Effects of Street Trees on Building Facades: Vertical Temperature Patterns and Wall–Air Heat Exchange

As urban heat intensifies, street trees are used to moderate thermal conditions in built-up areas. Most previous studies have focused on pedestrian-level or horizontal cooling, leaving the vertical response of adjacent building facades less understood. We conducted 16 simulations of north–south and east–west street canyons. At a building height of 20 m, tree spacings of 13, 9, and 7 m were compared with tree-free references. Corresponding 9 m-spacing and tree-free cases extended the height comparison to 10 and 30 m. Facade temperature and wall–air heat exchange were evaluated from 08:00 to 18:00. For 20 m buildings with 9 m spacing, whole-facade cooling reached 0.89–1.05 °C and sensible heat release decreased by 7.97–16.16 W m−2. The 10–20 m wall bands above the canopy cooled by 0.77–1.22 °C. The south-facing 0–3 m wall in the east–west canyon nevertheless warmed by 0.67 °C. The heat-flux decomposition showed that a larger wall–air temperature difference increased heat release despite a smaller heat-transfer coefficient. Closer spacing strengthened whole-facade cooling, while lower-wall responses varied with building height and facade orientation. At fixed spacing, increasing building height enhanced cooling over the lower 10 m, most clearly in the east–west canyon.