上海市绿地植被的吸热降温效益评估

城市绿地夏季高温时具有明显降温作用。但现有研究侧重降温效应观测及其影响因子解析,而对绿地降温效益与人居环境需求的空间一致性鲜有研究。以上海市为例,基于高分卫星影像与样地观测数据,采用植被蒸腾吸热经验模型评估了城市绿地夏季降温效益,并利用GIS空间分析技术量化了绿地降温效益与空气温度及人口分布的空间耦合程度。结果表明:2017年上海城市绿地面积为10.45万hm ²,夏季（6-9月）绿地植被吸热量可达8.49×10 ¹⁵ J,相当于节约夏季空调降温的经济价值为14.57亿元,其中46%和33%的绿地降温效益来自阔叶林与混交林;浦东新区、崇明区和奉贤区的绿地植被合计贡献了67%的降温效益,但虹口、黄浦、徐汇等中心城区绿地的单位面积降温效益较高。更需关注的是,绿地植被降温效益与人居环境需求表现出局部地区的空间不一致,其中28.62%的地区植被降温效益与空气温度处于低耦合状态,7.31%的地区植被降温效益与人口密度为低耦合水平,且均集中分布在中心城区。因此,重点提升中心城区绿地植被降温功能,并规划建设周边绿地降温效益的空间辐射通道,是上海城市生态空间优化的重要方向。

Assessment on the cooling effect of urban green spaces in Shanghai

The phenomenon of urban heat island has become a critical environmental issue in many large cities. The trees and vegetation in the urban environment help to cool urban temperatures, whereas previous studies have concentrated on the field observation and factor analysis of cooling effect from urban green spaces in hot summer, but few studies have quantified the spatial coupling relationship between human settlement demand and cooling effect provision. This paper evaluated the cooling effect of urban green spaces in Shanghai based on the high-resolution images and observed results of typical sites, and analyzed theirs space consistencies between cooling effect and air temperature or population distribution with the help of GIS techniques. The results showed that, the green areas of Shanghai reached 104.5 thousand hectares in 2017, and could absorb 8.49×10 ¹⁵ J of heat via evapotranspiration in summer, implying that the cooling effect saved 1457 million RMB for the electricity consumption of air conditioners. Approximately 46% and 33% of cooling effect were provided by the broad-leaved forest and mixed forest, respectively, and the green spaces in Pudong New Area, and Chongming and Fengxian districts jointly contributed about 67% of cooling effect, whereas the per hectare green spaces in districts of Hongkou, Huangpu and Xuhui presented higher values of cooling effect. Inconsistency, in particular, between cooling effect and air temperature or population density was observed in some parts of Shanghai. Around 28.62% of cooling effect from urban green space was loosely coupled with air temperature, and 7.31% of green spaces generated the low coupling between cooling effect and population density, especially the low coupling areas distributed mainly in the central urban regions. Therefore, we propose to enhance the temperature reduction capacities of urban forest in central district, and import the cooling effect from suburban green spaces through ecological corridors.