| Against the backdrop of the continuous acceleration of urbanization,cities are expanding and evolving under the impact of rapid industrialization and economic globalization.While driving regional economic growth and social development,urbanization issues such as loose urban form,reduced land use efficiency,encroachment on ecological and agricultural spaces are becoming increasingly prominent.To solve urban problems such as urban"sprawl",urban development is facing a transformation from extensive outward expansion to intensive inward development.The delimitation of urban growth boundaries is one of the core elements of national spatial planning,and is also a key and difficult point in the delineation of the"Three Red Lines",and as one of the technical means and policy measures for coordinated management of national land space,it is an effective tool to optimize urban structure and promote intensive and efficient use of urban land.Xi’an,as a key city in the"Belt and Road"strategy,is still in the rapid development stage of urbanization.Delimiting its urban growth boundary is of great significance for controlling the growth scale of urban space and alleviating conflicts between urban space expansion and resource and environmental protection.This article focuses on Xi’an as the research area,and uses Landsat5 and Landsat8remote sensing images from 1990,2000,2010,and 2020 to obtain four-phase land use data through interpretation.Based on the distance-weighted aggregation density method,the non-permeable surface density is calculated to extract the boundary of the built-up area of Xi’an.On this basis,GIS spatial analysis methods are used to analyze the spatiotemporal evolution characteristics of urban spatial growth and discover the problems of urban expansion.Based on the ecological sensitivity and land suitability combined with the rigid boundary constraint method,as well as the elastic scale prediction growth method based on the CA-Markov model,the rigid and elastic boundaries of urban growth are respectively delineated,and the comprehensive boundary of urban growth is determined using the coupling model-based comprehensive method.In order to further promote the intensive development of urban land use and coordinate the relationship between protection and development,zoning optimization measures and control suggestions for urban growth are proposed for the study area.The main research content and conclusions are as follows:(1)Study on the spatial growth changes of Xi’an city.By analyzing the changes in land use and the spatial-temporal characteristics of urban spatial growth,problems in the growth of the city boundary were identified.The land use type with the most changes in the study area was farmland,and the expansion of the built-up area was mainly derived from the transformation of farmland.Since 2000,the built-up area of Xi’an city has been expanding rapidly,and the urban spatial form has been expanding significantly in different stages in the north,northwest,west,southwest,and south directions.After 2000,the shape of the built-up area tended to expand in all directions in a coordinated manner,the overall compactness of the built-up area was low,the land use efficiency of the city was significantly reduced,and the overall development of the city showed a significant sprawling trend.(2)Delimitation of the rigid boundary for urban growth in Xi’an.Considering both"ecological constraints"and"land suitability",methods of ecological sensitivity evaluation and land suitability evaluation are respectively used to define different degrees of sensitivity and suitability zones.Based on this,control lines such as basic farmland protection areas are overlaid to delimit the rigid boundary for urban growth.The rigid area for urban growth in Xi’an is determined to be 1462.55 km~2,accounting for 14.48%of the entire study area.This aims to establish the"ecological security baseline"for future urban construction and limit the scope of construction land beyond its constraints.(3)Delimitation of the elastic boundary for urban growth in Xi’an.From the perspective of predicting land use scale,combined with the conversion rules between various types of land use obtained from the interpretation of multi-temporal land use data,four types of urban growth influencing factors were introduced to construct the corresponding CA-Markov model,simulating and predicting the trend of land use change in 2035.At the same time,the elastic boundary for urban growth was defined based on the future development scale of urban construction land.The results show that in the accuracy verification of the simulation results,the Kappa coefficient of the simulation results in 2020 is 0.91>0.75,which was considered to meet the prediction requirements.The subsequent prediction results showed that the total scale of urban construction land in various central towns is expected to reach 1027.57 km~2 in 2035,and this is taken as the elastic development range for urban growth.(4)Delimitation of comprehensive boundary for urban growth in Xi’an.By coupling and modifying the urban growth rigid boundary with the elastic boundary,the comprehensive boundary for urban growth in Xi’an is determined,the area within the boundary range is 865.89 km~2.Based on the spatial relationship between each boundary,the layout of urban growth in Xi’an is optimized and controlled.Targeted recommendations are also proposed to provide reference for achieving the coordinated balance between spatial ecological security and urban growth in the Xi’an region. |
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