Analyzing the spatiotemporal carbon change mechanism: a land-based carbon flow network (CFN) for cities

High carbon emissions played a significant role in global climate change, which made cities with rapid urbanization responsible for local carbon mitigation. In this study, a land-based CFN framework was established by taking 15 land use types as different network nodes. The framework was intended to be a dynamic structure containing the carbon emissions/sequestration tracking, land-based carbon network and utility analysis, and carbon change mechanism identification. By taking Guangzhou city as an empirical study, the carbon metabolism patterns were shown as increasing emission expansion and spatial differentiation. The high-level emission patches extended from the city center to the suburb with 1/2 to 1/3 the original size from 2000 to 2020, which featured as land use transition toward T in the north and to C2 in the south. All the changing carbon processes among land nodes were detected to conduct CFN utility analysis for mechanism investigation. Exploitation was found significantly contributed to the carbon emissions in 2000-2005 and fell over time. In the built-up area, the dominant carbon relationship has changed from exploitation to mutualism with enlarged carbon emissions in 2000-2005, 2005-2010, and 2010-2015, and the exploitation became dominant in 2015-2020 with increasing carbon sequestration. Under the increasing competitive relationship, carbon emissions of the related land nodes decreased more than 90% from 2000 to 2020 with favorable mutual restriction between pairwise nodes. It provided valuable insight for the carbon mitigation options at a city level through local urban planning.