紫金山森林公园降温效应影响因素

城市绿地是城市自然景观的重要组成部分,探讨不同影响因素对城市绿地降温效应的影响规律,有助于城市绿地的空间布局规划与管理,以便更好地缓解城市热环境。以南京紫金山森林公园为研究区,沿陵园路—中山陵方向选取了5个植被结构相似的林地作为观测点,并以水泥地面为参照点,利用HOBO小型气象观测站对温度、湿度和风速等因子进行定点同步观测,并分别采用LAI-2200植物冠层分析仪、鱼眼相机和GPS手持导航仪获取各观测点的叶面积指数、天空可见度和高程信息,然后采用统计分析和相关分析方法,分别对绿地降温效应的日变化规律及其影响因素进行了定量分析。结果表明:各站点的温度变化趋势基本一致;与参考点相比,5个观测点在白天均有明显降温效果,13:00—16:00降温效应最强,而晚上降温效果很弱,甚至出现轻微的保温效应;降温幅度随大气温度的升高而增大,随相对湿度和风速的增大而减小;绿地叶面积指数、天空可见度和高程等因子对绿地降温效应在不同时段会产生不同程度的影响:叶面积指数与天空可见度在9:00—19:00间对降温效应的影响作用较为明显,但由于高温的影响,午后(13:00—15:00)影响作用较弱;在夜间,高程是主要影响因子。研究结果可为城市公园绿地的合理布局与绿化建设提供依据和参考。

Analysis of factors contributing to the cooling effects of Purple Mountain Forest Park

Local climate changes are exacerbated in urban areas due to the rapid urbanization, which will accordingly worsen the urban thermal environment and cause series of eco-environment problems. Urban green spaces are multifunctional and can reduce temperature and mitigate the urban heat island effect. Previous studies have found that urban microclimate, vegetation types and the characteristics of green patches are all contributed to the green spaces cooling effects. Quantifying the relationships between these factors and green space cooling effects will help to guide the urban green space planning and design, and accordingly help to mitigate the urban thermal effect. In this paper, five woodlands were selected as the research spots, which have similar vegetation structure, and another spot which was mainly covered by cement was selected as the reference point. All of the six observation sites are in the Purple Mountain along the direction of Lingyuan Road to Dr. Sun Yat-sen's Mausoleum. The HOBO meteorological stations at fixed observational spots were used to get meteorological factors such as air temperature, relative humidity and wind speed. The LAI-2200 and fisheye photograph were used to capture the Leaf area index and sky view factor respectively, and the handheld GPS navigation was used to get the elevation of each study spots. The relationships between temperature reduction and related factors were analyzed using correlation analysis. The results indicated that: (1) The air temperature of each spot showed the same changing trend; (2) Compared with the concrete (reference point), all of the five woodlands had obvious cooling effect during daytime with maximum temperature reduction in the period of 13:00-16:00. However, it seems the cooling effect is weak at night, which may be because that woodlands have heat preservation effect during night; (3) The temperature reduction of all the research points showed the increasing trend with the rising of air temperature,and decreasing with inducing of relative humidity or wind speed; (4) The impact of leaf area index, sky view factor and elevation was different at different period of investigation time. Leaf area index and sky view factor had a comparatively obvious effect on the temperature reduction during 9:00-19:00, but the effect became weaker after noon (13:00-15:00) due to highest temperature of a day. However, during the night, elevation became the key impact factor and it showed a significant positive correlation with temperature reduction. Through the field investigation of the study area, the cooling effect characteristics were captured and the relationships between cooling effect and main related impact factors were quantified. The results can help us understand the factors contributing to the green space cooling effect and provide practical guidelines for planning urban green spaces to mitigate the urban heat island.