Heat waves, urban heat islands, and wellbeing and health: a mobile sensing approach – H3Sensing

While the number of heat wave days in France will likely continue to increase over the century, extreme heat is associated with excess mortality and morbidity in urban heat islands. The first objective of H3Sensing is to investigate outdoor environmental, building, dwelling, situational, and behavioral determinants of objectively assessed personal heat stress over daily movements during warm periods. We will explore environmental determinants associated with micro-urban heat islands at an unprecedented level of accuracy; we will assess building and dwelling characteristics associated with in-home heat stress; and we will examine how daily activities (trips, etc.) and practices (how people dress, manage heat at home) contribute to heat stress. The second aim is to investigate how these heat stress determinants and momentary and cumulated heat stress itself are related to physiological indicators, sleep, thermal discomfort, and well-being. Using a random sample of 33,501 dwellings drawn from the population Census, 200 inhabitants of Grand Paris will be followed over 4 day periods in April-May and June-September (this sample size provides adequate statistical power; we will be able to assess and correct deviations from representativity). Data will be collected over two years to increase the sample of high temperature days. Research assistants will use a detailed assessment sheet (defined from the a priori visit to 20 dwellings) to collect information on building and dwelling climatic characteristics. Participants will carry a GPS receiver, allowing us to conduct a detailed GPS-based mobility survey (also permitting to survey access to air conditioned), and to dynamically assess exposures in participants’ everyday mobility. To move beyond simplistic assessments of personal heat stress, we will assess it in an ambulatory way considering personal ambient temperature, humidity, wind speed, and radiant temperature combined into the innovative universal thermal climate index. Additionally, a meteorological station will be placed in the bedroom, while sensors measuring solar flux will be installed outdoor on the windows and balcony. Participants will also carry an accelerometer for the assessment of sleep patterns, and physiological sensors (cuffless blood pressure monitor, body temperature, galvanic skin response as a marker of sweating). Personal thermal discomfort, well-being, and sleep quality will be self-reported on the smartphone. An a posteriori phone questionnaire will collect detailed information on heat-related practices over the observation period. Participants will receive intensive support during the data collection. Analyses of short-term effects will use repeated measure models. Investigations of momentary objective heat stress as the outcome will use statistical techniques for complex mixtures to handle the wide set of exposures. Analyses of sleep quality, well-being, and physiological measures as the outcomes will use two complementary designs: fixed-effect analyses of matched observations in the warm and in the cooler periods for the same participants; and participant-level fixed-effect analyses of pooled observations in the warm period. Effects of environments, buildings, dwellings, practices, and activities on health outcomes will be decomposed into direct effects and indirect effects through personal heat stress, to isolate the heat stress pathway. We will ascertain gender differences in heat stress exposure and in the sensitivity of health outcomes to heat stress. H3Sensing brings together epidemiologists, urbanists, and climate scientists. As research-to-policy translation, experts in urbanism involved in the project will formulate concrete technical recommendations and practical solutions (in a pedagogical document of synthesis) to help urban actors willing to integrate considerations related to urban heat islands in their urbanistic regulations, public policies, and urban planning projects.