**3.2 The unsustainable problems in urban development**

*Environmental Issues and Sustainable Development*

development, according to different regional development potential and the resource environmental carrying capacity, according to the regional division of labor and coordinated development of the principle of overall consideration the future population distribution, economic layout, land use and urbanization pattern, reverse the regional resources excessive development for a long time, the regional

ecological environment has become increasingly serious phenomenon.

**3. Environmental changes and sustainable development of cities**

**3.1 The impact of environmental changes on spatial carrying capacity of cities**

capacity, which determine the degree of urban industrialization and expansion. Understanding the great changes in the spatial and material relationship between human and nature are the key determinant factor of sustainable development [4]. The natural environment can provide humans with the greatest degree of carrying capacity, and the environmental resource basing on which all human economic activities ultimately depend include ecosystems that produce various services [5]. As a result of the interaction between human activities and the natural environment, different natural landscapes, economic patterns, and temporal and spatial dynamic characteristics are produced. It can examine the maximum carrying capacity under the action of man-land relationship, including the upper limit of population, natural resource (water, atmosphere, animals and plants, minerals), and the characteristics of the dynamic changes on the spatial and temporal scales. There has a significant impact on social and economic activities about geographical environment and climatic conditions. China has abundant natural resources, including coal, crude oil, natural gas, pyrite, bauxite, copper, etc., which have promoted the development of manufacturing in coastal and inland area. The difference in factor supply brought by regional resource endowments, which the fundamental reason that determines the continuous development and spatial expansion. Furthermore, the development of urban spatial carrying capacity has gradually shifted to regional division of labor basing on comparative advantages, the man-land relationship shifts to a larger-scale study of the ecological environment, economy and society. The carrying capacity dominated by environmental changes is transformed into a spatial constraint factor as the urban expansion reaches to the certain threshold. The urban spatial carrying capacity under the background of environmental changes focuses on physical geography, resource endowment, and extreme carrying limit. However, when the urban expansion approaches the carrying threshold, the laws of ecological economy such as total withdrawal, structural optimization, and restoration of ecological system functions begin to affect the efficiency of urban economic and social development, and the ecological carrying function is transmitted to the ecological restraint function. At this time, the spatial carrying capacity should be expanded from the original regional scale to the planetary boundary frame below the global scale, emphasizing that the urban economic and social activities should maintain a sufficient safe distance from the threshold of the earth's ecosystem [6]. The concept of planetary boundaries provides a starting point to understand the natural resources and processes on which human sustainable development depends [7], and set up ecological carrying functions of different regions and scales through a global top-down perspective. Based on this, with the development of urban land resources and the expansion of urban space in China, the ecosystem and ecological environment has gradually become the constraining functional bearer of sustainable urban development. Because of negative economic-environmental

Natural resource and environment are the basic elements of urban spatial carrying

**252**

The unsustainable problems in the process of urban development are mainly embodied in the spatial carrying capacity of economic society, population, resource endowments, environmental capacity and various urban service facilities. With the continuous expansion of cities and the rapid growth of population, the carrying capacity on resources and environment has gradually attracted widespread attention. In the process of large-scale industrialization and urbanization in China, the land element, as the basic element of spatial carrying capacity, is the direct element of population, industry and life community of mountains, rivers, forests, fields, lakes and grasses. Due to rapid consumption of land resources, the supply structure and allocation efficiency of land resources show long-term flexibility. China has a large number of resource-based cities dominated by coal, steel, and oil. At the same time, Beijing and Shanghai are also core cities with severe water shortages. In the long run, the structural scarcity of land resources, water resources, and mineral resources will further affect the sustainable development of cities. In the process of urbanization, a large number of populations have been concentrated, especially in rapidly developing global cities in China, where the floating population is huge, consequently a large number of resource consumption, energy consumption, and environmental pollution problems arise. The urban environmental capacity is close to saturation, smog and automobile exhaust pollution, which also common problems in the process of urban development. In addition, the allocation of urban infrastructure and public service facilities are unreasonable, especially the various urban service facilities of large cities have been overloaded, which are also an important issue that restricts the sustainable development.
