Scaling of urban residential building stock system and carbon emissions accounting for vacant houses in China

Urban housing vacancy is an important and sensitive research topic, especially for the development of China. However, the complex relationship between the growth mechanism of residential building stock and housing vacancy remains unclear. An integrated system dynamics model and scaling theory were used to establish an updated understanding of the urban residential building stock growth, and then to explore carbon emissions from vacant houses. We identified universal scaling laws for urban population and residential building stock in a single city, and the building stock growth scaled superlinearly in most cities, with the scaling exponent ranging from 1.00 to 2.50; This growth pattern may exacerbate housing vacancy. It is worth noting that, spatially, the scaling exponents in shrinking urban areas were significantly higher, such as in Harbin (6.16) and Changchun (5.14). Temporally, the scaling exponents decreased with time in most sample cities. Additionally, the per capita carbon emissions during the material production stage of the urban vacant residential buildings of some cities (e.g., Shenyang, Harbin, Changchun, and Sining) with relatively large scaling exponents exceeded 3.00 tCO₂/cap, and the revitalization of vacant houses is extremely important. Thus, city-specific policies based on the scaling exponents and carbon emission intensity associated with urban vacant buildings are important to rationally tap idle building stock and optimize the building supply.