Research On Spatio-temporal Evolution Evaluation And Optimization Of Green Space In Chengdu-chongqing Urban Agglomeration Under Multi-objective Orientation

With the rapid development of urbanization,the marginal benefits of individual cities have decreased significantly,and the urban agglomeration model has become one of the important planning forms to enhance the competitiveness of cities in the world.As an important intersection center of China’s "two horizontal and three vertical" urbanization strategic pattern,Chengdu-Chongqing urban agglomeration is an important platform for China’s western development,and also an important demonstration area for the country to promote new urbanization.Its green space not only carries the basic needs of ecology,economy,recreation and culture in Chengdu-Chongqing urban agglomeration,but also serves as an overall planning of urban space,tourism and culture in Chengdu-Chongqing urban agglomeration Coordination is an important link between social economic system and natural environment system.In recent years,due to the continuous progress of urbanization and the rapid development of regional economic industry,the shortage of resources and ecological degradation caused by human activities and economic production seriously threaten the sustainable and healthy development of green space,and also restrict the urbanization process of Chengdu-Chongqing urban agglomeration.This study takes the whole area of Chengdu-Chongqing urban agglomeration as the research scope,takes the green space as the main research object,selects four time nodes in 1990,2000,2010 and 2020,and constructs the research framework of "evolution evaluation drive identification scenario simulation optimization improvement".Firstly,the spatial dynamic degree,spatial transfer matrix,landscape pattern index and ecosystem services are used to evaluate the spatial-temporal evolution characteristics of green space in Chengdu-Chongqing urban agglomeration from three aspects of scale stock,spatial pattern and service function,and to clarify the basic problems;Secondly,using OLS,SEM,SLM and GWR to clarify the specific driving factors and driving mechanism of green space structure and service function in Chengdu-Chongqing urban agglomeration;Thirdly,the SD-FLUS scenario prediction model is constructed,and the system dynamics(SD)and future land prediction(Fl US)models are coupled.Combined with the multi-objective scenario constraints of ecological priority,economic development,recreation equity and cultural protection,the storage scale and spatial layout of various types of green space in Chengdu-Chongqing Urban Agglomeration in 2030 are predicted;Then,morphological spatial analysis(MSPA)and minimum cumulative resistance(MCR)model are introduced to identify the power sources and functional corridors,and a multi-functional network optimization layout is constructed;Finally,combined with hot spot analysis(GI *)and bivariate spatial autocorrelation(local Morans ` I)index,the trade-off and collaborative relationship of green space service function of Chengdu-Chongqing urban agglomeration is identified,and the planning control suggestions are put forward.The main conclusions are as follows:(1)Green space stock: two minus four increase,the total decline.During the study period,the total amount of green space decreased by 3741.98 square kilometers,the area of cultivated land and grassland decreased,and the area of forest land,water area,built-up area and unused land increased.The spatial transfer of green space to built-up area is the main transformation process,which mainly occurs in the dual core cities,the areas with dense river network and the peripheral shallow mountain areas.(2)Green spatial pattern: it tends to be fragmented,discrete and complex,and the deterioration of the pattern is increasing year by year.The structure of green space in the middle of urban agglomeration is significantly better than that in the periphery of urban agglomeration.The double core urban green space in the East and west of urban agglomeration has been in a highly fragmented state for a long time,and its ecological environment security and stability are under great pressure.(3)Green space function: the overall service is high outside and low inside,and the whole area is declining,and most of the sub services are declining.Within the time limit of the study,the total value of service function has declined by more than 1.991 billion yuan,with a decline rate of more than 0.55%and a global decline area of more than 90.38%.Moreover,the decline trend has been enhanced in the near ten years from 2010 to 2020,and the ecological resources background of Chengdu-Chongqing urban agglomeration has been obviously interfered and disturbed.(4)Green spatial pattern driving: mainly affected by social and economic factors,the driving intensity rises as a whole,and the driving causes tend to be complex and diversified.Slope is one of the most important natural environmental factors affecting green spatial structure,and the gross value of primary industry and population are the most important socio-economic factors.With the development of green space and urban space,the green space pattern of urban agglomerations is gradually changing from the early development period of urban agglomerations which is mainly driven by natural environmental factors to the high-speed development period dominated by social and economic factors.(5)Driven by green space service: affected by the natural environment and social economy,the former intensity decreases,the core driving factors are slope,temperature,rainfall and NDVI,while the latter intensity increases,and the core driving factors are population density,GDP per unit area and the proportion of primary and secondary industries.During the study period,most of the natural environmental factors maintained relatively high driving intensity in the peripheral shallow hills,but began to decline in the central plain area,and gradually changed into the influencing factors of constraint conditions;Most of the socio-economic factors in the central urban space and shallow mountain areas of most cities have increased intensity,and the impact of human activities on the service function of green space is gradually increasing.(6)Scenario simulation of green space: Design multi-objective scenario constraints of ecological priority,economic development,recreation equity and cultural protection.The prediction results show that in 2030,the green space presents the evolution trend of "one decrease and five increase,one main and multiple secondary,high in the north and low in the south,high in the West and low in the East",that is,the cultivated land is reduced,and the area of other types of green space is increased,The decline of the total amount of green space will be effectively controlled,the blue-green space in most cities will be improved,and the damaged wasteland will be restored;At the same time,the development speed of cities with Chengdu as the main core has increased again.As a core city,the expansion speed of Chongqing has begun to decline,and the development speed of plain cities such as Ziyang and Suining has increased.There is a trend of forming a number of sub core cities.(7)Green space network optimization: Based on the multi-objective collaborative positioning of ecological priority,economic development,recreation equity and cultural protection,build a multifunctional network structure of "one ring and three veins,dual core and multi-point,dual ring network,multi-point and multi corridor".Among them,the ecological function network forms the shallow mountain ecological ring in the peripheral shallow mountain area,and forms three main ecological function veins in the West Longquan Mountain,the East Sichuan fold mountain in the East,and the central intercity expressway;The economic function network gathers a large number of source areas around the dual core cities,and there are also high-level economic nodes in plain areas such as Suining,Ziyang and other new towns;There are a large number of recreational function networks in the periphery of Chengdu and Chongqing,which gather around the dual core cities,and form a dense network space relying on linear blue-green elements such as mountain forest,lakes and rivers;The cultural function network is evenly distributed in the shallow mountains in the south,the folded mountains in the east of Sichuan and the plain river network.(8)Promotion of green space management and control: Based on the relationship identification of trade-off and collaboration,the subsequent optimization management and control approaches of Chengdu-Chongqing urban agglomeration can be divided into structure optimization and bottom line control with structure as the leading goal;To enhance the pattern and strengthen the function with industry as the leading goal;Function oriented stock protection and system control.It is an important way to optimize the green space management and control strategy of Chengdu-Chongqing urban agglomeration to reasonably understand the trade-off and collaborative relationship between the future development of natural system and different functions of different systems.The core innovation of this study is: Based on the perspective of landscape architecture discipline,the theoretical framework of urban agglomeration green space research is constructed,which is "evolution evaluation drive identification scenario simulation optimization promotion",and the green space of Chengdu-Chongqing urban agglomeration is analyzed in detail by integrating multi-disciplinary research methods Evaluation,prediction and optimization.The scale of this study covers urban agglomerations,cities,districts and counties,and units.The research results not only clarify the development characteristics of the spatial-temporal evolution of green space in Chengdu-Chongqing urban agglomerations,but also reveal the influence mechanism of natural environment and social economy on the spatial-temporal evolution of green space in Chengdu-Chongqing Urban Agglomerations,The multifunctional network optimization structure of Chengdu-Chongqing urban agglomeration green space is constructed,which provides a scientific basis for the follow-up development planning of ChengduChongqing urban agglomeration green space,and also provides research ideas for the research of other national urban agglomeration green space.