城市蓝绿空间降温绩效评估及提升策略——以北京市为例

Evaluation and improvement strategies for cooling performance in urban blue-green spaces

绿地和水体对缓解热岛效应和改善生态环境效果显著,但因城市空间稀缺导致建设机会成本高,提升蓝绿空间绩效研究亟需深化。本文构建基于成本−收益分析的降温绩效评估模型,定量测量不同规模和类型的蓝绿空间斑块降温效果,以北京市为研究区,利用2010—2020年3期土地利用与地表温度数据,评估大于1 hm^(2)蓝绿空间辐射范围的降温绩效。主要研究结论如下:①研究期内北京市蓝绿空间面积不断增加,呈现由小型面积(Ac)(1≤Ac<2 hm^(2))为主向中型(2≤Ac<10 hm^(2))和大型(Ac≥10 hm^(2))转变;水域持续增加,而林地、草地和混合类型减少;三环以内老城区面积基本持平,而四环减少、五环增多。②根据缓冲区降温模型,北京市蓝绿空间的降温区范围不断增加,从类型结构上看,大中型蓝绿空间形成的降温区增加,而小型蓝绿空间的降温区减少;林地面积虽然减少,但其降温区面积却在增加,而水体降温区面积增长不及自身面积增长。③不同类型蓝绿空间绩效水平呈现先上升后降低的特征,小型和中型混合类型、大型水体的降温绩效比其他同等规模的绩效更好。因此,优化蓝绿规模和类型结构、调整空间形态布局、改善生态空间质量对充分发挥蓝绿空间降温效应起到重要作用,为城市生态环境改善与可持续发展提供新思路。

Green spaces and water bodies play crucial ecological roles in mitigating the urban heat island effect.However,the limited availability of urban space increases the opportunity cost.This study develops a cooling performance evaluation model based on cost-benefit analysis to quantitatively assess the cooling effects of blue-green space patches of various sizes and types.Using land use and surface temperature data from three periods between 2010 and 2020 in Beijing,the study evaluates the cooling performance and radiation range of blue-green spaces larger than one hectare.The key findings are as follows.First,Over the past decade,the area of blue-green spaces in Beijing has steadily increased,shifting from small areas(1≤Ac<2 hm^(2))to medium(2≤Ac<10 hm^(2))and large areas(Ac≥10 hm^(2)).While water bodies have increased,the areas of forests,grasslands,and mixed types have decreased.The area within the Third Ring Road has remained largely unchanged,with decreases within the Fourth Ring Road and increases within the Fifth Ring Road.Second,the range of cooling zones for blue-green spaces in Beijing has expanded.Structurally,the cooling zone created by large and medium-sized blue-green spaces is expanding,whereas the cooling area of small blue-green spaces is diminishing.Despite a decrease in forest land area,its cooling zone range has increased,whereas the area of water bodies has grown less than their cooling zones.Third,the performance levels of various blue-green spaces initially increase and then decrease,with small and medium-sized mixed types and large water bodies demonstrating superior cooling performance compared to other scales.Therefore,optimizing the scale and structure of blue-green spaces and rationalizing their spatial layout are crucial for maximizing their cooling effects.This study offers new insights for enhancing the urban ecological environment and promoting sustainable development.