| With the industrial development and the progress of urbanization process, the urban air pollution in China has become increasingly severe, and the pollution scale is gradually expanded. The urban air pollution has severely affected people’s health and life, and the air pollution problem is particularly prominent in calm-wind and high-density cities. By using the geographic information system (GIS), based on related theories and numerical methods of landscape ecology, environment science and urban ecology, with the roofs and their greening situation within the Second Ring Road of Chengdu as example, this paper studies the impact of roof ecological space under different landscape patterns on the air quality in accordance with the status quo of air pollution in calm-wind and high-density cities by combining the climatic adaptation analysis, landscape index calculation and landscape process simulation.Main research results and conclusion:first of all, we will review the status quo and development trend of calm-wind and high-density cities in China, and based on the urbanization and calm wind trend, the Chinese cities currently with a population over 500,000, accumulative annual wind speed smaller than 2m/s and the prevailing wind direction of calm wind as calm-wind and high-density cities. Secondly, by using the Google Map of the remote-sensing image of the area within the Second Ring Road of Chengdu and the GIS technology, the manual extraction and numeric method are used to obtain and analyze related data, and we find that:within the Second Ring Road of Chengdu, the total roof area is 1059.1hm2, accounting for 17.6% of total area; the roof greening area is 142.2hm2, with greening rate of 13.4%; the roof greening rate between the First and Second Ring Roads is significantly higher than that within the First Ring Road; the downtown area has the lowest data. Thirdly, based on the analysis of pollution status quo and the calculation of main degradation pathway contribution rate, by combining the planning of urban green space system and the distribution of heat island intensity, efforts are made to discuss the climate adaptation planning problem of roof greening system under the urban scale. We obtain the planning scheme and propose the planning key points:in order to eliminate the air pollution, the layout should benefit urban ventilation; the heat island circulation can be used to produce wind through reasonable layout; the roof greening can be used to disperse the area with high density of pollution. Fourthly, in accordance with the specific space structure and characteristics of urban landscape pattern, based on the "Theory of Island Biogeography", this paper pertinently constructs three new indices that can be used to measure the urban roof landscape pattern:the minimum ground clearance (MIH), the accessibility index (REAI) and the resistance index (RI). We discuss their ecological significance and value scope, and we also conduct empirical test. Fifthly, by screening the original indices and building new indices, we will conduct correlation test to the selected landscape indices, and finally determine the urban roof landscape pattern index system consisting of 8 indices, such as the average plate margin-area ratio (P) and relative plate area (R). The quantitative calculation result of resistance index (RI) is used to divide the urban roof planning into three levels of green ecological space development areas to gradually build the urban roof ecological plate network. Sixthly, we try to use the "source-sink" theory to study the process in which the urban ecological plate can alleviate the urban air pollution. We conduct quantitative description of source-sink plate and build the accumulative dissipative resistance face model to evaluate the landscape process based on the minimum accumulative resistance model. By building the landscape flow resistance face, we can realize the simulation and calculation of the process in which the ecological plate degraded the air pollutants. Seventhly, by using the accumulative dissipative resistance face model, we can simulate the landscape process of roof ecological network degrading air pollutants under three landscape patterns respectively, which are the current roof greening, the roof greening based on the climate adaptation and resistance index evaluation and planning and the overall roof greening. The result shows that the roof greening landscape patter after optimization has achieved ideal effects in alleviating the air pollution. Finally, based on quantitative calculation and analysis of vegetation non-biological environment factors, the roofs in established area in Chengdu are divided into the three types of superior, classic and extensive roofs. By combining the roof and field investigation, the plant selection standards are stipulated on various aspects such as the plant category, size, root system depth and various resistant indices, and appropriate tree and shrub plant lists will also be recommended. The research result has certain theoretical significance and practical value. |
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