Decoding the Individual Adaptive Response: Insights from Summertime Personal Heat Exposure, Thermal Perception, and Heat Response in Older Adults in Phoenix, Arizona

Adaptive responses to extreme heat involve conscious (behavioral) and unconscious (physiological) efforts to mitigate exposure, yet existing research often underrepresents vulnerable populations, such as older adults, and neglects adaptation measures. This study assessed intra- and inter-individual variations in personal heat exposure (PHE), thermal perception, and physiological responses among 39 individuals aged 45–74 from diverse socio-economic backgrounds and housing types (single-unit, multi-unit, and manufactured homes) in the Phoenix Metropolitan Area, Arizona.

Using HeatSuite™ system and Kestrel Drops, we monitored indoor (living room, bedroom) and outdoor PHE alongside health indicators (heart rate, blood pressure) and self-reported thermal perceptions during 21-day periods in the summer of 2024. Results reveal significant heterogeneity in indoor temperatures, driven by adaptive capacity and thermal preferences. Over 53% of the participants slept in temperatures exceeding optimal sleep conditions, potentially affecting their well-being. Manufactured homes were not always the hottest—single-unit homes with window units often exceeded comfortable thresholds. To translate PHE into a meaningful heat stress metric, we used a liveability metric to represent the highest activity intensity a person can do safely in their thermal environment. We estimate the impact of adaptive behaviors mitigating exposure by comparing liveability values from PHE in contrast to regional weather, with personal heat exposure supporting 1.84 ± 0.99 METs higher liveability compared to airport weather data. However, liveability gains varied significantly, with a 4.29 MET gap between the highest and lowest participants, suggesting socioeconomic disparities may outweigh housing type in shaping heat resilience. Ongoing multivariate analysis explores which adaptive capacities most strongly predict liveability differences, while thermal perception and physiological responses— such as thirst prevalence, blood pressure, and heart rate—are analyzed to assess whether similar factors influence thermal comfort and physiological stress. These findings enhance understanding of individualized heat resilience, providing insights into targeted adaptation strategies beyond environmental modifications.