Urban metabolic performance and spatiotemporal evolution in central Beijing: a community-scale emergy accounting study

Introduction Urban areas are central to resource consumption and carbon emissions, yet community-scale metabolic mechanisms remain underexplored, particularly when green-space ecosystem services are incorporated into emergy accounting. Methods Taking the 305.8 km 2 central area of Beijing as a case and communities as analytical units, this study develops a community-scale emergy accounting framework for 2011, 2014, 2017, and 2020. Green-space carbon sequestration and oxygen release are included as explicit output emergy. Results Emergy per area (EPA) was high and spatially uneven. Emergy per capita (EPP) was higher in 2020 than in 2011 in most communities, and its spatial disparities narrowed. The emergy yield ratio (EYR) remained below 1. The environmental loading ratio (ELR) rose from mostly 3-10 in 2011 to above 10 in many communities by 2020, and the environmental sustainability index (ESI) remained below 1. Within this accounting framework, expanding green space within community boundaries can only marginally improve the direct accounted output emergy and cannot raise ESI above 1; the limiting factor is the renewable fraction of external supporting flows. With only four observation years, these temporal changes cannot be attributed to specific policies as opposed to interannual fluctuations. Discussion Differentiated community governance should prioritize energy-efficiency retrofits and circular economy pilots in low-EYR areas, functional green infrastructure in high-ELR areas, and, more fundamentally, an increase in the renewable fraction of external supporting flows. The study advances community-scale urban metabolism accounting for SDG 11 while highlighting boundary, data, and methodological limitations.