Effects of land use and transportation on carbon sources and carbon sinks: A case study in Shenzhen, China

Carbon-sink and carbon-source estimation are of significance for carbon-emissions reduction. In this paper, we evaluated Shenzhen's annual carbon budget from 2000 to 2008 by measuring the presence of carbon sinks and carbon sources in the city. First, we used a coefficient approach based on factors such as land-use status and crop yield, to determine the number of carbon sinks in Shenzhen. Second, we identified urban carbon sources such as human respiration, industrial fossil-fuel consumption, cropland soil, livestock and transportation. We used a traffic-prediction tool, namely the four-step model, to determine traffic flow and the average speed of vehicles based on land-use types and the spatial distribution of road networks. Finally, we used the aforementioned methods to estimate the number of carbon sinks and carbon sources in Shenzhen from 2000 to 2008, along with its net carbon source. The results show that the number of carbon sinks decreased and the number of carbon sources increased in Shenzhen between 2000 and 2008. However, the net carbon source per million GDP decreased, which suggests that carbon-reduction efficiency improved during this period. Urban expansion and forest reduction were the major causes of the observed carbon-sink reduction. We identified transportation and industrial fossil-fuel consumption as Shenzhen's main carbon sources. The former produces high concentrations of CO2; the latter is related to the growth of secondary industries. In addition, the spatial distribution of the net carbon source from 2000 to 2008 indicated that Shenzhen's net carbon source increased both spatially and temporally during this period.