Thermal percepts are multifactorial: a cross analysis of thermal monitoring data and qualitative surveys on elderly women in a French metropolis during heatwaves

Populations are more exposed to heat as heatwaves become more frequent, more severe and longer. Urban areas are particularly vulnerable to heat, given urban density, microclimates and the concentration of aged population. Since thermal percepts determine behaviours and adaptive capacities, understanding percepts appears key for assessing heat vulnerability and adapting prevention strategies. However, thermal percepts involves more than just thermal sensation. They encompass the processing and cognitive integration of all sensory stimuli that allow individuals to evaluate their thermal environment. Hence, the present contribution discusses the relationship between climatic parameters and thermal percepts, and highlights the factors influencing them. This work focuses on elderly women, which are particularly vulnerable to heat.

A field survey was carried out during the summer of 2023. The interdisciplinary survey included a thermal monitoring of dwellings, daily follow-up through diaries, and several semi-structured interviews with six women over 70 years old. On this basis, Spearman correlation coefficients were calculated between daily thermal percepts marks and the dwellings temperature and humidity, as well as with weather data from a peri-urban weather station, aggregated daily (mean, maximum, and minimum values). Correlations were then analysed in light of the recorded detailed interviews.

Results highlight no single correlation between thermal percepts and climatic parameters. Rather, significant differences are observed between individuals and between overheating periods. In relation to semi-structured interviews, these differences can be particularly explained by the perceived vulnerability and experienced physical symptoms. Various other factors were also highlighted as impacting on thermal percepts: time of day, sensory experiences of the place, activities performed, mental representations, expectations and overall well-being. Therefore, the multisensory and multifactorial nature of thermal percepts should be considered when assessing individuals' vulnerability to heat and designing prevention strategies.