Different cooling effect of urban tree in global cities

Urban trees are increasingly recognized as a vital urban planning strategy for mitigating heat stress in cities facing climate risks worldwide. To improve the effectiveness of tree planning, it is essential to evaluate how their cooling effects vary depending on urban contexts. The effectiveness of urban trees in reducing temperature and climate risks (e.g., health risks, energy consumption) is influenced by various factors, including building morphology, location, and climate zone. However, a comprehensive comparison of urban tree effects across various global cities using urban climate models remains unstudied.

In this study, we simulated the cooling effect of urban trees in diverse cities with different climate zones and built environments, including Tokyo (Japan), Baltimore and Phoenix (US), and Telok Kurau (Thailand). Many urban climate models have simplified the cooling effects of trees, making it challenging to accurately estimate their impact. The CM-BEM (one-dimensional Climate Model and Building Energy Model) employs a mosaic of non-urban tiles to represent green spaces but does not account for interactions between urban trees and other urban elements. However, CM-BEM incorporates anthropogenic heat from buildings by simulating air conditioning use, providing a useful framework for comparing adaptation strategies between air conditioning and urban trees, which remains our future work.

To enhance the capability of CM-BEM in representing urban tree effects, we integrated a multi-layer tree canopy structure and simulated radiation and heat flux interactions between trees and urban structures. Our findings indicate that the cooling effects of urban trees vary across cities, with greater temperature reduction observed in densely built environments and drier climate regions.