Large-scale heavy precipitation and its link to atmospheric circulation in climate model outputs over central Europe

Heavy large-scale precipitation events are associated with large negative impacts on human society, mainly as they may trigger floods and landslides. Therefore, it is important to better understand underlying physical mechanisms leading to extremes and how they are reproduced in climate models.

The present study evaluates ability of current climate models to reproduce relationships between large-scale heavy precipitation and atmospheric circulation over central Europe. We use an ensemble of 32 regional climate model (RCM) simulations with the 0.11° resolution, taken from the Euro-CORDEX project. The statistics are compared for the recent climate simulations (1951-2005) against observations from the E-OBS gridded data set to identify main drawbacks of the RCMs. The large-scale heavy precipitation events are defined as days with at least 50% of all grid points over the examined area with heavy precipitation (exceeding the 75th or 90th percentile of the distribution of seasonal rainy days). The association with atmospheric circulation types is investigated through circulation types derived from sea level pressure using airflow indices (direction, strength and vorticity). The analysis is carried out separately for summer (JJA) and winter (DJF) season.

The number of days with large-scale heavy precipitation per season in observations reflects the seasonal precipitation sums (the larger precipitation sum the more days). In winter, the large-scale heavy precipitation is mainly associated with the west, northwest, southwest and cyclonic circulation types while in summer with the cyclonic, north, southwest and undefined types (in the observed data). Some RCM simulations are not able to reproduce the number of days with the large-scale heavy precipitation events and their relationships with circulation, especially in summer.