High end climate change impact on European runoff and low flows exploring the effects of forcing biases
Abstract. Climate models project a much more substantial warming than the 2 degC target under the more probable emission scenarios, making higher end scenarios increasingly plausible. Freshwater availability under such conditions is a key issue of concern. In this study, an ensemble of Euro CORDEX projections under RCP8.5 is used to assess the mean and low hydrological states under +4 degC of global warming for the European region. Five major European catchments were analysed in terms of future drought climatology and the impact of +2 degC versus +4 degC global warming was investigated. The effect of bias correction of the climate model outputs and the observations used for this adjustment was also quantified. Projections indicate an intensification of the water cycle at higher levels of warming. Even for areas where the average state may not considerably be affected, low flows are expected to reduce, leading to changes in the number of dry days and thus drought climatology. The identified increasing or decreasing runoff trends are substantially intensified when moving from the +2 to the +4deg of global warming. Bias correction resulted in an improved representation of the historical hydrology. It is also found that the selection of the observational data set for the application of the bias correction has an impact on the projected signal that could be of the same order of magnitude to the selection of the Global Climate Model (GCM)