Assessing the exposure of diverse populations to heat under a thermo-physiologically consistent approach in a large Mediterranean urban area

Population exposure to hot weather and heat waves endangers human liveability and survivability. The assessment of heat exposure spatiotemporal patterns in both recent past and future can provide essential guidance for targeted adaptation measures. However, existing studies on the topic focus only on environmental heat loads, using single meteorological variables (e.g. air temperature) or simple composite indices (e.g. heat index) to define heat. This diminishes the value of human physiological and behavioral responses to heat. Here, we extend the heat exposure concept to account for these factors and their variability among different population subsets when characterizing heat. For this purpose, we employ a novel, open-access 30-year (1991-2020) human thermal bioclimate dataset that includes hourly values of mPET (modified physiologically equivalent temperature) for diverse populations (https://doi.org/10.5281/zenodo.10893914). We focus on the Athens Urban Area (AUA), which consists of five regional units at the local administrative level, and it is situated in the eastern Mediterranean climate change hot spot. At a first stage, we analyze the long-term trends of acclimatization-based strong heat stress (accliSHS) experienced by male and female adults and seniors in the five AUA regional units. This stage of analysis accounts for accliSHS duration and frequency, as these factors are key in relation to adverse heat-related health outcomes. Then, we combine the mPET estimates with population data for each targeted group and regional unit to compute accliSHS exposure and assess its long-term trends. At this stage, contributions arising for variations in accliSHS and population sizes are decoupled and discussed, focusing on the differences between the examined populations and regional units in AUA. This work is conducted in the framework of the HEAT-ALARM research project and provides valuable insights with respect to population heat exposure for diverse groups of people under a comprehensive human-biometeorological context.