Built environment dynamics, atmospheric circulations, and geographical context shaping urban microclimates: Mobile observational insights from Athens's complex basin, Greece

The fine-scale variability of urban microclimates plays a critical role in shaping heat stress vulnerability and informing targeted mitigation responses. The present study aims to advance understanding of how urban form and function, atmospheric circulations, and geographical features influence this variability by assessing intra-urban heat and moisture patterns in Athens, Greece—a Mediterranean coastal city with complex topography—using mobile observations, collected during a summer 2024 heat wave day, and a multiple linear regression modeling framework. This analytical approach incorporated five urban morphological and functional predictors, along with two landscape variables, while it used vapor pressure as the humidity-related dependent variable, offering a more physically consistent and thermo-physiologically relevant indicator of atmospheric moisture. Results revealed a dominant modulation by heat wave-amplified sea breeze dynamics during the early afternoon, contributing to spatial confounding effects and reducing the influence of urban structural and functional attributes. Notably, West Athens—a socially vulnerable and heat-exposed area—demonstrated enhanced daytime cooling potential due to more open building arrangements, although elevated water vapor content may counteract perceived heat stress relief. At early nighttime, cooling in vegetated urban areas became more evident, with the role of built environment dynamics becoming increasingly apparent and varying by location and Local Climate Zone context. These findings can support climate-just urban planning and guide future relevant research.