Effects of Two- and Three-Dimensional Morphological and Structural Greening Characteristics of Street Trees on the Street Thermal Environment

Wei Yang; Mingjie Zhang; Zichen Zhao; Wenting Wang; Hai Yan

doi:10.54691/pjpwde21

Authors

Wei Yang
Mingjie Zhang
Zichen Zhao
Wenting Wang
Hai Yan

DOI:

https://doi.org/10.54691/pjpwde21

Keywords:

Street Thermal Environment; Street Trees; Three-Dimensional Greening Structural and Morphological Indices; Air Temperature; Scale Effect.

Abstract

Under extreme heat conditions, street trees play a vital role in mitigating the urban street thermal environment. However, the relative contributions of their two- and three-dimensional greening structural characteristics remain insufficiently quantified. This study examined the differential effects of two- and three-dimensional greening indices on street thermal conditions. Mobile measurements were conducted on typical streets in Hangzhou during the summer of 2024 to collect daytime and nighttime meteorological data. Fisheye images and semantic segmentation were used to extract greening structural indicators, which were classified into two- and three-dimensional metrics based on previous studies. The results showed that, compared with treeless streets, streets with high canopy cover reduced daytime air temperature by 2.76°C (p < 0.01). Three-dimensional indicators showed significant daytime cooling effects, with GVI, TVF, and CV most strongly associated with air temperature (Ta), whereas the two-dimensional indicator TCR showed a slight nighttime warming effect. The effects of street-tree greening structure on air temperature were spatially scale-dependent, with an optimal range of about 70–110 m; the best-fit interval was 100–110 m during the day and around 100 m at night. These findings provide empirical support for street-greening optimization and climate-adaptive urban design.

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