Tracking urban metabolism flows through the lifecycle of buildings, infrastructure, and durable goods at material, product, and sector levels

Abstract

The functional roles and environmental effects of long-lived buildings, infrastructure, and durable goods can determine both the benefits to natural environment and a city's human residents. However, their overall lifecycle metabolic processes are complicated and previous studies mainly considered specific materials or products. Here, we provide a more comprehensive picture of flows and stocks for Beijing's materials, products (61), and sectors (9). Based on a multi-level material stock–flow network model, we obtained insights into the city's material inputs and outputs of each urban sector, the cumulative flows of materials and products, and the waste sources for end-of-life products. From 2000 to 2018, the total system throughflow increased from 269 to 435 Mt by 2007, then decreased to 317 Mt. Beijing's main sector of consumed resources and discharged wastes both shifted from Fabrication and Manufacturing to Construction. The local extraction and production weights decreased by half, whereas the inflows to the Construction and Transportation sectors increased greatly, mainly (92%) as imports (from regions other than Beijing). The main destinations of these materials were buildings and pipelines, which were also main waste sources. Notably, resource demand and waste discharge from vehicles and railways increased greatly. Although Beijing's recycling increased, it must increase further to meet final waste generation, which has increased 5-fold, to 52 Mt in 2018 during the city's socioeconomic development. Additional actions should be taken to reduce waste streams and promote reuse and recycling to achieve the UN Sustainable Development Goals.