Spatially explicit subpixel-based study on the expansion of impervious surfaces and its impacts on soil organic carbon

Precise spatiotemporal datasets of impervious surfaces (IS) are essential for evaluating urbanization processes and associated soil organic carbon (SOC) dynamics. However, spatially explicit studies on SOC stocks based on high-quality IS data remain deficient, which affects the accuracy of urban SOC budgets. In this study, we used 30-m Landsat images and a subpixel-based model to accurately evaluate and quantify the annual IS of Kaifeng, an ancient city in China that experienced intensive urbanization from 2000 to 2020. Soil organic carbon (SOC) dynamics were further estimated and spatially exhibited based on the SOC densities (SOCD) of different land covers observed in the field. Our results demonstrate that Kaifeng experienced drastic IS expansion from 2000 to 2020, both in total area (an increase of similar to 154.35%) and density (56% vs. 72%). Spatially, IS mainly sprawled to the west, and infilling was observed in the old town. Moreover, the expansion of IS in Kaifeng has resulted in a total of 0.08 Tg (1Tg = 10(12) g) of SOC loss over the past 20 years, and the study area has acted as a clear carbon source. The greatest SOC losses occurred during 2010-2015, mainly in the west, with >30% (similar to 0.024 Tg) of the total loss occurring between 2010 and 2015. This study provides new insights into urban growth through the mapping of growth patterns in terms of both outward sprawl and infill. Our research also could provide a scientific basis for urban planning that seeks to control the rate and spatial pattern of IS expansion, and guide urban greening projects to mitigate the loss of SOC and protect the carbon sequestration capacity of urban soil.