How has Beijing's urban weight and composition changed with socioeconomic development?

A city's in-use stock comprises the built environment and manufactured products, which shape a city's weight and play vital roles in human activities. However, researchers have not accurately quantified urban weight and its composition, or how stock types change during urbanization. We quantified Beijing's in-use stock from 1978 to 2015 by bottom-up material-flow analysis for building, infrastructure, and manufactured product stocks, with 11 sub-types (e.g., roads), and 54 accounting items (e.g., expressways). We discuss the driving factors for changes in these stocks and their composition. Beijing's in-use stock increased from 224 Mt in 1978 to 1925 Mt in 2015, an increase of nearly 9 times (19 times the global stock per unit area). This resulted primarily from increases in stocks that accounted for >20% of the total: urban residential buildings (30%), non-residential buildings (26%), and roads (20%), which grew to 15, 5, and 11 times the 1978 levels, respectively. However, the growth rate of these stocks slowed by the end of the study period. Manufactured products represented <4% of the stock, but grew fastest (increasing to 41 times the 1978 value), especially for durable consumer goods and vehicles. This category cannot be neglected because of the increasing purchasing power of residents. The trends for the stock weights remained strongly coupled with population factors, whereas the stocks showed relative decoupling from economic factors (e.g., GDP, investment). These results will help policymakers diagnose problems with Beijing's urban development, thereby improving estimates of future resource demand and providing insights into strategies to slow the increase in urban weight.