城区公园绿地外部降温模型及其热岛效应的缓解机理研究

The urban heat island (UHI) effect is becoming more and more serious, which prevents lots of pollutants being dissipated timely and then leads to numerous ecological and environmental problems, such as the haze weather etc. Vegetations in urban parks just have significant cooling effect on surrounding temperature, which could effectively alleviate the UHI effect. However, its pattern and mechanisms are not clearly understood at present. Focus on these problems, this study chooses the vegetations of 12 urban parks in Guangzhou as the case areas. We intend to adopt the new data-detecting technologies and combine the advantages of two mainstream research methods (remote sensing and traditional field measurement) to study vegetation’s cooling effect on surrounding temperature; and then analyze the mechanisms between vegetation’s canopy shading function, evapotranspiration function and its cooling effect. On basis of above analysis, we simulate the energy transfer process from the edge of vegetations to surrounding spaces using the Energy Transfer Model by considering the contributions of wind factor. Finally, a quantitative cooling effect model of vegetations in parks on surrounding temperature is established, which is formed by the canopy shading factor and evapotranspiration factor. In combination with 3D laser scanner technology, this study further extracts the two- and three-dimensional characteristic parameters of vegetations in the 12 parks, and discusses the underlying relations between these vegetation characteristics and their cooling effects; and reveals the mechanisms of vegetations on alleviating the UHI effect. The conclusions will provide useful guidelines on the planning and designing of vegetations in urban parks in order to effectively alleviate the UHI effect. In summary, it is a new attempt to study on the quantitative cooling effect model of vegetation in parks on surrounding temperature using the above new technologies.

城镇热岛效应日益加剧，使得大量的污染物滞留在城镇内部无法及时疏散，成为诸如灰霾天气等多种生态环境问题的首要原因之一。城区公园绿地对外部空间的降温效应十分显著，能有效缓解城市热岛，但其对外部空间的降温规律和机理尚不清楚。针对上述问题，本项目选取广州城区12个公园绿地作为研究对象，引入新型数据探测技术，综合遥感和实测手段两种主流方法的优势，研究公园绿地对外部空间的降温规律，分析冠层遮阴、蒸散作用与绿地降温的机理关系。在此基础上，考虑风力作用，基于能量传输模型模拟绿地系统与外部空间的能量传导，构建以冠层遮阴和蒸散因子为表征的量化降温模型。进一步结合地面3D激光扫描仪，获取公园绿地二三维特征参数，深入分析公园绿地特征参数与其外部降温效应的内在关系，认知其对热岛效应的缓解机理，以期为面向缓解热岛效应的公园绿地规划提供参考依据。引入新型数据探测技术，开展量化的公园绿地外部空间降温模型研究是一次新尝试。

城区公园绿地对外部空间的降温效应十分显著，能有效缓解城市热岛，但其对外部空间的降温规律和机理尚不清楚。针对上述问题，本项目选取广州城区12个公园绿地作为研究对象，综合遥感和实测手段两种主流方法的优势，研究公园绿地对外部空间的降温规律，分析冠层遮阴、蒸散作用与绿地降温的关系，在此基础上基于能量传输模型构建具有物理意义的绿地系统降温模型，并进一步结合地面3D激光扫描仪，获取公园绿地二三维特征参数，深入分析公园绿地特征参数与其外部降温效应的内在关系。研究发现：（1）在一定范围内，公园周边温度与公园边界点温度的温差随着其远离公园边界距离的增大而增加，且增长趋势逐渐减缓，近似于一条过原点的三次多项式；（2）四种植被类型ET和LAI 均与其降温作用有着明显的相关关系.但与其他三种植被类型不同，乔灌草复合结构类型呈现出 “U型”的EI与降温关系以及倒“U”型的LAI与降温关系，表明其降温作用不再是不同单一类型（例如乔木、草地）降温作用的简单叠加；（3）基于能量传输模型构建的草地/灌木的单层降温模型和基于能量传输模型的乔木/复合林地的双层降温模型模拟效果良好，前者的模拟精度R2为0.8176，平均误差为5.5%，均方根误差为1.3K，后者的R2为0.9392，平均误差为3.4%，均方根误差为2.1K。（4）公园对外部的最大降温温差与公园的乔木面积、灌木面积、水体面积、生物量呈显著的正相关关系，与LSI呈显著的负相关关系，而与草地面积和长宽比相关度不显著。利用3D激光扫描仪辅助开展植被三维生物量，将遥感技术与实地观测结合研究公园绿地斑块中观尺度的降温效应，在华南地区乃至我国尚属首例。从绿地降温的根本原因（冠层遮阴作用和蒸散作用）入手，综合考虑能量传输规律和风力作用，探索性构建具有物理意义的公园绿地降温模型，在国内外绿地降温研究中是一个新的尝试，研究成果具有重大的创新性和研究意义。