The Urbanization Process Of The Loess Plateau And Its Ecological Environment Response

The regional ecological environment problems brought by the development of global urbanization have been serious increasingly since the 21st century.Governments have listed urbanization and regional ecological security as important components of their national security strategies and incorporated them into their national overall development strategies.Studying the coupling relationship between urbanization and global changes and regional resources and environment from global sustainable development,revealing the impact of urbanization process on regional ecological environment changes at different spatial scales,and improving the adaptive capacity of cities coping with global changes have become the frontier domains of earth system science.In the transitional development stages of urbanization from "quantity growth" to "quality improvement",the coupling stress relationship between urbanization and ecological environment in urban agglomerations,especially eastern megacities,have attracted the attention of academics and political circles.While studies on the urbanization process and its ecological environment impact of the west typical ecological fragile areas remain weak.As key levels of China's urbanization development and important nodes of the urban system,counties are the key carriers of China's new urbanization and ecological civilization construction in the new era.Therefore,by studying the urbanization process of counties and the ecological environment responses,identifying the spatial-temporal laws of urbanization on the ecological environment and promoting the coordinated development of urbanization,and ecological environment have become practical needs to break the contradiction between Chinese urbanization development in a new era and ecological environment protection in accordance with national strategy needs.The Loess Plateau region is a significant part of ecological security strategic pattern with the main body of "Two Screens and Three Belts" in China and plays an extremely important role in ensuring ecological security in the middle and lower reaches of the Yellow River and farming-grazing transitional belt.Since the implementation of China's Western Development Strategy,regional urbanization construction have attained great achievements and formed the Guanzhong Plain urban agglomeration which is a national urban agglomeration steadily-constructed,and guided and cultivated urban agglomerations of Jinzhong,Lanxi,Hubaoe'yu(Hohhot,Baotou,Erdos and Yulin)and Ningxia Yanhuang(ten cities along the Yellow River in Ningxia Hui Autonomous Region)by the country.However,with the high-speed urbanization process,the high-intensity urban and rural construction has exerted tremendous pressure on the fragile ecological environment of the Loess Plateau.In the process of implementing the new urbanization strategy and the rural revitalization strategy,how to promote urban and rural construction and ecological environmental protection,to continuously meet the growing needs of the better living and good ecological environment of the residents,and to achieve a win-win situation for urbanization development and ecological environmental protection are reality needs of the Loess Plateau achieving high-quality development.To this end,this study,from the comprehensive geographical perspective,takes the theory of human-land relationship territorial system theory,resource and environmental carrying capacity theory and ecosystem service theory as the guide,builds an urbanized ecological environment supply and demand balance theory,and integrates the analytical methods of geoscience,ecological science and environmental science.The research studied the temporal-spatial urbanization process and the ecological environment response of 341 counties(districts)in the Loess Plateau from 1990 to 2015 and proposed the modes and strategies for the coordinated development of urbanization and ecological environment in the Loess Plateau.The research shows:(1)There are multi-dimensional characteristics of the ecological environment impact of urbanization process.The ecological environment supply and demand balance theory of urbanization is an important basic theory to reveal the ecological environment response of urbanization.The urbanization process is a depiction of the urbanization in a specific period and a specific geographical area,and is a change process of urban socio-economic phenomenon projected on geospatial space.The problems of environmental pollution,ecological damage and resource depletion caused by population agglomeration,spatial expansion,and social and economic development in urbanization process are the concrete manifestations of the ecological environment impact in the urbanization process.Ecological environment supply and demand balance theories of the urbanization are the integration,deepening and summarization of multiple theories such as sustainable development theory,ecosystem service theory and resource environment bearing capacity theory.In the urbanization process,the ecological environment system provides the necessary ecological products for urbanization development,and supports the sustained and rapid development of urbanization.The urbanization puts demand for regional ecological products through population increase,industrial agglomeration and spatial expansion.The dynamic balance of ecological environment supply and demand in the process of urbanization are achieved through their mutual influence and interaction.(2)The spatial and temporal changes of urbanization level and the regional differences in the counties of the Loess Plateau are evidently.The natural geographical environment and the humanistic economic foundation are important factors influencing the urbanization development.From 1990 to 2015,the county urbanization progressed from the slow growth stage to the accelerated development stage.The spatial pattern of urbanization changed from low-level unbalanced development to a high-level balanced relatively development.The growth rate of urbanization rate features the transformation of low-growth(high-growth)counties into high-growth(low-growth)counties.Geospatially speaking,it presents a macroscopic pattern of high in the east and middle and low in the west.The factors affecting the regional differentiation of urbanization in descending order are:non-agricultural industry output value,per capita total retail sales of social consumer goods,per capita food production,population density,minimum travel time to central cities,per capita disposable income of urban residents,per capita gross regional product,urban investment in fixed assets,per capita net income of peasants,per capita financial expenditure,average distance to national and provincial trunks,topographic relief,mean altitude,annual average temperature,annual average precipitation.The explanatory power of the urbanization level will be significantly improved after the interaction of any two of the 15 factors,which is characterized by nonlinear enhancement or bilinear enhancement.Among them,the interactions between the non-agricultural industry output value and other factors are at higher levels.(3)The intensity of urbanization in the counties of the Loess Plateau has changed significantly,which has a profound impact on the ecological environmental factors such as the surface temperature,the vegetation coverage and the carbon fixation and the oxygen release of vegetation.From 1992 to 2015,the urbanization intensity of the Loess Plateau gradually increased,and the space expansion of urbanization was obvious.Geospatially speaking,it presents obviously the spatial characteristics of a prominent "Core-Periphery" expansion mode and the coexistence of internal filling and external expansion.The surface temperature in the core areas of urbanization is generally higher than that outside the core area.The surface temperature differences between the core area and the peripheral area,and between the core area and that outside the core area both show an inverted "U" change trend by rising first and then decreasing.The urban heat islands and non-heat islands in the whole district present relatively stable distribution patterns.The heat islands are mainly distributed in construction land and bare land areas,and the non-heat islands are mainly distributed in forest land,grassland and water areas.The urban light intensity shows a synchronous upward trend with the vegetation coverage and the ecological value,which is the leading trend of urbanization and ecological environment evolution of counties in the Loess Plateau.However,the NDVI and ecological values of counties in the Guanzhong Plain urban agglomeration,the Jinzhong urban agglomeration,the Hubaoe'yu urban agglomeration and the Lanxi urban agglomeration,as well as the energy and mineral resources development zones,are significantly reduced even though their light intensities increased significantly.(4)The supply and demand of urban ecosystem services in the counties of the Loess Plateau show clear regularity.The intensity of urbanization is a key factor affecting the supply and demand status of ecological environment in counties,which is diverse in form.The overall quantity of ecosystem service supply in the Loess Plateau shows an "S" change trend by decreasing first then rising and then decreasing,and the demand for ecosystem services presents a "U" change trend which decreases first and then increases.In the 25 years,the counties' ecosystem service in the urbanization process is overall in high supply,and there is little potential to be tapped at this stage.The ratio of supply and demand of ecosystem services shows a spatial pattern of high in the northwest and low in the southeast.The supply rate of ecosystem services in the whole region shows a downward trend.The counties'ecosystem services are generally in surplus,but the supply and demand situation is deteriorating.The greater the urbanization intensity,the more prominent the contradiction between supply and demand of ecosystem services.The region's 341 counties(districts)belong to 19 different supply and demand types.Among them,the number of the counties of middle-stage urbanization with medium-supply and medium-demand ecological services is the largest,accounting for 22.29%;the second is the counties of middle-stage urbanization with low-supply and medium-demand ecological services,accounting for 13.20%;and the counties of early-stage urbanization with high-supply and medium-demand ecological services and counties of late urbanization with high-supply and low-demand ecological services are the lowest,both accounting for only 0.29%.(5)The county urbanization and the optimal regulation of the ecological environment in the Loess Plateau are the interaction processes among the supply side of the counties' ecological environment,the demand side of the urbanization development and the external environment change control.To realize the intensive use of resources and environment and the virtuous circle of ecosystems in the urbanization process is the overall goal of the coordinated development of urbanization and ecological environment in the counties of the Loess Plateau.The supply-side regulation focuses on optimizing the ecosystem structure and improving the quantity and quality of urban ecosystem services.The demand-side regulation focuses on optimizing urban spatial patterns and improving the level of resource intensive utilization.The regulation of external environmental changes is mainly to deal with the uncertainties caused by global changes in the county urbanization process and the supply and demand pattern of ecosystem services.To ensure the steady improvement of urbanization level,the effective supply of ecosystem services and the reasonable and appropriate demand for ecosystem services of counties,the moderate urbanization model,the intensive urbanization model,the green urbanization model,the shared urbanization model and the open urbanization model could be implemented by actively optimizing urban spatial layout,building new urban systems,innovating natural resource allocation methods,building intensive low-carbon towns,accelerating industrial restructuring,promoting economic transformation and upgrading,deepening policy and institutional reform,promoting urban-rural integration,strengthening ecological environment and ensuring urban ecological security,etc.Accordingly,the healthy,intensive,green,shared and open cities and towns could be established,and the high-quality development and effective protection of the ecological environment in the county urbanization of the Loess Plateau could be achieved in the new era.The innovations of this research are mainly as follows:(1)Constructing the urbanization ecological environment supply and demand balance theory,which is used to guide the ecological environment state response research of county urbanization,and develop the basic theory of the relationship between urbanization and ecological environment;(2)Constructing a "three dimensional evaluation model" consisting of urbanization development stage,ecological environment supply and ecological environment demand,innovating the urbanization supply and demand status and identification method of type judgment;(3)discovering the urbanization presents a spatial pattern of "core-periphery"in the Loess Plateau,and the vegetation green degrees and ecological values are relatively high in the surrounding areas constituted by the urban built-up ares of the plateau sandstorm area and desert areas.It is considered that understanding the relationship between urbanization and ecological environment from a dialectical and systematic perspective is the scientific way of realizing the ecological environment response stage and regional differences of urbanization.(4)Designing the framework of urbanization and ecological environment optimization and regulation,clarifying the ecological environment supply and demand adjustment goals,priorities and directions of the urbanization,and proposing the coordinated development model and strategy of county urbanization and ecological environment in the Loess Plateau.