Assessing seasonal thermal environment of two tree species: Integrating modeling and in-situ data in hot-summer and cold-winter climates

Trees significantly contribute to improving the outdoor thermal environment during hot summers. However, their negative impacts during the winter months in hot-summer and cold-winter regions should also be considered. The current study investigates the seasonal effects of two common tree species on the thermal environment in such climates. In-situ measurements and numerical simulations were conducted on an open campus, and idealized experiments were designed based on the observations. Strategies involving tree selection to optimize the thermal environment year-round were proposed. Our findings show that evergreen broad-leaved trees, with their denser canopies, provide a more extensive and intense cooling effect throughout the year compared to deciduous broad-leaved trees. The benefit threshold for the canopy coverage of evergreen broadleaved trees is 40 %, and the efficiency threshold of deciduous broad-leaved trees is 10 %. At the same canopy coverage, deciduous broad-leaved trees create a larger area of suitable thermal comfort throughout the year and conserve more heating energy in winter (8.24 x 109 J/ha) compared to evergreen broad-leaved trees. We suggest that the use of deciduous broad-leaved trees is a more effective strategy for improving the thermal environment in hot-summer and cold-winter regions.