Spatializing daytime street-level thermal exposure frequency profiles in urban areas during extreme heat events using the operative temperature index

This study aims to better characterize daytime thermal exposure in urban areas. A methodological framework based on Operative Temperature (top) is proposed as a relevant thermal index, chosen for its physically based formulation and its suitability for integration into existing socio-spatial vulnerability assessment protocols developed in previous studies. The approach is applied to the municipalities of Grenoble and Échirolles (France), focusing on daytime hours (05:00–19:00 UTC) during five extreme heat days in summer 2022. It is based on mean radiant temperature and wind speed simulations at metric-scale, and air temperature and relative humidity simulations at neighborhood scale using the open-source Urban Multi-scale Environmental Predictor framework. Comparison of t op with the Universal Thermal Climate Index (UTCI) and Physiologically Equivalent Temperature (PET) shows very strong correlations (median r = 0.976 and 0.994), indicating that the index reliably captures spatial patterns of thermal exposure under hot, dry, radiation-dominated conditions during the study period. An interpretive framework is then developed to analyze the thermal exposure frequency distributions at the street scale, from a pedestrian perspective, within urban blocks, named Street-level Thermal Exposure Frequency Profiles (STEP). Four distinct profiles are identified, closely associated with land cover and urban morphology. Areas with high thermal exposure frequencies mainly correspond to impervious and open surfaces, whereas vegetated areas exhibit lower exposure frequencies, with more pronounced exposure intensities in the early morning. Overall, under the climatic conditions investigated, t op can be considered a computationally efficient index with strong potential for operational use in thermal exposure assessment studies.