Assessing carbon sink potentials in the built environment: A study of 40 Chinese cities using a bottom-up high-resolution approach

The built environment is typically considered a source of carbon emissions; however, its potential as a carbon sink has largely been overlooked. This study develops a bottom-up high-resolution approach to estimate carbon sinks in 40 Chinese cities, examining both inter-city and intra-city spatial patterns, disparities, and the contributions of various land use types. The results reveal that total carbon sinks range from 13.25 Mt in Lhasa to 628.12 Mt in Beijing. A general spatial pattern is observed, with higher carbon sink values in central urban areas, which progressively decrease towards the peripheries. The carbon sink-to-emission ratio varies from 0.282 to 0.299, with an average of 0.294, suggesting that the carbon sink in the built environment can offset approximately one-third of its own carbon emissions. In addition, the Gini coefficient indicates significant imbalance in the distribution of carbon sinks within the urban built environment, with Wenzhou (0.797) exhibiting the highest inequality. Analysis of land use further shows that residential areas make the largest contribution, accounting for 42.4 % of total carbon sinks. These findings provide a scientific foundation for optimizing urban carbon storage and inform targeted spatial planning policies, thereby supporting low-carbon and sustainable urban development.