Research on the Cooling and Humidifying Effects of Cinnamomum camphora Roadside Plantings in Wuhan and Optimization of Thermal Comfort

Street trees in high-density urban areas play a crucial role in mitigating the urban heat island effect and enhancing spatial thermal comfort. However, the cooling and humidifying effects of street trees are influenced by complex factors such as surface material, spatial enclosure, and street orientation, and the underlying mechanisms require precise quantification. This study focused on the typical Wuhan street tree species, the camphor tree (Cinnamomum camphora), conducting systematic field observations during hot, calm summer periods. Using a vertically stratified observation approach, we simultaneously collected microclimate parameters—including temperature, humidity, solar radiation—at three heights: the lower canopy layer, the human activity layer, and nearground level. This methodology aimed to reveal the vertical thermal regulation characteristics of street trees. Results indicate: Vegetated surfaces exhibit greater cooling and humidifying effects than hard surfaces; Enclosure conditions differentially affect cooling efficacy, with generally weaker effects in more open environments; East-west aligned trees demonstrated superior cooling compared to north-south alignments; The monitoring site with soft ground cover and plant-enclosed surroundings achieved the highest discomfort index reduction rate (1.62%) among all sites, with corresponding optimal daily average humidity (68.5%) and temperature (36.8℃), confirming the synergistic contribution of shade and humidity enhancement to discomfort index improvement. In summary, the cooling and humidifying effects of street trees result from multiple factors influencing both radiation shielding and transpiration cooling mechanisms. In urban street tree planning, prioritizing permeable ground surfaces like lawns on east-west streets and appropriately increasing plant spatial coverage density can maximize cooling and humidifying benefits during high-temperature periods. This effectively enhances outdoor thermal comfort for citizens and provides a scientific basis and design references for optimizing green infrastructure in Wuhan and cities with similar climatic conditions.