北京城市绿地群落结构对降温增湿功能的影响

The relationship between urban green space community structure and air temperature reduction and humidity increase in Beijing

清晰揭示城市绿地的空间布局与景观结构特征对其生态服务功能的影响对指导城市规划设计具有重要参考价值。目前国内外已有较多城市绿地降温增湿及其影响因素的实证研究,但是定量解析绿地群落结构与降温增湿功能关系的研究并不多见。本文基于北京市24个典型绿地群落夏季降温增湿效果的实测,重点解析了绿地郁闭度和绿量对降温增湿功能的影响,并提出了绿地结构优化配置的最优阈值。研究结果表明:北京城市绿地夏季日均降温幅度0.2~2.0℃,日均增湿幅度0.20%~8.26%;不同群落结构绿地降温效果上,乔灌草型>乔草或乔木型>灌草型>草地型;在绿地增湿效果上,乔木型>乔灌草>乔草型>灌草型>草地型;郁闭度和绿量对绿地降温增湿功能均有明显影响,但郁闭度影响更大,冠层郁闭度介于0.60~0.85、三维绿量密度≥5m^3/m^2的乔灌草或乔草型绿地具有最大降温增湿功能。

With rapid urbanization in China, large areas of vegetated surfaces have been replaced by impervious built surfaces. The development of urban heat islands （UHIs）has recently become a critical environmental issue in many cities. Fortunately, trees and vegetation in an urban environment can greatly improve microclimates and mitigate UHI development by reducing summer air temperature. Although many recent studies have observed such ecosystem services as temperature reduction and humidity increase by urban green spaces, the relationship between community structure of urban green space and air temperature reduction and humidity increase remains unknown. This study investigated 24 typical green space communities and observed their role in temperature reduction and humidity increases, and the relationship between these roles and canopy density and green biomass. The results showed that green areas in Beijing reduce summer air temperature by 0.2-2.0 ℃, and increase humidity 0.20%-8.26%. The urban green space with a Tree-Shrub-Grass structure can reduce temperature the most, followed by Tree-Grass and Tree. However, the urban green space with Tree structure increases humidity more than Tree-Shrub- Grass. There were clear relationships between canopy density and green biomass of urban green space and such roles as air temperature reduction and humidity increase. At the community scale, the canopy crown closure of green spaces had greater effects on urban temperature and humidity than green biomass. This study suggests that only when the canopy crown closure ranges from 0.60 to 0.85 and 3D green biomass density is larger 5m3/m2 can urban green spaces provide maximal microclimatic benefits.