Thermal environment effect of urban water landscape

Abstract

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°C lower than the average temperature of its surrounding region, with only 2.60°C 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.