On the role of urban trees in reducing building energy consumption

Urban greening is a primary strategy for mitigating the Urban Heat Island (UHI) effect, yet quantifying its impact on building energy consumption remains challenging due to the complex reciprocal feedbacks between the urban microclimate and building systems. This study investigates the influence of urban trees on air-conditioning (AC) energy demand across seven climatically diverse cities (Riyadh, Phoenix, Dubai, New Delhi, Singapore, Lagos, and Tokyo) during the hot season. We employ a coupled urban ecohydrological and building energy model (Urban Tethys-Chloris - BEM) to simulate varying urban densities, tree cover scenarios, and plant physiological properties. Our analysis isolates the relative contributions of shading, temperature reduction, and humidity alterations on AC loads. Results indicate that well-watered trees yield the highest average summer AC reduction (-17%) in hot-dry climates, driven predominantly by shading. In humid climates, AC demand decreased by 6% to 9%; however, vegetation-induced humidity increased dehumidification loads, particularly under high ventilation rates. In these regions, optimal energy savings were achieved at 40% tree cover. These findings provide critical insights for tailoring urban greening strategies aimed at minimizing AC energy demand to specific regional climates.