Heat stress in Greece in the future climate

Climate change is one of the foremost challenges confronting humanity, with far-reaching consequences for ecosystems, economies, and societies worldwide. The steady rise of global temperatures is a clear sign of our changing climate with wide-ranging consequences, affecting everything from weather patterns and biodiversity to resources and human health. This study, performed in the frame of CLIMPACT project (Grant Agreement: 2023ΝΑ11900001), examines the impact of temperature rise on human thermal stress over the following years using the Universal Thermal Climate Index (UTCI). UTCI combines meteorological variables into a single value estimated in degrees Celsius and assigns it to a 10-point scale expressing the degree of human thermal stress. The scale ranges from -5 (‘extreme cold stress’) to +4 (‘extreme heat stress’) and includes a neutral category (0 – ‘no thermal stress’) and levels of increasing cold and heat stress. Climate change projections of the UTCI were estimated at 12:00 UTC using bias-corrected data of air temperature, relative humidity, wind speed and global solar radiation derived from the EURO-CORDEX regional climate model (RCM) simulations for Greece region and at a spatial resolution of ~11 km (0.11°). An ensemble of seven regional climate model simulations (three different regional models driven by five different global models) was used for the reference period (1991−2020) and the future period (2031−2060) in order to examine possible changes of UTCI estimations in the future. Both RCP4.5 and RCP8.5 greenhouse gases emissions scenario hypotheses (Representative Concentration Pathways, RCPs) were examined. The results show an increase of projected mean UTCI ranging from 1 ◦C to 1.5 ◦C [mean ± standard deviation (sd) = 1.2 ± 0.1 ◦C] across the country by the end of 2060 according to RCP4.5. This change is intensified under RCP8.5, with a projected increase in mean UTCI ranging from 1.4 ◦C to 2 ◦C (mean ± sd = 1.6 ± 0.1 ◦C) across the country. Areas with higher increase of mean UTCI are mountainous regions of the inland Greece, the northern and western part of the country and the islands of the Ionian and eastern Aegean Sea. In the future period, Greece is anticipated to experience a reduction in the percentage of cold stress and ‘no thermal stress’ days and an increase in the percentage of ‘strong’ (by 0.9% - RCP4.5; 1.2% - ­ RCP8.5), ‘very strong’ (by 2.9% - RCP4.5; 3.7% - RCP8.5), and ‘extreme’ (by 0.4% - RCP4.5; 0.5% - RCP8.5) heat stress days. The increase of heat stress is particularly pronounced during summer when the increase in the percentage of ‘very strong’ heat stress days ranges from 9.5% (RCP4.5) to 11.6% (RCP8.5) and of ‘extreme’ heat stress from 1.3% (RCP4.5) to 1.8% (RCP8.5). The findings underscore the significant impact of climate change on human thermal stress in Greece, with notable increases in projected heat stress. These projections highlight the urgent need for adaptive strategies to mitigate the health risks associated with rising thermal stress due to climate change.