Resolution dependence of circulation forced future central European summer drying

Climate model based projections suggest a drying of the central European summer climate toward the end of the century. In this study we investigate the influence of the spatial resolution of an atmosphere-only climate model (EC-Earth at two resolutions, similar to 25 and similar to 112 km horizontal) on the simulated summer drying in this area. High resolution models have a more realistic representation of circulation in the current climate and could provide more confidence on future projections of circulation forced drying. We find that the high resolution model is characterized by a stronger drying in spring and summer, mainly forced by circulation changes. The initial spring drying intensifies the summer drying by a positive soil moisture feedback. The results are confirmed by finding analogs of the difference between the high and medium-resolution model circulation in the natural variability in another ensemble of climate model simulations. In the current climate, these show the same precipitation difference pattern resulting from the summer circulation difference. In the future climate the spring circulation also plays a key role. We conclude that the reduction of circulation biases due to increased resolution gives higher confidence in the strong drying trend projected for central Europe by the high-resolution version of the model.