Abstract/Summary

Summer 2015 was marked by hot and dry conditions over Central Europe, and significant increases in temperature extremes. Model experiments indicate that high temperatures were caused by a combination of forced responses and internal atmospheric variability. Model simulations suggest that changes in SST/SIE and anthropogenic forcings explain about 2/3 (1.6oC) of the observed warming (2.4oC) and changes in hot temperature extremes over Central Europe relative to 1964-1993. Interestingly, when comparing 2015SST with 2015ALL simulations, the results indicate that the impact of anthropogenic forcings plays the dominant role. About 1/3 (0.8oC) of the observed summer mean warming and changes in hot extremes is not explained by the model mean response and consequently may have resulted from internal variability, principally through physical processes associated with precipitation deficits. Thus our results indicate that anthropogenic forcings set the conditions for the development of the 2015 heatwave in Central Europe, but that internal variability was an important factor in explaining its extreme character.