Cooling effect and control factors of common shrubs on the urban heat island effect in a southern city in China

Because the heat island effect can make cities warmer than their surroundings, it can make urban dwellers uncomfortable and even affect their health, which is particularly pronounced in developed cities in southern China. To reduce the heat island effect and improve the environment, various types of vegetation have been planted in the urban green belt. Though previous studies have been conducted on the beauty, air purification functions and cooling effect of vegetation, little is concentrated on the different cooling effects and control factors of various common shrubs on the heat island effect in cities. In this study, five of the most regionally common shrubs were selected to study the cooling effect in Guangzhou, southern China. The maximum surface temperatures of five shrubs and pavement were compared using infrared temperature sensors from April 1st 2019 to October 31st 2019. Results show that (1) All five shrubs showed noticeable seasonal variation, and the average surface temperatures of the five shrubs were between 38.0 and 42.2 °C during May–August and 30.7–34.1 °C during the other seasons (April, September and October);. (2) Murraya exotica L. exhibited the best cooling effect on the maximum surface temperature. Its value was 44.7 °C, and the absolute difference values of Murraya exotica L. (10.3 ± 1.7 °C) were higher than any other shrub during the study period; (3) Both the LAI (R2 = 0.57, p < 0.01) and plant height (R2 = 0.13, p < 0.01) are control factors of the cooling effect on vegetation surface temperature for the five shrubs. This study revealed the differences in the cooling effect and influencing factors of five regionally common shrubs on the heat island effect. Research on the functional characteristics of plants and plant selection in urban green belts has both theoretical and practical significance.