Changes in the thermal stress across Europe between 1940-2023

Long-term changes (1940-2023) in thermal stress and its drivers in Europe were investigated based on the Universal Thermal Climate Index (UTCI) extracted from the ERA5-HEAT reanalysis. Furthermore, a vulnerability index was introduced to assess the impact of thermal stress. The results reveal a rapid continental shift in thermal stress toward milder conditions. Although cold stress is declining fastest in northern regions (more than 4 hours·decade[Formula: see text]), heat stress is intensifying across southern Europe (more than 3 hours·decade[Formula: see text]). Such changes are driven by an increase in 2 m air temperature (between 0.2 up to 0.6[Formula: see text]C·decade[Formula: see text]) and mean radiant temperature, particularly over northern and central Europe, and by changes also in relative humidity and wind speed. One of the key findings of this study is the decline in wind speed in specific areas of central and eastern Europe, leading to an increase in UTCI. Monthly analyzes show that winters warm the fastest (e.g., January cold stress decreases by 1.93%·decade[Formula: see text]), while summer heat stress peaks in July (0.27%·decade[Formula: see text]). In particular, the late spring months (e.g., May) also exhibit a positive trend, contributing to an extended warm season in Europe. Although European UTCI trends generally show a migration of thermal stress categories toward no to moderate-stress, city-level findings highlight more pronounced effects in continental cities such as Milan, Italy, and less pronounced effects in coastal areas like Madrid, Spain compared to cities of similar latitude. Furthermore, Heat Vulnerability Index reveals that highest vulnerability in southern and eastern Europe. These findings support policymakers in developing science-based measures to mitigate thermal risks, addressing both climatic and socioeconomic vulnerabilities in an era of rapid urbanization and climate change.