Research On Urban Growth And Scenario-based Simulation Upon Land Use Change In Xi’an

With accelerating urbanization,cities in China have experienced rapid expansion.Such an extensive urbanization mode brought a series of ecological,environmental and socio-economic problems as:environment contamination,ecology destruction,farmland decrease,food safety and hollow village and so on.Under the strategic background of promoting new urbanization and building the plan of territorial development on whole area and all factors,new requirements are put forward for urban growth management.The research will be focused on exploring how to come to the trade-off of urban expansion,ecological function and cultivated land conservation,reasonably optimize the spatial pattern of urban,agricultural and ecological security through scientifically predicting the evolution of future urban under land use strategies.According to the results of scenario-based model simulation,demarcating scientific and reasonable urban growth boundary and formulating the corresponding control measures are of great practical and theoretical significance to build a sustainable urban development through promoting the new urbanization and rural-urban transformation.This study first elaborates the related theory and research on land use change,farmland and ecological land conservation and urban spatial growth at home and abroad,and finds the key point of this study.The core issues of the research are set up based upon theoretical analysis,and then framework system and research strategy for urban growth research is built in Xi’an.In this study,this research will conclude as follows:(1)Systematic study on the landscape pattern and land use structure change of Xi’an land use in the past 35 years reveal that under rapid urbanization land change is dominated by farmland decrease rapidly and built-up land increase rapidly,showing an obvious linkage between farmland decrease and construction land increase in past 35years.The spatio-temporal coupling research of farmland,rural built-up land and urban built-up land show that 87%of newly urbanized land are transformed from farmland and rural built-up land,with farmland account for 60%and rural built-up land for 27%.However,rural built-up land per Capita is increasing sharply with rural built-up land per Capita 223.98m~2 and urban built-up land per Capita 75.24m~2.Coordinating the urban-rural areas will play an important role in the future urban growth with reducing encroachment upon farmland and other natural resource land.According to the analysis of spatial topology Xi’an has experienced in the way of infilling,extension and leaping since 1980,but new urban built-up land has increased rapidly since 2010,leaping expansion has been more obvious in spatial configuration.Overall,urban expansion still appears relatively dispersed,which evolve from agglomeration to radial expansion.(2)Logistic Regression Model under spatial heterogeneity is established to analyze and screen systematically the driving factors of urbanization,then set up the potential layer of urban growth simulation for FUTURES model.The result shows that there are6 major spatial determinants for urban growth under urban-rural gradient,including:2positive correlated variable(road density and planning)and 4 negative correlated variable(distance to(sub)center,distance to highway,travel time cost and slope).Besides,regression analysis shows that intercepts indicates urbanization suitability on county level in order:three urban districts(Xincheng,Beilin,Lianhu),suburban districts(Weiyang,Yanta,Changan),Yanliang and Gaoling,but Baqiao and Lintong slower because of large forest and grassland coverage.(3)FUTURES as a model of landscape pattern evolution effective simulation at cell level,is introduced to predict urban spatio-temporal growth.Parameterizing and calibrating the model is conducted for input and controll parameters,to make it more suitable for urban growth simulation in China.Especially parameterization from the perspective of new patch quantification and location is conducted to make model running indefinitely approach real growth on cell-level,which conclude that patch compactness,discount and discount range for model is 0.5,0.3 and 0.05,respectively.Based upon sub-models extension interfaces and local land use strategies,weight scheme parameter analysis is firstly introduced to adjust PGA potential layer.The results display when scheme parameter is 0.6,which will come to the tradeoff between rural built-up urbanized area conversion and landscape fragmentation.Thus weight scheme of stimulus rural-urban conversion be introduced in scenarios analysis and urban growth boundary demarcation.(4)For the multi-object land use strategies of encouraging infilling expansion,rural built-up land conversion to urban areas and constructing livable environment,four independent and four combined scenarios are set up and analyzed based upon FUTURES model extension interface.Taking the elements of ecology,basic farmland,water body and history relics site as rigid constraints for urban growth,urban growth boundary is demarcated and analyzed through cell dynamic model FUTURES,which realize the coordination of urban expansion demand,ecological conservation,historical protection and food safety.Under the combination of livable environment,infilling and stimulus rural built-up land transformation to scenarios,the simulation result shows there are 111 patches of urban area in Xi’an for 2030,occupying 102.2km~2farmland and promoting 235.3km~2 rural built-up land urbanized with central urban patch accounting for 68.7%of the total area.Due to the dispersive spatial configuration of rural built-up land,newly urbanized area is seriously fragmented.Therefore,there occur more independent urban boundaries,connected by farmland and ecology land under such three scenarios combination.Under livable environment and infilling scenario combination,the simulation result shows that there are 33 patches of urban area in Xi’an for 2030,occupying 259.2km~2of farmland and promoting 76.4km~2rural built-up land urbanized with central urban patch accounting for 71.8%of the total urban area.Correspondingly,there are less independent boundaries and takes on concentrated extension around urban center.(5)According to urban growth boundary analysis,strategy from traffic orientation plan guideline is put forward including 15km urban circle around urban center and 3km multi-group circle around group center to avoid urban expansion and encourage multi-center development.Urban growth boundary and strategy from scenario-based simulation is helpful to analyze comprehensive conclusion from rural-urban transformation,farmland conservation and urban spatial re-configuration.Urban growth boundary and strategies represents comprehensive attributes of spatial and policy elements,such as social economic development demand,ecology conservation and food security under corresponding scenarios setting.