Spatio-temporal heterogeneity of noise reduction spectrum characteristics in street green spaces

Objective The noise reduction effect of street green spaces is influenced temporally by changes in visibility during leaf shedding and spatially by the plant configuration structure. This study aims to reveal the spectral characteristics and spatiotemporal heterogeneity patterns of the noise reduction effects in street green spaces with different plant configurations under continuously changing visibility conditions.

Method Taking street greenery vegetation as the research subject, measurement points were established alongside the road and behind the green space to collect sound pressure level data at different visibility stages and calculate the noise reduction effect. Through correlation analysis, influencing factors of the green space's noise reduction effect during the dynamic leaf-shedding process were extracted, and a linear model was constructed between the diameter at breast height, height of trees and shrubs, and the noise reduction effect.

Result (1) As traffic noise frequency increases, the noise reduction effect of street green spaces follows a “fluctuation (< 200 Hz) - stability (200-2 000 Hz) - increase (> 2 000 Hz)” trend. Visibility has a more significant impact on the reduction of high-frequency (> 2 000 Hz) traffic noise. (2) Under different plant configurations, the influence of visibility changes on noise reduction effects varies, generally showing a trend of decreasing noise reduction effectiveness as visibility increases. (3) The complexity of the vertical structure is relatively important for enhancing the noise reduction effect of street green spaces. When visibility is low to medium, green spaces exhibit better attenuation of high-frequency noise compared to mid-low frequencies, whereas when visibility is high, they show better attenuation of low-frequency noise. (4) When visibility is low, the noise reduction effect of green spaces is mainly influenced by factors such as hedge width, and the diameter at breast height and height of trees and shrubs. During the dynamic process of leaf shedding, the key factors affecting noise reduction are the diameter at breast height and height of trees and shrubs.

Conclusion Noise reduction by street green space plants showed significant spatial and temporal heterogeneity, and the influence of visibility on noise reduction effect varied significantly among different types of green spaces. This study enriches the theoretical foundation of noise reduction by street greening and provides a scientific basis for urban landscape design oriented toward noise control.