Drivers of summer extreme temperature trends in Europe: insight from three major heat waves using flow analogues

The increasing frequency of summer extreme temperatures in Europe has been attributed to atmospheric and thermodynamic changes, alongside their interaction. However, the role of dynamic changes remains uncertain, and the mechanisms driving future extreme temperature trends are not fully understood. This study investigates historical and future trends in atmospheric analogues associated with three major European heat waves: the 2010 Russian, 1972 Scandinavian, and 2003 French events. Then, using a multi-model large ensemble of climate projections, we decompose trends in extreme temperature occurrences into thermodynamic, dynamic and interaction components and assess the effects of global warming, internal climate variability, and inter-model differences. Results show that extreme temperature occurrences linked to the 2003 French heat wave analogues increased during the historical period, primarily due to the thermodynamic component and increasing analogue frequency. Models only partially reproduce these trends due to the underestimation of dynamic contribution. In the future, all models project a further increase of extreme temperature occurrences, primarily driven by the interaction term, which mainly reflects the combined effect of the strong co-evolving long-term trends in thermodynamic and dynamic conditions. For the 2010 Russian and 1972 Scandinavian heat waves, no definitive conclusions can be drawn due to large uncertainties from internal climate variability and inter-model differences. These findings provide further insight into the mechanisms driving extreme temperature trends in western Europe and emphasize the importance of considering all sources of uncertainty for a robust evaluation of climate model projections.