Atmospheric blocking and climate extremes in Germany in present and future climate

Abstract. Atmospheric blocking is linked to extreme weather and climate events like heatwaves, heavy rainfall, and calm weather. The statistical relationship between blocking and extreme events in Germany is quantified in atmospheric reanalyses ERA5, ERA-20C, and 20CRv3, and in historical and future CMIP6 climate simulations. This targets the reliability assessment of climate projections regarding extreme events in the 21st century. The analysis of the atmospheric reanalyses in the period 1961–2010 indicates that days with blocking see heatwaves 10–11 times and heavy precipitation events or calms 1.5 to 3 times more often than days without blocking. These empirical relationships are also seen in historical CMIP6 simulations for the large-scale phenomena heatwaves and calms, but not for heavy precipitation events (with odds only 1–1.5 times higher given a day with blocking than without). In the simulated future climate, the relationship of blocking with the three extreme event types changes only moderately. Inconsistent blocking trends in the projections, particularly in summer, obstruct the robust projection of extreme events in Germany despite the stable relationship between blocking and heatwaves and calms in most of the CMIP6 simulations. Furthermore, the results confirm the need for better representation of precipitation extremes in climate models.