Urban weight and its driving forces: A case study of Beijing.

Massive resource and energy consumption greatly increase a city's domestic material consumption (its "weight"), resulting in proportionally large pressure on the environment. Understanding the causes and driving forces behind urban weight can therefore promote more sustainable urban development. To improve our understanding, we analyzed the composition of Beijing's urban weight from 2000 to 2015. We then defined the key metabolic processes (including both metabolic components and paths between them) that contributed to weight changes during this period using the logarithmic mean Divisia index model to identify the underlying driving forces. Beijing's weight grew by 82.6% during the study period, with non-metallic minerals being the material most consumed (about 45% of the total weight). Beijing depended heavily on imports, and extraction within the city's administrative boundaries has gradually declined. The Construction and Industry sectors were the dominant metabolic components; their material exchanges with both the internal and external environments of the city represented the largest flow pathways. The largest proportion of urban weight that was dissipated was air pollution, which therefore represents the biggest environmental challenge facing Beijing. Economic activity was the largest driver of urban weight growth, followed by population growth, with decreasing material consumption intensity (per unit GDP) somewhat reducing the city's weight. The results help us to understand the characteristics of urban weight change over a long period, and this knowledge can be used to prioritize structural adjustment, determine targets for regulation, refine processes, and guide future policy development to focus on the drivers of weight change.