Climatology and Long-Term Trends in Population Exposure to Urban Heat Stress Considering Variable Demographic and Thermo-Physiological Attributes

Previous studies assessing population exposure to heat stress have focused primarily on environmental heat loads without accounting for variations in human thermo-physiological responses to heat. A novel 30-year (1991-2020) human thermal bioclimate dataset, consisting of hourly mPET (modified physiologically equivalent temperature) values for diverse populations, was employed in the present study to assist in addressing this gap. Focusing on the Athens urban area (AUA), Greece, the climatology and long-term trends in acclimatization-based strong heat stress (accliSHS) experienced by average male and female adult and senior individuals during the warm period of the year (April-October) were investigated. Results showed that an average adult (senior) in AUA experienced, on average, approximately 13 (18) additional days with at least 1 h accliSHS in 2020 compared with 1991. The increasing rates per year were particularly pronounced for days with >= 6 h accliSHS, indicating a rise in the daily duration of heat stress in AUA from 1991 to 2020. Combining the variations in climate and demographics in AUA during the examined 30-year period, the long-term trends in >= 1 h accliSHS exposure for the study population types were further examined. This analysis revealed that seniors' exposure to >= 1 h accliSHS in AUA increased by up to +153,000 person-days x year-1 from 1991 to 2020. Increasing population aging was the main driver of this outcome, highlighting the urgent need for heat-health action planning in Greece.