Urban Growth Boundary Delineation Method Based On Ecological Security Pattern

Since the 1990s,the urbanization has been enhanced rapidly in China.Urban land expansion is one of the most obvious manifestations of the urbanization.With the dramatic increase of urban construction land area,a large number of cultivated land and other types of land will inevitably be occupied by construction land.The phenomenon has disrupted the structure and function of land ecosystem,and destroyed the natural circulation and conversion of energetic contents;leading to the ecological environment is faced with a serious crisis.This kind of crisis is manifested in a series of ecological and environmental problems including ploughing land source contamination,air pollution,water shortage,and declining biodiversity.These problems not only have had impacts on the urban area,but also changed the ecological environment of the rural areas around the city,which seriously restricted and affected the sustainable development of the city.Over making efforts to promote urban economic construction,various research fields pay attention to the methods of promoting the coordinated development between human and nature.Based on the analysis of the spatial and temporal characteristics of urban land expansion,this paper takes Hohhot urban area as the research area to construct an ecological security evolution evaluation model and an ecological vulnerability assessment model.It evaluates the ecological security evolution trend of the study area,and clarifies the interactive mechanism of the urban land expansion and ecological security evolution.Finally,combined with the external constraints and endogenous mechanisms of urban land expansion,this paper delineates the urban growth boundary of the study area in 2025 according to the results acquired by the coupling resistance and driving force simulation on the urban based on the UEER model and the CA-Markov model.The main conclusions are as follows:Firstly,this paper analyzes the spatial and temporal characteristics of urban land expansion in the study area,and the results represent that the urban framework of the study area has been continuously expanded,the rate of land expansion has been accelerating,and the expansion intensity remains a high level,and the urban land is mainly extended between 1990and 2016.Without stability,the external form of the city is becoming less compact,and the urban expansion presents an unreasonable state.Based on the sequential analysis in 2001 and 2010,there is an anisotropy in the intensity and direction of urban land expansion in the four periods.The city's center moved 1819 meters towards south-east,with an offset angle of 20.12°.Secondly,there established an ecological security evaluation system based on the urban land expansion.The results illustrate that from 1990 to2016,the ecological security comprehensive index shows a descending trend from a top level to an average one.In terms of each factor,the security index shows a declining trend on factor,exposure and influence,while it shows a rising trend on response.This paper makes an analysis of the factors on ecological security,and gets the results that urban ecological security can be influenced significantly by such factors as the level of urbanization,the compactness of urban form,the integrity of urban landscape patches,the degree of aggregation,the rational layout of land,and the importance of human response.Thirdly,from the trend of ecological fragile space evolution,the ecological vulnerability of the study area has increased as a whole,and its spatial distribution has increased gradually from the west to the south and the southeast.The main characteristics of ecological fragile spatial changes are regarded as the continuous expansion of severe and extremely fragile areas and the spatial shrinkage of slightly and slightly vulnerable areas.The ecological fragility values descend“from south to north,west to east”.From the perspective of the relationship between land use change and ecological fragility change,provided that the land types remain unchanged,its ecological fragility changes are not significant,and vise versa.The conversion of unused land into forest land and waters will reduce the ecological burden,and the change of other land types into construction land and unused land will increase the ecological burden.Fourthly,the delineation of urban growth boundaries starts from two aspects as the external constraints and endogenous mechanisms of urban expansion.By constructing an integrated ecological security pattern,the rigid growth boundary of land expansion is delineated.The results reveal that the total construction land area within the rigid boundary is 587.1km~2,and the growable area is 129.87km~2.Mainly considering the driving factors such as population,economy and transportation,the endogenous mechanism of urban expansion carries out multi-scenario simulation of urban land expansion in 2025.The results illustrate that the eco-economic program has the highest ecological security index and the most reasonable urban land expansion.Finally,combining the future development of the research area,the urban expansion rigid growth boundary,and the eco-economic expansion plan,this paper delineates the urban growth boundary of the research area in 2025.The results demonstrate that the area within the urban growth boundary of the study area totals 556.41km~2 in 2025,accounting for26.72%of the total area of the study area.There is a construction area of457.23km~2 within the boundary,and the remaining land for construction can be 99.18km~2,which is 30.69km~2 less than the growable area of the predicted construction land based on the ecological security pattern,which can provide land protection for urban land expansion.