Street-level cooling effects of street trees in Toshima Ward, Tokyo: a field-based microclimate assessment

Street trees can contribute to urban heat adaptation, but their cooling performance depends on street form, surface conditions, and canopy structure. This study examined street-level cooling and humidifying effects at seven street-tree sites in Toshima Ward, Tokyo, using summer field measurements. Street-level data were compared with rooftop meteorological reference data, and Microclimate Influence Indices (MIIs) were developed from normalised air temperature and humidity differences. Cooling and humidifying effects were stronger on streets with more favourable geometry and trees with larger canopies and higher Plant Area Index (PAI). General linear models showed that air temperature and relative humidity differences were significantly associated with time period, ground surface temperature, and PAI. Overall, the findings show that street-level cooling depends on the interaction among canopy structure, surface conditions, and street morphology, and that MII is a useful framework for comparing microclimatic performance in heterogeneous urban settings.