Abstract
Planting trees along urban streets is one of the most important strategies to improve the urban thermal environment. However, the net impacts of urban street trees on human thermal comfort and physiological parameters are still less clear. On three similar east–west orientated streets with different degrees of tree cover—low (13%), medium (35%), and high (75%), urban microclimatic parameters and human physiological indices for six male students were simultaneously measured on three cloudless days in summer 2018. The results show that the differences in tree cover were predominant in influencing urban thermal environment and comfort. The street with the highest tree cover had significantly lower physiological equivalent temperature (PET) and more comfortable than the other two streets. The frequency of strong heat stress (PET > 35 °C) was 64%, 11%, and 0%, respectively, for streets with low, medium, and high tree cover. For the six male university students, human physiological indices varied greatly across the three streets with different tree cover. Systolic blood pressure, diastolic blood pressure, and pulse rate increased with decreasing tree cover. The results also suggest that urban thermal environment and comfort had considerable impact on human physiological parameters. Our study provides reasons for urban planners to plant trees along streets to improve the thermal environment and promote urban sustainability.
Highlights
Urban heat islands (UHI) and global warming have presented a combined threat to urban residents’ health and well-being (Wu 2014; Kroeger et al 2018; Li et al 2018)
The results show that all urban microclimatic indices (Ta, relative humidity (RH), wind speed (Ws), and Tmrt) varied considerably from 9:00 to 19:00 among the three streets with different tree cover (Figs. 2, 3 and Table 3)
The results demonstrated that Ta, Tmrt and physiological equivalent temperature (PET) had a positive relationship with systolic blood pressure (SBP), diastolic blood pressure (DBP), and pulse rate (PR), indicating that they increased with an increase in urban thermal stress
Summary
Urban heat islands (UHI) and global warming have presented a combined threat to urban residents’ health and well-being (Wu 2014; Kroeger et al 2018; Li et al 2018). The urban thermal environment is predominantly related to the properties of streets to provide an engaging environment that assures comfort and enjoyment (Ginner et al 2015; Lee and Mayer 2018). Street geometry, such as street direction, building height-to-width ratios, sky view factor can essentially shape the urban thermal environment (Chatzidimitriou and Yannas 2017; Sharmin et al 2017; Qaid et al 2018). Planting trees along streets has been one of the main strategies to enhance the urban thermal environment (Revelli and Porporato 2018; Gebert et al 2019)
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