热岛效应是快速城市化进程中最具代表性的生态环境问题之一，而城市绿地，作为城市热环境中的“冷岛”区域，被广泛认为是缓解城市热岛最直接有效的途径。如何使有限的城市绿地景观最大程度地发挥其包括降温效应在内的各项生态功能，获取更大城市热环境改善效益，是当前面临的紧迫课题之一。本研究以北京市六环内城市绿地景观为研究对象，综合运用遥感、地理信息系统、景观生态学、微气候流体力学模型多种技术手段，从城市整体绿地景观、典型绿地斑块（城市公园）及居住区楼间绿地三个规划尺度上对城市绿地结构与其热环境效应的关系进行定量研究，探索绿地缓解热岛效应的空间规律，旨在为绿地系统的布局优化、城市热环境的改善及生态城市的建设提供一定的理论及实践指导依据。论文的主要内容和取得的主要研究成果如下：（1）基于Landsat-5 TM遥感影像对城市地表热环境及植被覆盖时空演变规律进行研究，分析发现自1991年以来六环内地表热环境总体趋于恶化，而1999年后由于植被盖度的快速上升有所改善；城市高温区以二环旧城区为中心向外扩展，且扩展方向与北京城市扩张的时空方向基本一致；内外环热环境相对差异逐渐减小。（2）借助景观生态学中的景观指数，定量研究城市绿地空间布局特性对城市热环境的影响。结果显示，在所有结构因子中，绿地聚集度影响最大，绿地分布越聚集，热环境状况越好。其次为植被盖度，但当植被盖度超过30%后，城市热环境指数的下降趋势有所减缓。此外，绿地碎裂化程度越低，绿地斑块的连通性越强，绿地形状越复杂，则降温效果越好。（3）对城市公园这一典型绿地景观的热环境效应研究，分析其空间结构对公园内部及周边环境的降温效果。结果表明：公园作为城市热环境中的冷源，其内部空间结构决定了公园吸收外界的总热容，这就意味着公园对其内部及周边环境的降温效果呈“此消彼长”的规律。具体表现在：景观构成上，绿地及水体面积越大，越易形成较强的局地环流，对周边热环境造成的影响也就越大，但与此同时其对公园内部降温效应的影响就不明显；与此相反，绿量越高，公园对其内部降温效应越明显，但对周边热环境没有显著作用。斑块形态上，公园外围边界形状越复杂，公园内外热量交流越便利，公园对周边热环境影响力越强，但与此同时由于更多的外部干扰，一定程度上减缓了其内部降温效应。从空间布局来看，硬质地表及林地布局越分散，对公园内外的降温效果越好。因此，在公园建设中应根据不同的需求和目的合理设计其空间结构。（4）基于微气候流体力学模拟软件ENVI-met对不同景观绿化设计因子对微气候的影响进行模拟，结果表明：提高绿地率能够有效降低空气温度和改善人体舒适性，但当模拟区域内绿地率超过30%以后，绿地面积的再增加对高温时段局地热环境的进一步改善效果不再显著，该结论与城市尺度相一致；对于不同绿化组合类型，屋顶绿化从理论上可以有效地提高人体舒适性。草坪水体组合的热环境相对最差，乔木结构绿地对局地微气候的改善作用更为明显，但用水体替代草坪的绿化模式并未表现出明显的热环境差异；从绿化布局来看，对于乔木草坪组合，乔木较为分散的镶嵌布局热环境效应更好，其次是条形布局；而对于乔木水体搭配，乔木较为集中的基准布局能发挥更大的改善小气候效应。

Urban Heat Island (UHI) is one of the most representative ecological environmental problems during the rapid urbanization process. Urban greenspace, which is known as “Urban Cool-island”, has been considered as the most direct and effective measure in alleviating UHI effect. It is a very urgent task currently that how to make the urban greenspace landscape perform its ecological functions, especially the cooling effect, to the greatest extent, and achieve greater efficiency in the improvement of urban thermal environment.In this study, taking the urban greenspace landscape within the Sixth-Ring Road of Beijing as the research object, the impact of urban greenspace on the urban thermal environment was explored with the integrated use of various technical means including remote sensing, geographic information system, landscape ecology, and micro-climate fluid-mechanics model. In detail, the quantitative relationship between the spatial structure of urban greenspace and its thermal environment effect was analyzed from three spatial planning scales, including the overall urban greenspace landscape, typical patch (city parks) and small greenspace between buildings at the neighborhood scale. This study aims to provide some theoretical basis and practical guidance for the optimization of the greenspace system layout, the improvement of urban thermal environment and the construction of ecological city. The main research content and several conclusions drawn from the study are as follows:(1) The spatial-temperal evolution of the urban surface thermal environment and vegetation cover was analyzed based on Landsat-5 TM remote sensing images. Results showed that since 1991, the surface thermal environment within the Sixth-Ring Road tended to deteriorate in general, while it has improved slightly after 1999 due to the rapid rise of vegetation coverage. The area with the highest temperature expanded outward centered on the old town, and the expanding direction shifted from the urban center to east, north and south, and finally became uniform, which was consistent with the urban expansion trend in Beijing. The relative difference of the thermal environment between the central area and surrounding areas became smaller.(2) With the aid of the landscape index in landscape ecology, quantitative analysis was carried to explore the influence of urban greenspace layout characteristics on urban thermal environment. Results revealed that the degree of aggregation made the most contribution among all the structure factors, which means that the more gathered the greenspace distribution was, the better the thermal environment, followed by he vegetation coverage. But when the vegetation coverage exceeded 30%, the declining trend of urban thermal environment index began to slow down. In addition, the cooling effect of urban greenspace was better with the lower fragmentation degree, the stronger connectivity, and the more complex shape.(3) The effects of spatial characteristics of city parks on internal and external thermal environment were explored. Results showed that as the cold source in the urban thermal environment, the spatial structure of parks determined the total heat capacity absorbing from the outside, which means that the cooling effect on the internal and surrounding environment presented a counter-balance relationship. More specifically, from the perspective of the landscape composition, the park with more greenspace and water areas could form the stronger local atmospheric circulation, thus provided greater cooling effect on the external thermal environment, but meanwhile its influence on the internal park was not obvious. On the contrary, the higher the greenness, the greater the internal cooling effect, but no significant effect acting on the external thermal environment. With respect of the patch morphology, the park with more complex boundary shape had much easier access to exchange the heat inside and outside the park, which showed more distinct cooling impact on the surrounding thermal environment, but at the same time more external disturbance would mitigate its internal cooling effect. In terms of the spatial distribution, the more dispersed the impermeable surface arrangement and forest distribution were, the better the cooling effects on internal and external parks. In conclusion, the spatial landscape characteristics of parks should be rationally designed according to different construction purpose.(4) The micro-climate fluid-mechanics model, ENVI-met, was applied to simulate the impacts of various landscape planting design factors on micro climate. Modeling results showed that the increase of green ratio could effectively reduce the air temperature and improve human comfort, but when it exceeded 30%, the further improvement was not obvioud in the period with the highest temperature, which was consistent with the results drawn at the city scale. For different greening combination types, roof greening could effectively improve human comfort in theory. Lawn-water combination represented the worst thermal environment. The greenspace with trees showed the more significant improvement of local microclimate, but there was no apparent difference in local thermal environment with water replacing lawn. As to the greening layout, for the tree-lawn combination, mosaic layout with scattered trees performed better thermal environment effect, followed by the strip layout. In contrast, for the tree-water combination, the base layout with concentrated trees can play a greater improvement effect for the microclimate.