Assessment And Comparison Of Urban Environmental Quality Between Mountainous Cities And Cities On The Flatland

With the advancement of global urbanization,there is a serious conflict between the development of a high degree of urban agglomeration and environmental protection.The urban environmental quality has also been degraded,which create a threat to the sustainable development of the city and the living standards of residents.The evaluation of urban environmental quality and the exploration of its internal driving factors have become the current academic research hotspots.The present research on urban environmental quality mainly focuses on plain cities,and less attention is paid to mountainous cities.Since the development of Western China,the mountainous cities in the area have experienced large-scale urbanization development,but they have also encountered serious environmental problems,such as intensified urban heat island effect,serious water and air pollution,and frequent natural disasters.In view of this,under the guidance of sustainable development theory,quality of life theory and urban environment related theory,this paper establishes a theoretical model of urban environmental quality based on the three dimensions of physical environment,built environment and natural disasters,and selects eight indicators such as normalized vegetation index,air quality index and road network density,The evaluation index system of urban environmental quality is constructed.By using remote sensing image,online map data,ground monitoring data,urban planning data,statistical data and existing research results,this paper evaluates and analyzes the urban environmental quality from two aspects of single index analysis and comprehensive environmental index,using IWD interpolation method,single channel algorithm and other spatial analysis methods,as well as projection pursuit model based on accelerated genetic algorithm.Then it further explores the relationship between the background environment,urban morphology and population distribution and urban environmental quality,and analyzes with typical cases.Finally,it puts forward some planning suggestions to optimize urban environmental quality.The main conclusions are as follows:First,the three-dimensional theoretical model and index evaluation system of urban environmental quality are constructed.Under the natural limitation of the background environment,the three dimensions of physical environment,built environment and natural disasters are interdependent and restrict each other,which together constitute the theoretical model of urban environmental quality.In terms of physical environment,four indicators are selected,including normalized vegetation index(NDVI),air quality index(AQI),road network density and urban heat island intensity.In terms of built environment,three indicators are selected,including industrial land proportion,impervious surface proportion and plot ratio.In terms of natural disasters,the impact of flood on urban environment is mainly considered,and the urban environmental quality evaluation index system is constructed.Second,the single index evaluation results show that the spatial distribution pattern of indicators is obviously affected by urban topography and development pattern.Influenced by the topography of Chongqing and the "polycentricity" development pattern,most of the indicators present a "polycentricity,mosaic" pattern;The plain topography and the early "circle" development pattern lead to the "pie and circle" pattern of Chengdu indicators.Specifically,the vegetation coverage of urban core areas and industrial areas is relatively lower than other areas,and the corresponding impervious surface ratio and urban heat island intensity are higher,such as Yuzui group and Tea Garden group in Chongqing,Longquanyi and Wenjiang District in Chengdu,etc.Jiefangbei,Guanyinqiao,Nanping and other urban core areas in Chongqing and areas within the Third Ring Road of Chengdu have high population concentration,high road network density,serious congestion and acute air pollution.The flood threats in Chongqing mainly come from the rise of water levels in the Yangtze River and Jialing River basins while the urban flooding disaster in Chengdu is even more serious.Third,the spatial distribution results of urban environmental quality index of Chongqing and Chengdu are not the same.The high value areas of Chongqing’s urban environmental quality index are mainly distributed along the two rivers,Renhe,Beibei old city and University City,while the low value areas are mainly distributed in Yuzui,Tea Garden,Xiyong,Dadukou and Tangjiatuo,which have high industrial concentration,showing a “Mosaic” pattern.The high value areas of Chengdu’s urban environmental quality index are mainly distributed in the areas along the Fourth Ring Road and Tianfu New Area in the south while the surrounding industrial intensive areas such as Longquanyi District and Wenjiang District,and the urban environmental quality index within the Third Ring Road are relatively low,showing a "satellite town" pattern.Fourth,the spatial distribution pattern of urban environmental quality is closely related to urban topography,development mode and population distribution.Landscape pattern and plain style are not only valuable resources of urban environment,but also constraints of urban environmental quality.Most of the traffic districts near mountains,rivers,forests and wetlands have high urban environmental quality index.But for mountain cities,mountain barrier may aggravate air pollution,traffic congestion and urban heat island;The lack of natural factors may lead to the development of plain cities,resulting in serious traffic congestion and air pollution“ The spatial structure of " polycentricity " has a significant impact on the urban environmental quality index.The development of Multi Center encourages a good job residence spatial matching within the city,which helps to alleviate traffic congestion,energy consumption and air pollution;However,the sticky development between the main and sub centers of the city may erode the urban green belt and lead to new environmental problems such as landscape fragmentation.There is a significant negative correlation between the population distribution and the urban environmental quality index in Chengdu.The high concentration of population has a serious negative impact on the urban environment;However,the correlation between population distribution and urban environmental quality index is not obvious,which is closely related to the serious industrial pollution of Chongqing as an important industrial town.