Defining Of Urban Growth Boundaries Under The Constraints Of Ecological And Food Safety Bottom-lines

The large-scale expansion of urban land in China has occupied a large area of ecological and agricultural land,which poses a great threat to regional ecological security and food security.The ecological redline(eco-redline)and basic farmland are the strictest bottom-lines of ecological and food security,respectively.The urban growth boundary(UGB)is the important tool of controlling the disorderly expansion of urban land.Guided by the bottom-line thinking,exploring the delimitation method of UGB under the constraints of ecological and food safety bottom lines is of great significance for the coordination between the guidance of urban expansion and the ensurance of ecological and food security.The current research perspective on the delimitation of UGB is relatively single,resulting in the increasingly serious contradiction between urban development,ecological and cultivated land protection.Therefore,on the basis of analyzing the connotation of UGB combined with the threshold theory,this study first analyzed the evolution law of land use pattern in Wuhan and tested the driving factors of land use change.Then,the importance of ecosystem services(ESs)and ecological sensitivity in Wuhan was evaluated,and the evaluation results were integrated for the delimiting of different levels of eco-redlines.Thirdly,the comprehensive quality evaluation system of cultivated land in Wuhan was constructed,and the basic farmland was delimited.Finally,took basic farmland and different levels of eco-redline as constraints,this study delimited the insurmountable rigid UGB and elastic UGB which can be adjusted appropriately according to the urban development needs in a certain period of Wuhan.The research resulted that:(1)During the study period,the land use pattern in Wuhan gradual changed sharply.The area of construction land increased continuously,while the area of other land decreased.Among which,the area of cultivated land decreased the most,and the reduced cultivated land was mainly transferred out to construction land.(2)Based on the evaluation results of ESs and comprehensive ecological sensitivity,the I-class and II-class eco-redlines of Wuhan were respectively delineated,with an area of 1821.15 km~2 and 616.81 km,respectively.The eco-redlines are mainly constructed by rivers,lakes and forest land.(3)Combined with the planning documents of Wuhan government,the cultivated land with the best comprehensive quality was defined to the basic farmland,with an area of 2434.36 km~2.(4)Superposed the I-class eco-redline with the basic farmland to format the forbidden construction area,the rigid UGB was delimited with an area of 2700.41 km~2.Took the I-class eco-redline,II-class eco-redline and basic farmland as the constraint conditions,and then simulated the land use change condition of Wuhan through the FLUS model,the elastic UGBs of Wuhan in 2025 and 2035 were delimited with an area of 1537.41 km~2,1909.67 km~2,respectively.The study shows that: Taking I-class eco-redline and basic farmland as the bottomline constraints of ecological and cultivated land protection,delimiting the rigid UGB should be the largest and non-adjusted boundary for urban development and construction.Taking the I-class eco-redlines,II-class eco-redlines and basic farmland as strict constraints,simulating the future land use change of Wuhan and delimiting the shortterm and long-term elastic UGBs should be taken as the guidance of urban development and construction.the elastic UGBs can be adjusted appropriately according to the urban development needs in different periods.