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As a major part of the urban green space system, street trees play a corresponding role in adjusting the thermal comfort of the environment and alleviating heat island effects. The correlation between the morphological structure and microclimate factors in the lower canopy of street trees was studied, using data that were captured with vehicle-borne LiDAR to model the morphological structure and geometric canopy features of six key street tree species in the built-up area of Zhumadian City, Henan Province. The regulating ability and differences of canopy geometry on cooling, humidification, shading, and Physiologically Equivalent Temperature (PET) were studied. Research shows that: (1) Canopy Volume (CV), Canopy Area (CA), Canopy Diameter (CD), and Tree Height (TH) have a linear negative correlation with air temperature, relative humidity, and luminosity. TH had significant effects on the air temperature and relative humidity (R2 = 0.90, 0.96), and CV and CD had significant effects on luminosity (R2 = 0.70, 0.63). (2) The oval-shaped plant (Platanus acerifolia (Aiton) Willdenow) had a strong cooling and shading ability, with an average daily cooling of 2.3 °C and shading of 318 cd/m2. The spire-shaped plant (Cedrus deodara (Roxb.) G. Don) had a strong ability to humidify, with an average daily humidification of 4.5%. (3) The oval-shaped and spire-shaped plants had a strong regulation ability on PET, and the daily average regulation values were 40.5 °C and 40.9 °C, respectively. (4) The CD of the oval-shaped plant had a significant effect on PET (R2 = 0.49), and the TH of the spire-shaped plant had a significant effect on PET (R2 = 0.80), as well as a significantly higher CV and Leaf Area Index (LAI) than other street tree species. Therefore, selecting oval and spire canopy-shaped plants with a thick canopy, dense leaves, and high CD and TH values as street trees can provide significant advantages in cooling, humidifying, and shading, and can effectively adjust human comfort in the lower canopy understory. This study is the first to apply LiDAR technology to the regulation of urban microclimate. The research results provide a theoretical basis and quantitative reference for street tree design from the perspective of outdoor thermal comfort evaluation and play a guiding role in the application of LiDAR to urban forestry research. [ABSTRACT FROM AUTHOR]

In the context of global warming, more and more cities are experiencing extreme Urban Heat Island (UHI) effects and extreme weather phenomena, but urban green spaces are proven to mitigate UHI. Most of UHI's research focuses on the large scale and uses remote sensing methods, which do not reflect the dynamic characteristics in detail and do not detect internal influencing factors of the green space cooling effect. Therefore, this study focused on Small Green Spaces (SGS), carrying out the measurement of the meteorological parameters (temperature, relative humidity, wind direction, wind speed, photosynthetic radiation) of the 16 sites in four types of coverage (Impervious surface; Shrub-grass; Tree-grass; Tree-shrub-grass) in a university campus. At the same time, the coverage characteristic parameters, such as Canopy Density (CD), Leaf Area Index (LAI), Photosynthetically Active Radiation (PAR), Mean Leaf Angle (MLA), of each plot were analyzed and compared. The results showed that there were significant differences in temperature among different coverage types in SGS. The biggest difference was concentrated in the noon period when solar radiation is strongest during the day. The difference between the four types of coverage with vegetation at night was small. The maximum air temperature difference among the four types could reach 8.9 ℃ and the maximum relative humidity difference was 28.5%. The cooling effect of the multi-layer vegetation-covered (Tree-shrub-grass) area was the largest compared to the impervious surface, indicating that tree cover was the core factor affecting the temperature. Temperature and relative humidity had a close correlation with surface coverage types and some plant community characteristics (such as CD and LAI). The cooling and humidifying effects of plants were also related to PAR and leaf angle. The results provide suggestions for green space management and landscape design. [ABSTRACT FROM AUTHOR]