Thermal Impact of Vehicles in urban canyons: Integrating Field Observations and Parametric Modelling in Lisbon.

The thermal impact of vehicle surfaces on urban climate is a critical yet understudied component, with the potential to influence local microclimates and the urban energy balance. This research quantified the thermal effects of vehicle surfaces in Lisbon, Portugal, through a combination of in situ measurements and parametric modeling. Using a compact mobile weather station equipped with precise sensors, we conducted both mobile and stationary measurements to capture detailed data on the radiative properties of vehicle surfaces. Results revealed significant variations in surface temperatures based on vehicle color. Black vehicles reached a median surface temperature of approximately 71°C, about 20°C higher than white vehicles, which had a median surface temperature of 45°C. This difference in heat absorption directly affected local air temperatures: black vehicles increased surrounding air temperatures by around 2.5°C on a summer day, while white vehicles caused a more moderate rise of 1°C. Black vehicles also exhibited the highest median net all-wave radiative balance (752.8 W/m²), while white vehicles showed much lower values (515 W/m²), illustrating darker vehicles’ greater thermal load and localized heating effects. When exposed to direct sunlight, dark grey vehicles showed the highest radiative balance values (median 680 W/m²), while white vehicles demonstrated the lowest values, confirming their reflective nature. To complement field measurements, we conducted thermal simulations using EnergyPlus integrated with Honeybee for Grasshopper. These simulations, calibrated with site-specific meteorological data, were used to assess whether the 3D EnergyPlus models could replicate real-world conditions. The results validated observed trends and deepened understanding of vehicle characteristics’ role in influencing surface and air temperatures. This study bridges the gap between empirical data and simulations, offering valuable insights for urban climate research and informing mitigation strategies to reduce urban heat island effects.