Lianbao Cao

This paper aims to establish a more standardized and regulated carbon emission accounting model for sponge cities by unifying the accounting content for carbon emissions and clarifying the relationships between carbon reduction benefits, carbon reduction effects, and carbon sequestration, in order to evaluate the carbon reduction outcomes and mechanisms of sponge city construction. Based on a Life Cycle Assessment (LCA) carbon emission accounting model using the carbon emission factor method, a newly constructed residential area in Tianshui City, Gansu Province, was selected as a case study, and the carbon emission reduction effect of sponge city construction was then investigated. Results indicated that the 30-year full life cycle carbon emissions for sponge city construction in the newly constructed residential area amounted to 828.98 tons, compared to 744.28 tons of CO₂ reduction in traditional construction, representing a 47.31% reduction in carbon emissions. Over a 30-year life cycle, this equated to a total carbon emission reduction effect of 1460.31 tons. Additionally, under various rainfall scenarios in a typical year, the carbon emission reduction effect of sponge city construction exceeded the carbon emissions, achieving carbon neutrality within 22 to 30 years of operation. This demonstrates that the carbon emission reduction effect of sponge city communities is significant. The findings of this study provide data and a theoretical basis for the low-carbon construction of sponge cities in China.

To investigate the quantitative relationship between the volume capture of rainfall and carbon emissions from bioretention facilities, this study introduces the concept of the carbon intensity of volume capture of rainfall. The influence of four key factors—climatic conditions, aquifer height, permeability coefficient, and facility area—was investigated using a residential neighborhood in Tianshui, China, as an example. The results reveal that the carbon intensity value is influenced not only by external environmental changes but also by the inherent attributes of bioretention facilities, such as aquifer height, permeability coefficient, and facility area. The maximum carbon intensity value for the volume capture of rainfall was −0.0005 kg CO₂/m³, while the minimum was −0.0852 kg CO₂/m³, representing a substantial difference of approximately 169 times. Orthogonal experiments identified the facility area as the most significant influencing factor on carbon intensity, with a correlation coefficient of 0.0520. The area of bioretention facilities can be prioritized to meet deployment requirements, taking into account volume capture reduction effects and carbon emissions. For facilities with a high carbon intensity, an emphasis should be placed on enhancing carbon reduction benefits, and various initiatives can be implemented to achieve this goal.