From Material Accumulation to Carbon Lock-In: Spatiotemporal Dynamics of Building Material Stocks and Embodied Carbon in the Guangdong–Hong Kong–Macao Region

Existing studies on embodied carbon in buildings have mainly focused on total accounting or single intensity indicators, with limited attention to long-term material accumulation, annual incremental embodied carbon, and inter-city differences in carbon lock-in risk. This study examines the Guangdong–Hong Kong–Macao region, comprising 21 prefecture-level cities in Guangdong Province together with Hong Kong and Macao. Based on 1 km gridded building material stock data from 2010 to 2020, we combined stock-difference and embodied carbon accounting, spatial autocorrelation and hotspot analysis, population- and economy-based intensity assessment, and urban typology identification to reveal the spatiotemporal differences in material accumulation, annual incremental embodied carbon, and carbon lock-in risk. The results show that cumulative building material stocks increased by 19.41% from 2010 to 2020, while annual incremental embodied carbon declined from 100.60 Mt CO2 in 2011 to 24.34 Mt CO2 in 2020, a decrease of 75.81%. This indicates that continued long-term material accumulation coexisted with a substantial decline in current incremental carbon pressure. Spatially, annual incremental embodied carbon contracted from continuous high-value belts to a small number of localized growth nodes, forming a clear “contraction–concentration” pattern. Clear mismatches were also observed among population-based intensity, economy-based intensity, and local hotspots, indicating that lower citywide average intensity does not necessarily imply lower carbon lock-in risk. By further integrating existing stocks, lock-in formation pressure, and efficiency burden, the 23 cities were classified into five combinations of carbon lock-in risk. These findings suggest that regional low-carbon governance of buildings should move beyond a singular focus on new construction and toward lifecycle-based differentiated management that jointly addresses existing stock renewal, remaining incremental pressure, and local hotspots.