The impact of tree canopy cover and imperviousness on air temperature during summer using low cost sensors on public transportation in Rome, Italy

This study investigates the relationship between Air Temperature (AT), tree canopy cover, and imperviousness in Rome, Italy, using a novel approach based on low-cost sensors mounted on public buses. The system operates autonomously, requiring no on-site personnel, and provides continuous measurements across the entire urban area and at all hours of the day. Data were collected over 53 clear-sky summer days under stable meteorological conditions and aggregated onto a 500 m grid after quality control and normalization. Results show a statistically significant cooling associated with canopy cover only during the early morning hours, before the onset of the sea-breeze circulation, highlighting the role of mesoscale ventilation in suppressing local daytime cooling in coastal cities. At night, AT exhibits a strong linear increase with imperviousness, with differences up to 3.6 °C between fully urbanized and non-urbanized areas. The diurnal cycle of Urban Heat Island (UHI) intensity, derived from the imperviousness-based method, shows negligible values during daytime and peaks of 3–4 °C at night. Unlike previous assessments in Rome based on fixed monitoring stations, the dense spatial coverage provided by mobile measurements allows a more robust reconstruction of the diurnal UHI cycle and reveals that previously reported daytime UHI signals were likely influenced by sea-breeze-induced thermal gradients. By leveraging automated, citywide measurements with low-cost sensors, this study provides new insights into the spatial and temporal variability of urban heat and supports the development of targeted adaptation strategies. • Collected 1.8 million temperature data in 60 days using low-cost sensors on Rome buses. • Canopy cover up to 40% can cool morning air temperature by up to 0.5 °C on average. • At night, temperature rises linearly with imperviousness, by up to 3–4 °C on average. • Accurate estimate of UHI daily cycle intensity using these mobile measurements.