Modelling the Carrying Capacity of Urban Ecosystem

The urban ecosystem is a Social-Economic-Natural Complex consisting of human beings and their surrounding. Because resources and environmental quality are crucial to the existence and development of an urban ecosystem, the development of an urban ecosystem is necessarily built on the basis of interactions among environmental carrying capacity (ECC), resource carrying capacity (RCC) and social-economic development capacity (SEDC). A single component's capacity should not be studied without considering the integrity of the whole system. In this paper, the concept of 'Compound carrying capacity' (CCC) is introduced and studied as an index of the interactions among ECC, RCC and SEDC, as a basis for meeting the challenges of urban sustainable development and eco-city building. Using this index, it is discussed in both theory fundamentals and quantitative models how these three kinds of capacity function to sustain the urban ecosystem. The concept of CCC is introduced to improve the comprehensive understanding of this system's structure and functions. Compared with traditional concepts, the CCC of the urban ecosystem includes the ability to develop and thus is characterized by being more dynamic. This dynamism shows in the ability of cities to respond when put under pressure. Clearly, this dynamic is not endless, both environmental, resource and social-economic development capacities have limits. A comparative study of urban ecosystems and the human immune systems shows that both systems have similar features. Thus, the CCC model is discussed in this paper in light of the biology immunity theory. In this it is assumed that the urban ecosystem is the material input and its main function is to offer eco-services. The extent of these services is dependent on both the intrinsic carrying capacity and the acquired carrying capacity of the urban ecosystem. The methodology for both calculation and adjustment mechanism of the CCC is outlined, with reference to the urban ecosystem health index and evaluation models of sustainable development. This quantitative model of CCC includes five parts: the intrinsic carrying capacity, the acquired carrying capacity, the integration of both basic and acquired carrying capacity, the absolute carrying capacity and the comparative carrying capacity of the urban ecosystem. In addition, a case study in Guangzhou city of China is described. Employing the CCC model, the complex carrying capacity of Guangzhou City was evaluated. This study showed that the CCC and pressure in Guangzhou were relatively balanced. The urban ecosystem was basically healthy, but in some parts, adjustments should be made in terms of economic activities and ecological restorations.