Future changes of bioclimate in Greece: Variations in thermal stress according to the Universal Thermal Climate Index (UTCI).

The climate change and rising global surface temperature present urgent, immediate challenges, particularly in Mediterranean regions, where bioclimate is shifting significantly. This study examines the future bioclimate in Greece by projecting changes in thermal stress from 2031 to 2060 relative to 1991-2020. Using the Universal Thermal Climate Index (UTCI) and bias-corrected data from the Coordinated Downscaling Experiment-European Domain (EURO-CORDEX), the thermal stress was assessed under Representative Concentration Pathways (RCPs) 4.5 and 8.5 greenhouse gas emission scenarios. Our findings indicate an overall increase in heat stress across Greece, especially during summer with UTCI equivalent temperatures increasing by 1.2 ± 0.1 °C under RCP4.5 and 1.6 ± 0.1 °C under the RCP8.5 scenario. Annual 'very strong heat stress' days increase by 2.9 % (RCP4.5) to 3.7 % (RCP8.5), with summer increases reaching 9.5 % to 11.7 %, respectively. 'Strong heat stress' days extend by 11.9-16.9 days yearly, while warm days and nights increase by 10-20 %. The most affected areas include inland mountainous regions and Greece's northern and western parts. The increase in heat stress highlights the growing need for effective adaptation strategies to mitigate the adverse impacts of rising temperatures on human health in the region.