“…GCMs reported by IPCC) were not subject to such validation (the term "validation" does not appear in IPCC AR4) and, therefore, the reliability of the outputs of these models, that have been used to assess the impacts on water resources, is not tested. Recent independent studies on the validation of IPCC models (Douglass et al, 2008;Frank, 2008;Koutsoyiannis et al, 2008a) indicate a rather poor performance, especially on long-term (climatic) scales. Solely using different unvalidated models to produce ensembles of climate predictions (or projections, in IPCC's vocabulary), as is current practice in IPCC reports, does not provide a scientific basis for uncertainty estimation.…”