高密度中心城区蓝绿空间冷岛效应及其影响因素——以北京五环路以内地区为例

蓝绿空间作为城市绿色基础设施的重要组成部分，对促进城市热环境健康、改善局地微气候具有重要作用。利用Landsat 8遥感影像、土地利用等数据，基于辐射传输方程算法、K均值聚类算法、相关性分析等方法，量化了典型的高密度中心城区--北京五环快速路以内地区的1199块1hm²以上的蓝绿空间冷岛效应的表征指标，并分析与蓝绿空间规模、形状复杂度、景观组成、环境组成、植被覆盖等要素的相关关系，还根据蓝绿空间的不同降温特性进行分类，探讨每类蓝绿空间在缓解高密度中心城区热岛效应中的独特作用、优势与机制。结果表明：（1）蓝绿空间的规模、形状复杂度、景观组成等景观要素与冷岛效应的关系显著，如总面积、绿地面积和水体面积与降温幅度、降温范围、降温服务呈显著正相关，与降温效率和降温速率呈显著负相关；周长与降温范围、降温服务呈显著正相关，与降温效率和速率呈显著负相关；周长面积比与降温幅度和降温服务呈显著负相关，与降温效率和蓝绿空间自身温度呈显著正相关，而形状指数则与降温范围和降温服务呈显著正相关。（2）蓝绿空间的环境要素与冷岛效应也存在相关关系。蓝绿空间之间会产生冷岛效应的协同与促进现象，蓝绿空间降温范围内的其他蓝绿空间的总面积与该蓝绿空间的降温幅度、降温范围、降温服务和辐射距离呈显著正相关，与蓝绿空间自身温度呈显著负相关。（3）蓝绿空间的总面积、水体面积、周长与降温幅度之间，周长面积比与降温效率之间存在阈值，为节约土地资源、保证降温效果，建议不应过多超过阈值。（4）基于蓝绿空间在降温幅度、效率、辐射距离等方面的差异，将蓝绿空间划分为4类。高密度中心城区蓝绿空间规划建设应充分评估区域降温需求，了解蓝绿空间降温现状，合理配置具有不同降温特性和优势的蓝绿空间，在土地和资金有限的情况下，充分发挥各类蓝绿空间的冷岛效应。本研究有助于政府和规划师摸清当前蓝绿空间冷岛效应的现状、问题和发展潜力，对理论和实践具有一定参考意义。

Blue-green space cooling effect and its influencing factors in metropolitan area: A case study on the area within the Fifth Ring Road in Beijing

The blue-green spaces, the essential component of green infrastructure, play an important role in promoting the health of urban thermal environment and creating a comfortable microclimate. The typical metropolitan area, the district within the Fifth Ring Expressway in Beijing, was selected as the study area. The basic materials in the study are the Landsat 8 remote sensing image, the land use data and building vector data. We utilized the radiative transfer equation algorithm, K-means clustering algorithm, correlation analysis and other methods to quantify the cooling effect indicators of 1199 blue-green spaces with an area of more than 1 hm². We analyzed the correlation between the landscape and environment metrics of the blue-green spaces, such as scale, shape complexity, landscape components, environmental components and vegetation coverage, and their cooling effect indicators. Then the blue-green spaces were classified according to the diverse cooling performance. Finally, we discussed the cooling functions, advantages and mechanisms of each category of the blue-green spaces. The results show that:(1) the scale, shape complexity and landscape components of blue-green space have a significant correlation with cooling effect. For example, total area, green space area and water area have the significantly positive correlation with the cooling intensity, cooling area and cooling service and have a significantly negative correlation with the cooling efficiency and cooling gradient. Perimeter of blue-green space has a significantly positive correlation with cooling area and cooling service and have a significantly negative correlation with cooling efficiency and cooling gradient. The ratio of perimeter to area has a significantly negative correlation with the cooling intensity and cooling service and have a significantly positive correlation with the cooling efficiency and the land-surface temperature of the blue-green space. And the shape index has a significantly positive correlation with the cooling area and cooling service. (2) There is also a correlation between the environmental components of the blue-green spaces and their cooling effect. The synergy and promotion of cooling effect occurs between the blue-green spaces. The total area of other blue-green spaces in the cooling area is significantly positively correlated with the cooling intensity, cooling area, cooling service and cooling distance of the blue-green space and is significantly negatively correlated with the land-surface temperature of itself. (3) There are thresholds among the total area, water area, perimeter of blue-green space and its cooling intensity and among the ratio of perimeter to area and cooling efficiency. In order to save the land resources, it is recommended that the indicators above don''t exceed the thresholds. (4) Based on the performance of cooling intensity, cooling efficiency, cooling distance and so on, the blue-green spaces are divided into 4 categories. We believe that before the blue-green space planning and construction in metropolitan areas, the government should evaluate cooling demand, understand the cooling conditions of blue-green spaces and reasonably allocate them with suitable cooling functions and advantages. Only in this way can all categories of blue-green spaces exerts the enough cooling effect with the limited land and funds. This study will help the government and planners to understand the current situation, find the problems and development potential of blue-green spaces cooling effect. And it also has some references for the relevant theories and practices.