Modelling and optimizing tree planning for urban climate in a subtropical high-density city

Urban trees affect urban climate via three processes: shading effect, evapotranspiration and wind resistance. However, large differences existed in the performance of different tree species and planting patterns. To quantify the effects of trees, we extended a heat-moisture coupled model by adding a new vegetation sub-model. The results showed that tree species with a higher leaf area index (LAI) and larger crown had a better capability of transferring sensible heat to latent heat. Sparsely planted trees provided a better cooling effect than densely planting pattern. The effect of trees was examined in urban areas with different densities. The effect of trees on urban wind environment depends on the building density of urban area. The large drag force posed by a high building density weakened the drag force of trees; thus, the negative effect of trees on urban ventilation was diminished in the high-density urban area. The negative effect of trees was also discussed from the perspective of urban moisture. This study demonstrates the need of strategic tree planting in terms of urban climate and provides insights into the creation of an urban greenery plan.