the range of the observational uncertainty (U-obs) that emerges from differences between the two data sets MESAN and E-OBS. Because the reference period selected in climate change impact studies often differs from the period used for bias correction, we further investigated whether the RB and other performance metrics of the periods 1989-2010 and 1961-1990 differ. We conducted this assessment for whole Europe and for biogeographical zones.

Most of the used performance metrics show a good match of the simulations with MESAN in the period of 1989-2010. The comparison against E-OBS yields worse results, indicating a significant difference between the two observational data sets. Minor bias exceeding the range of U-obs (RB) occurred over large land areas of Europe in this period. Based on the analysis conducted for the period of 1961-1990, the RB is several times larger than that of the period of 1989-2010; the other metrics also show worse performances.

Our findings imply that both the selection of the reference climate data set and reference period warrant greater attention in impact studies. In particular, we recommend researchers to use a bias correction period as reference period in their studies. Alternatively, a new bias correction should be applied if any different period is to be used as a reference.