Emergy-based Environmental Impact Assessment in Urban Metabolic Process: A Case Study of Beijing, 1999-2006

The urban metabolic process causes impacts on natural capital and human capital, which range from local to global scale. In this study, an emergy-based environmental impact assessment model is designed for the urban metabolic system of Beijing from 1999 to 2006. The model focuses on two main typologies of processes, i.e., production and consumption. The direct and indirect emergy demand was assessed based on airborne and waterborne pollutants dilution patterns, and concepts of Life Cycle Impact Assessment. Results suggest that: (1) nitrogen dioxide and greenhouse gases released by the urban system heavily contribute to both natural and human capital losses evaluated in emergy terms; (2) emissions’ impact, mainly coming from airborne pollutants, with smaller significance of waterborne emissions, generally increases from 1999 to 2006, and affects the sustainability of urban metabolism in Beijing. Results also clearly point out that both direct and indirect inflows should be taken into account, in order to properly assess the economic and environmental consequences of solid waste generation and emissions to air and water. The emergy synthesis method shows to be very appropriate to account for large scale and indirect costs generated by pollution, as side effects of economic activity. Such knowledge is a necessary pre-requisite to perform a reliable cost-benefit evaluation of urban sustainability strategies, and provide guidance to policy decisions.