Characterizing urban metabolic systems with an ecological hierarchy method, Beijing, China

Abstract The resource and environmental issues that are emerging as a result of rapid urban development have made the study of urban metabolism increasingly important. However, past studies on urban metabolism have focused primarily on the system's external characteristics rather than on the internal production and consumption processes. To better understand the underlying mechanisms of urban metabolic processes, we present a method through which one can examine and characterize the production and consumption flows intrinsic to an urban metabolic system. Drawing upon several analytical procedures from ecological network analysis, we applied the method to a case study in Beijing, China. We collected a large body of statistical data and used it to account for the material flows inside Beijing's system from 1998 to 2007, thereby providing a quantitative network model of the system. We found that the paths between different components of Beijing's urban metabolic system remain simple, that there is insufficient cycling, and that the city's lack of internal environmental support capacity forces it to depend heavily on inputs from the external environment. These results suggest that the city needs to develop the reducer (recycling) component of its hierarchy to reduce the double pressure on its internal environment created by demands for resource supply and for absorption and recycling of wastes and other materials. This will help Beijing to achieve more sustainable development.