城市典型水域景观的热环境效应

Thermal environment effect of urban water landscape

城市热岛效应是当前快速城市化进程中最具代表性的生态环境问题之一。热岛效应进一步影响着城市气候变化与城市可持续发展。现存大量研究证明了土地覆被改变导致的热辐射变化及人为热释放共同作用产生了城市热岛。然而,当前对缓解城市热岛效应要素的研究并不多见。以上海市中心城区为例,首先基于SPOT5影像的分类,提取了城市水域景观,再利用Landsat 7的ETM+的热红外波段,定量反演了城市地表热环境温度,然后利用GIS的空间分析功能,探讨了城市水域景观对热环境的影响。研究揭示水域景观在城市热环境中表现出明显的低温效应,而面状水域景观的热环境效应要强于线状河流景观。面状水域景观对热环境影响随着与热岛中心距离的增加而明显降低,此外还受到周围土地覆被的影响。线状河流景观的宽度与流经区域共同决定了其对城市热环境的影响能力。因此,在城市规划设计中,从缓解城市热岛效应出发,水域生态功能区的形态与空间设置可作为考虑因素之一。

Rapid urban expansion has profoundly impacted on urban biodiversity, ecosystem functions, regional climate change, and the quality of life. One of the ecological consequences of urban expansion is the Urban Heat Island （UHI） phenomenon, which is formed when higher atmospheric and surface temperatures in urbanized areas are observed over the surrounding rural area. Urban thermal environment problems caused by UHI have some further impacts on energy consumption, human health and urban sustainable development. As a synthesis representation of urban environment effect, UHI is jointly determined by the physical properties of land surface and heat release by related socioeconomic activities. Within the urbanized area there are diverse landscape types, such as urban building landscape, road landscape, green space, water body, and so on. Among various urban landscape types, the thermal environment effect of water landscape is quite different. It is important to study how the water body might influence the urban thermal environment. The SPOT 5 and Landsat 7 ETM＋ images are applied to derive the spatial pattern of urban water landscape and land surface temperature in Shanghai, and spatial analysis technique will be used to explore the thermal environment effect of water landscape. An intense urban heat island effect is identified in Shanghai City, with its center located on the west bank of Huangpu River. At the same time, a cold island effect is detected for the water landscape patches and corridors. Statistical significance is not found between area and perimeter of water patches （or river corridors） and their impact on local thermal environment. However, the water patch has a stronger thermal environment effect than the river corridor. The impact of water patch decreases as the distance to UHI center increases. For instance, the temperature of water patch in Luxun Park （the closest to the UHI center among all water patches） is 3.65℃ lower than the average temperature of its surrounding region, with only 2.60℃ lower than the average temperature of the region where Century Park is located, which is much further to the UHI center. Besides the distance to the UHI center, the impact of water patch on nearby area is also determined by the land surface composition. For instance, the surrounding area with more vegetation has a lower temperature than the area with more impervious surface. River corridors also influence the local thermal environment. Huangpu River, Suzhou River, Yunzao River and Chuanyang River are compared based on a buffering method, with the river width and the location of the river corridor as the two key factors on the local thermal environment. Flowing through UHI center and with the largest river width, Huangpu River has much higher impact on the thermal environment of the surrounding areas. The findings in this study are helpful to provide some effective policy implications for urban planning and design.