Climate Change Studies for Germany and Europe Using High Resolution WRF Simulations

Abstract

During the 21$$\mathrm{{st}}$$ century, not only the global mean surface temperature but also the amount and strength of weather extremes will increase. This is mainly due to the continuous emission of greenhouse gases by human activities. Since warming over many land areas is larger than over the oceans, climate conditions will be regionally highly variable. In order to make regional projections of the climate in the future and to evaluate the ability of models to represent such phenomena, multi-model ensembles of regional climate simulations are required. This is e.g. realized in the World Climate Research Program initiated COordinated Regional climate Downscaling EXperiment CORDEX. The objective of WRFCLIM at HLRS is to contribute to these multi-model ensembles with simulations based on the Weather and Research Forecasting (WRF) model. Five simulations were carried out within the framework of the BMBF funded Project ReKliEs-De (Regionale Klimasimulationen Ensemble für Deutschland) for the simulation time period 1958–2100 at 12 km resolution. These simulations represent the first WRF climate projections which have been realized on the HLRS supercomputer yet. The results demonstrate that the ensemble members provided by the WRF provide an excellent contribution to the spread of the ReKliEs-De ensemble results. This gives a much better confidence not only in the estimation of the evolution of medians of atmospheric variables due to climate change but also in the estimation of extreme values such as hot and ice days. The corresponding climate indices provided by ReKliEs-De underline the importance for society and economy to mitigate climate change. Furthermore, within the CORDEX Flagship Pilot Study framework simulations are carried out between 1999 and 2014 at 15 km resolution further downscaling to the convection permitting (CP) grid on 3 km in central Europe to assess mainly diurnal cycles and high impact weather. The results and the performance analyses on the CP scale will be fundamental for to the set up and improvement of the next generation climate simulations. Therefore, HLRS and UHOH are prepared to contribute to a series of national and international projects concerning seasonal and climate simulations. The results highlight the necessity of CP simulations for next generation earth system models, and multi-model ensembles to assess climate change, as the latter provide indispensable uncertainty measures for climate change signals and extremes for Germany.