Scenario-based analysis of the projected mean changes in the monthly frequency of hot days based on the latest CMIP6 simulations along European zonal segments

The potential changes in extreme hot temperature (represented by TX35, i.e. the number of days with maximum temperature above 35 °C) are analysed, using the latest global climate model simulations ensemble mean of CMIP6, available in the new tool of the IPCC, namely, the Interactive Atlas. The analysis is carried out over Europe with a special focus on Central and Southern Europe. Our aim is to evaluate the spatial patterns within the projected changes in the period 2081–2100 that can be further used in several sectors, e.g. in the health sector, which is especially affected by the potential increase of extremely hot conditions. For this purpose, the projected changes of TX35 are compared to the reference-period 1995–2014 for four available scenarios from the newest scenario-family, namely, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 representing different mitigation and adaptation challenges. As the projected increase is not limited to summer, the monthly-scale analysis is extended to the period from May to September. A novel approach is used to investigate the major factors in the projected changes, namely, six zonal segments are selected over Europe, covering the relevant parts of the continent with appropriate distances between them. The most important driving factors of the projected changes of TX35 are identified as follows: (i) the differences between regions due to their north-south or east-west locations (i.e. zonal and continental effects), (ii) elevation above sea level, (iii) the different anthropogenic effects (i.e. different scenarios). The results show that the key factor in the projected changes is the difference between anthropogenic effects. Furthermore, the sea-land surface differences also have substantial effect on the projected changes of TX35, especially in the southern regions. Continentality and elevation show only smaller effects overall.