Scenario-Based Assessment of Urban Heat-Stress Risk in Vilnius, Lithuania

Urban areas are increasingly exposed to heat stress under climate change due to rising temperatures, ageing populations, and increasing population density in cities. This study assesses current and future heat-stress risk in Vilnius, Lithuania, using the Humidex index and the CLIMADA risk modelling framework. Historical heat-stress conditions are analysed using observational meteorological data, while future conditions are evaluated using five CMIP6 climate models under SSP2-4.5 and SSP5-8.5 climate scenarios for the mid and late 21st century. The risk assessment combines high-resolution Humidex-based hazard data, gridded population exposure, and age-specific vulnerability functions. In addition to temporal Humidex trend analysis, CLIMADA is used to estimate spatially explicit Expected Annual Impact and population-normalised impact indicators. The frequency of heat-induced stress has increased significantly—the number of days when the Humidex index was ≥30 has risen by 5.6 days per decade. It is projected that by the end of the century, the proportion of such warm-season days (April–October) will increase from 13.1% to 25.8% under the SSP2-4.5 scenario and to 41.6% under the SSP5-8.5 scenario. Spatial impact maps identify areas with elevated total and population-normalised heat-stress burden, while age-specific results show higher impacts among residents aged ≥ 65 years. Cumulative heat-stress burden, expressed as Expected Annual Impact, could increase by approximately 1.8–11.4 times. The framework provides a spatially consistent and age-sensitive approach for assessing urban heat-stress risk and supporting local climate adaptation planning.