The role of atmospheric circulation in explaining the summer extreme temperature trends over Europe

The frequency, duration and intensity of summer extreme temperatures over Europe are increased since the middle of the twentieth century. These trends are expected to further increase in the future due to global warming, which will influence both the thermodynamics and dynamics of these events. In this context, the role played by the thermodynamic changes on trends of extreme temperature events has been largely studied. Differently, the role of dynamic changes in explaining their historical trends as well as their future projections is still under debate.

In the present study, we assess the role played by dynamic changes on trends of summer extreme temperatures by assessing the trends in the occurrence of atmospheric circulation patterns (analogs) associated with the most severe heat waves during 1940—2022. Heat wave events are identified adopting the Heat Wave Magnitude Index daily (HWMId) as suggested by Russo et al. (2015). Furthermore, the trends in the number of summer extreme temperatures in the regions of the identified heat waves are decomposed as suggested by Horton et al. (2015), in order to evaluate the relative contribution of dynamic, thermodynamic and interactive terms on the total extreme temperature trends.

The analyses are performed using a multi-model initial-condition large ensemble, composed by CMIP5 and CMIP6 models forced with the Representative Concentration Pathway 8.5 (RCP8.5) and Shared Socioeconomic Pathways 585 (ssp585), respectively. This allows us to take into account both the global warming influence on extreme temperature trends and the uncertainties arising from model differences and internal climate variability. The analyses are performed for the time periods 1950—2010 and 2011—2100, in order to assess the role played by the different contributions on the historical and future trends of summer extreme temperatures, respectively.

Bibliography

Horton, D. E., Johnson, N. C., Singh, D., Swain, D. L., Rajaratnam, B., & Diffenbaugh, N. S. (2015). Contribution of changes in atmospheric circulation patterns to extreme temperature trends. Nature, 522(7557), 465-469.

Russo, S., Sillmann, J., & Fischer, E. M. (2015). Top ten European heatwaves since 1950 and their occurrence in the coming decades. Environmental Research Letters, 10(12), 124003.