Study On Green Space For Relieving Thermal Environment In Residential Areas

Urbanization is the inevitable result of the world’s economic growth and social development. By the end of2012, the ratio of urbanization already reached to52.6%in China. Urbanization, an artificial process that turning the natural land cover into impervious surface area, is significantly affecting environment at different scales. One of the most famous problems is the urban heat island effect. It is amazed that the urban heat island intensity of the metropolis in the world is too high, such as13℃in Berlin,6.9℃in Shanghai. Therefore, it is of great theoretical and practical significance to study methods and techniques to improve the urban thermal environment by greening.So, taking Shanghai city in China as example, the research is carried out by using satellite photos, high-resolution aerial photos and field measurement. The objectives of the research are:(i) to work out the quantitative methods to study and evaluate the effects of green space of city on thermal environment in residential areas;(ii) to provide the scientific basis to select the greening plants and their spatial layout for improving the thermal environment in residential areas from the large, medium and small scales.The main research work and results of this thesis are showed as:(1) As for block scale, the underlying surface has significant effect on the air temperature by using satellite photos. The results are showed as:In the internal and external environment of block, the surface structure has a profound effect on the air temperature. There are significant correlations between the average temperature in block and the ratio of the building area to underlying surface area and the ratio of the green area to building area. When the ratio of green area to ground structures area is lower than15%, the temperature could be significantly declined when increasing the green area. When the ratio of building area to underlying surface area is in30%- 90%, whenever the ratio rises by10%, the temperature in RA will rise by0.6℃.(2) As for residential area (RA) scale, the landscape index has significant effect on the air temperature by using satellite photos, high-resolution aerial photos and field measurement. The heat environmental index (HEI) and its model are established. The results are showed as:The temperature of RA is tightly correlated with its landscape index. There is a highly significant negative correlation of temperature of RA with the coverage of green, the tree layer ratio, and a significant negative correlation of the average area of green patch. There is cooling0.15℃of temperature of RA as increasing10%of coverage of green or10%of tree layer ratio. There is no cooling effect when the average area of green patch is smaller than100m2.Furthermore, in order to make the rapid assessment and analysis of heat environment of RA can be become a reality, HEI has been verified by in36residential areas.(3)As for plant community scale, the plant community and its micro-environment have significant effect on the air temperature by using field measurement. The multi factor regression equation of the plant community cooling effect is established. The results are showed as:The ability of different species in residential greening to decrease temperature is mainly correlated with the plant color, daily average transpiration rate, total leaf area and environmental factors, etc. The daily heat-absorbing values of Cinnamomum camphora and France Holly are more than40000kJ. In summer,the difference effect between the community and. the compared to lawns reaches the peak that is2.8℃. The main internal factor that affected the cooling ability of the plant community is the coverage of tree layer and shrub layer, the main external factor that affected the cooling ability of the plant community is the temperature and humidity of the environment.:when the environmental temperature is increased by1℃(maintaining33～43℃), the environmental temperature due to the plant community will be cooled down by0.22℃; when the humidity is decreased by10%, the environmental temperature can be cooled down by0.55℃. The relationship between the ability of cooling temperature and the structure of the plant community can be described by the equation which has been verified by being used to more than130plant communities: the average temperature cooled by the plant community△T=2.14xcoverage of T1layer+1.78×coverage of T2layer+1.44xcoverage of S layer+0.34xenvironment temperature+0.06xenvironment humidity-15.08.(4) When the surrounding temperature is higher than34℃, it is suggested that if the temperature in residential area will be cooled down more than1.5℃:on the big scale, the ratio of the green area to underlying surface area in the internal and external environment of block should be more than5%, the ratio of the building area to the green area in block should be less than30, the ratio of the building area to the green area in the area of500m external environment and1500m external environment should be not more than30and15respectively; on multistory residential areas, the coverage of green should be more than40%, the percentage of tree should be beyond50%, and the average area of green patch should be more than200m2;on the small scale,preferring trees and shrubs with larger value of heat-absorbing especially for arbor community,will help relieving the urban heat island effect and improving landscape effect.