Urban Metabolism: A Review of Current Knowledge and Directions for Future Study.

During the 50 years since the concept of urban metabolism was proposed, this field of research has evolved slowly. On the basis of an analogy with an organism's metabolism, the concept of urban metabolism has become an effective method to evaluate the flows of energy and materials within an urban system, thereby providing insights into the system's sustainability and the severity of urban problems such as excessive social, community, and household metabolism at scales ranging from global to local. Researchers have improved this approach, evolving from models of linear to cyclic processes and then to network models. Researchers account for flows of energy and materials, ecological footprints, inputs and outputs, and the characteristics of the system's ecological network. However, the practical methods of analysis need to be improved. Future analysis should focus on establishing a multilevel, unified, and standardized system of categories to support the creation of consistent inventory databases; it should also seek to improve the methods used in the analysis to provide standards and guidance that will help governments to achieve sustainable development. Finally, researchers must improve the ability to provide spatially explicit analyses that facilitate the task of applying research results to guide practical decision-support.