AbstractIn recent years, two major topics have emerged in regional climate modeling. One topic is the extension of regional climate models of the atmosphere to regional Earth system models. Specifically, the coupling of regional atmosphere-ocean models is an important step toward reducing the dependency of regional climate simulations on global models. The second topic is the decrease of the horizontal grid spacing such that convection can be explicitly computed. These topics present new challenges for the observational data used to evaluate the models. To date, gridded observation data on the kilometer scale have been only available over a few specific regions. The size of regional climate model ensembles has considerably increased in recent years. Thus, how to manage large datasets and how to select representative subsets are challenges that must be addressed. Comparatively, little progress has been achieved in the fields of boundary conditions and physical parameterizations.