Spatiotemporal Heterogeneity Of Urban Expansion In New Metropolitan Suburb

Since the reform and opening up,China has made considerable progress in economic and social aspects.Urbanization is pressing ahead quickly in China and it is considered an important theme which will impact human development in the 21st century,and sparks widespread concern.With the influence of economic globalization and development impulse of local government caused by decentralization,urban fringe especially the New Metropolitan Suburb,becomes the key region of urban development and new economic growth pole.The urban expansion in the New Metropolitan Suburb shows new characteristics.Therefore,it's necessary to study its spatiotemporal heterogeneity of process,mechanism in order to reveal the dynamic laws of urban expansion under the background of suburbanization,and provide useful reference for urban planning management and development decisions.Influenced by the continuous diffusion of production factors from Nanjing central city,there is rapid development of economy and urbanization in Jiangning District,so it could serve as a typical district to study urban expansion in the New Metropolitan Suburbs.The paper systematically reviews and combeds the related theories development and empirical research progress of urban expansion;and theoretical analysis is given to the spatiotemporal heterogeneity of urban expansion in the New Metropolitan Suburb from dynamic process and driving mechanism in the context of economic transformation.On this basis,the paper builds a research framework of urban expansion in the study area:"overall situation,process and pattern,driving mechanism,forecast and control".The major contents include:1)The overall situation of urban expansion in the context of economic transformation.Through global indexes which show the urban expansion rate,direction and morphological characteristics,this paper grasps the overall situation of urban expansion,and explores the influential factors for aggregate growth of urban land based on the context of China's economic transformation.2)The spatiotemporal heterogeneity of urban expansion process and pattern.On the basis of the overall analysis,the paper continues to analyze the spatiotemporal heterogeneity of urban expansion process and pattern from different perspectives,including urban land expansion distribution,form and gradient.3)The spatiotemporal heterogeneity of driving mechanism of urban expansion.With the help of GIS spatial modeling technology,the paper analyzes the spatiotemporal heterogeneity of driving mechanism of urban expansion,in order to excavate the main control factors in different expansion stages and corresponding expansion forms,and further analyze the spatial nonstationarity of driving effect of the factors.4)The future spatiotemporal pattern and control of urban expansion.Coupling SLEUTH model and GWLR model,this paper forecasts the future urban expansion in the study area,analyzes its spatial pattern's evolutionary features,and proposes some control measures of future urban land development.The main results and findings are as follows:(1)During the study period(1986-2010),Jiangning District expanded rapidly,its urban land area increased by 6.68 times,showing strong development momentum.The urban expansion in the study area has experienced three stages including slow expansion(1986-1992),accelerated expansion(1992-1999)and rapid expansion(1999-2010);the spatial structure has changed from a "single center" to "one center,triple-core,and multi-group".The expansion forms include edge-expansion type,outlying type and infilling type.In the slow expansion and accelerated expansion stages,urban expansion rate is slow and presents spatial characteristic of anisotropy;edge-expansion is the dominant type while outlying type is also obvious.In the rapid expansion stage,under the guide of development zone and new town construction,urban expansion rate speeds up and favors the southwest direction,edge-expansion type is still dominant while infilling type accounts for a certain proportion which gradually increases.The landscape pattern of urban-rural gradient belt has changed dramatically,which manifests multi-center pattern,and urban expansion is constrained by cultivated land protection,land index,ecological environment,etc.(2)In the slow and accelerated expansion stages(1986-1999),the pull of traffic network and reproduction of urban patches are the important driving forces of urban expansion in the study area.In these two stages,in addition to minor roads and urban patches,infilling expansion and edge-expansion expansion are also respectively affected by city and town centers,major roads.Outlying expansion is mainly affected by traffic accessibility.In the rapid expansion stage(1999-2010),the industrial agglomeration effect gradually increased;the government-led construction of development zone and the "top-down" area propulsion is the dominant mode of urban expansion.In addition,the promotion of urban internal traffic and agglomeration effect of core city is also obvious.During this stage,the development zones,minor roads and urban patches are the main controlling factors of infilling expansion and edge expansion;the driving effects of subway stations and town centers to the infilling expansion also cannot be ignored.Meanwhile,outlying expansion is mainly affected by town centers and spatial planning.(3)The driving mechanism of urban expansion has spatial heterogeneity,compared to SELR model,GWLR model is better suited to explore the spatial nonstationarity of the effect of driving factors.The development zones have greater promotion to the land urbanization of surrounding area than other regions,reflecting the urban expansion characteristics of agglomeration and area propulsion in the study area.Among them,the expansion of Binjiang Development Zone and Konggang Industrial Park in the outer suburb is caused by a large demand of industrial land while the expansion of Jiangning Science Park in the near suburb is closely related to the university new campus construction.Minor roads have strong promotion to the urban expansion of central part of the study area,which suggests the strategy of transportation ahead plays a crucial role in the regional land development.Under the influence of industrial agglomeration effect,reproduction of urban patches has the strongest effect in Binjiang Development Zone,whose urban expansion shows the continuity.Subway,as a new spatial element of the study area,changes the regional urban land use significantly,promotes the land urbanization along the subway line effectively,and stretches the development framework of the city.(4)Restricted by topographical slope,farmland conversion and ecological protection polices,future urban expansion rate in the study area will gradually decline.The complexity of urban form will decrease and future urban land development will tend to be more compact.As for the local characteristics,the hot zone of future urban expansion will change.From 2010 to 2020,the hot zones and secondary hot zones will distribute in the form of "one core city,four sub-cities,and two loops";from 2020 to 2030,the hot zones and secondary hot zones will shift outward,and the overall layout will be divergent like an oblique Z letter,the core-periphery effect of urban development will become obvious.In order to effectively control urban expansion and improve the land use efficiency,the government should focus on defining urban growth boundary,integrating internal traffic,controlling the key development sites,promoting more intensive land utilization,etc.