Royal Dutch Meteorological Institute; Ministery Of Infrastructure And The Environment

Publications, presentations and other activities
Uncertainty in the future change of extreme precipitation over the Rhine basin: the role of internal climate variability
by S.C. van Pelt (Wageningen UR), T.A. Buishand (KNMI), J.J. Beersma (KNMI), B.J.J.M. van den Hurk (KNMI),

Future changes in extreme multi-day precipitation sums will influence the probability of floods in the river Rhine basin. Climate projections of future precipitation changes are subject to large uncertainties. These uncertainties originate from three sources; model uncertainty, scenario uncertainty and uncertainty due to internal climate variability. In this study the influence of internal climate variability on the uncertainty of the changes projected by climate models at the end of this century (2081-2100) is quantified for a 17-member ensemble of a single GCM and for a set of 12 GCMs from the CMIP3 ensemble. All climate models are driven by the IPCC SRES A1B emission scenario. The single GCM ensemble contains only internal climate variability while the CMIP3 ensemble contains both internal and model variability. An analysis of variance (ANOVA) model is formulated to disentangle the contributions from models uncertainty between GCMs and internal variability. Both the changes in the mean and characteristics of extremes are considered. To estimate variances due to internal climate variability a bootstrap method was used for the CMIP3 ensemble, which resulted in an ensemble of time-series for each GCM. For estimation of quantiles of the distributions of extreme precipitation amount with long return periods the GCM simulations were post-processed to the local scale using an advanced non-linear delta change approach. This approach uses climate responses of the GCM to modify an observed (1961-1995) precipitation time series. The results show that internal climate variability is estimated to account for about 30% of the total variance in the projected changes in the mean precipitation and explains a larger fraction of the total variance in the projected climate trends of extreme precipitation. The discrimination between model uncertainty and internal climate variability for extreme precipitation is inaccurate due to the large uncertainty of the total variance. This study shows that for this study area an ensemble of 12 climate models is too small to distinguish the influence of model uncertainty in trends of extreme precipitation from that of internal climate variability and that considerably larger model ensembles are needed to successfully do so.

Bibliographic data
Pelt, S.C. van, T.A. Buishand, J.J. Beersma and B.J.J.M. van den Hurk, Uncertainty in the future change of extreme precipitation over the Rhine basin: the role of internal climate variability
Presentation: 11th International Precipitation Conference 2013, 30/6/2013-3/7/2013, Ede, Wageningen University (int.).
Abstract (html)