| Land resources are regarded not only as the base to maintain the human life and production,but also as an important prerequisite for development of human society.With the growing economic development and urbanization process,some environmental problems,such as reduction of cultivated land,shortage of water resources,environmental pollution,are increasingly,so that the actual land carrying capacity for a number of cities have been on the verge of or beyond its reasonable level.Therefore,it is very significant to study land comprehensive carrying capacity in the process of ensuring the land sustainable use.Furthermore,the study of land comprehensive carrying capacity,which is also considered as an important prerequisite and reference for urban land sustainable development planning,has become a hot issue.In this paper,combined with related theories involving sustainable development,system science,resources scarcity,land comprehensive carrying security,etc.the status quo and future trend of the land comprehensive carrying capacity have been evaluated and predicted.First of all,theories of land comprehensive carrying capacity were systematically studied,including the definition of concept boundaries,research progress in domestic and overseas,existing problems and tasks,etc.;while the evaluation methods of land comprehensive carrying capacity were also in-depth discussed.Based on the preparation above,combined with actual status of land use in Xi'an city,according to different carrying objects the system of land comprehensive carrying capacity was classified as four subsystems of carrying capacity involving land and water resources,ecological environment,economic technology,as well as social development.Furthermore,the evaluation index system was scientifically established by the selection of appropriate evaluation indicators,and then the land comprehensive carrying capacity in Xi'an city from 1994 to 2013 was evaluated.Secondly,a dynamic simulation model of land comprehensive carrying capacity in Xi'an was built on the basis of strict compliance with the model building principles of system dynamics.Moreover,five dynamic simulation schemes,such as status-continuous scheme,economic priority scheme,resource-intensive scheme,environmental protection scheme,and coordinate development scheme,have been designed and optimized by utilizing system dynamics software VENSIM DSS 5.8.After comparison and selection of schemes,the most optimal scheme,which could predict the future trend of land comprehensive carrying capacity in Xi'an city,has been obtained.Finally,based on analyzing the current land use patterns in Xi'an city and the influences of different policy,measures and recommendations to enhance its land comprehensive carrying capacity and to achieve its sustainable land use were proposed.The main contents and innovations of this paper are showed in following three aspects:Firstly,in this paper,the subject and object of land carrying capacity have been expanded by focusing on the land comprehensive carrying capacity of urban areas.Due to the complexity of urban system,the study of land comprehensive carrying capacity should be systematic,the carrying subjects should be broadened from a single land use type in the past to more types,including arable land,other agricultural land and urban construction land etc..In the meantime,land carrying objects should be also expanded from the previous single element,which mainly emphasized on grain production and population scale,into all aspects of urban social and economic development.Moreover,the impacts of soil and water resources utilization and ecological environment factors on urban land carrying capacity have been particularly taken into account,in order to conduct a multi-dimensional,comprehensive and detailed analysis,which proposed a new research direction for domestic researches.Secondly,the comprehensive carrying capacity of urban land has been evaluated and predicted with dynamic and developmental perspective.The existing studies of land carrying capacity,which mainly focused on evaluating the current situation of land comprehensive carrying capacity by static analysis,often lacked to predict its future development trend and ignored the fluidity and feedback of the system.In this paper,with the principle of sustainable development,the dynamic characteristic of land comprehensive carrying capacity system and the liquidity of its components have been paid more attention.Furthermore,taking into account the affects of different policies,a system dynamics model with urban areas as the main object has been established by using the viewpoint of system science and relying on software VENSIM,so that the future development trend of the land comprehensive carrying capacity in the study area could be more accurately observed by the dynamic simulation predicting and optimal selection of programs.And then countermeasures in line with the requirements of land sustainable use and urban sustainable development could be proposed and new areas of system dynamics research have been explored.Thirdly,in this paper,evaluation and prediction will be combined with the identical evaluation index system and calculation method to establish a more complete and scientific study method of land comprehensive carrying capacity.Above all,the existing studies stressed mostly either on evaluating the current situation or on predicting the future trend of land comprehensive carrying capacity,rather than on the both aspects.The simulation predicted results of this paper have been substituted into the calculation method of status assessment to synthesize the evaluation and prediction for clearly showing the status of land comprehensive carrying capacity in different historical stages of the study area as well as for making research results more unity and integrity.Moreover,the methods of the land carrying capacity in current studies mostly adopted AHP,Delphi,etc.,which are more subjective and difficult to objectively reflect the state of land comprehensive carrying capacity in the study area.In this paper,mean square deviation decision method and system dynamics model were combined to establish a more comprehensive feedback relationship,so that assessment and prediction of target would be more scientific and effective.In addition,since the impacts of each subsystem on land comprehensive carrying capacity were not only a simple summation or averaging,but also comprised by influencing with each other and joint coupling.In order to consider both practicality and rationality and to make the evaluation results more accurately,the land comprehensive carrying capacity has been confirmed by weight values of each subsystem in the model in this paper according to the actual situation of the study area,rather than by taking the average of subsystems in the past.Fourthly,countermeasures could be more targeted by separately proposing solutions from the specific problems of each subsystem.Measures and recommendations of previous studies that focused generally on overall view were more general,broad,and absent of specific.This paper proposed according sustainable development strategies respectively from four aspects,such as land and water resources,ecological environment,economic technology and social development,based on analyzing the status patterns of land comprehensive carrying capacity in Xi'an city.Meanwhile,according to prediction results of simulation schemes,the land carrying potential under future different development schemes in Xi'an were separately analyzed from the perspective of the population size and economic scale combined with different policy factors,so that the feasibility of the proposed countermeasures could be improved.In this paper,five simulation schemes have been set to predict future trends of land comprehensive carrying capacity in Xi'an city.The empirical results show that,compared with other schemes,coordinated development scheme is the most reasonable development scheme.In this scheme,the land comprehensive carrying capacity of Xi'an city will reach 0.9091 in 2025,which will approach to 1 and be on the highest level.However,the carrying capacity of soil and water resources will arrive at 0.7872,between 0.6 and 0.8,only on a high level,which indicates that the future land use in Xi'an city should focus on improving resource utilization,appropriately control the scale of urban expansion,especially that of construction land,and make a more rational urban development plan,in order to enhance its carrying capacity of soil and water resources as well as that of social development;It should also vigorously improve the urban ecological environment,increase urban green space,forest and other ecological land area,to intensify its carrying capacity of ecological environment.Through the continuous optimization of subsystem carrying capacity,the land comprehensive capacity of Xi'an city would be upgraded,which will be an important way to achieve sustainable use of urban land and future urban sustainable development. |
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