The Impact of Land Use Changes on Carbon Flux in the World’s 100 Largest Cities

Urbanization has become an important player in the global carbon cycle, and land use change is the second largest source of carbon emissions. However, despite great advances in remote sensing and satellite imagery, there is no reliable estimate of the impact of land use change on changes in land carbon stock in global cities. This paper quantified the impact of land use change on land carbon flux in the world’s 100 largest cities by using annual land cover data based on LandSat 8 images and land carbon stock parameters provided by the IPCC (Intergovernmental Panel on Climate Change). It was found that significant urban expansion could be observed in 83 cities, while 29 cities showed a deforestation trend, and croplands in 42 cities have shrunk. Carbon stock reduced by more than 112 million tons in the 100 selected cities from 2013 to 2022 due to land cover change. A total of 39 cities showed significant negative trends in land carbon stock that were mainly caused by urban sprawl and shrinkage in forest or cropland, among which Kolkata, Chongqing, Seoul, Guangzhou, and Hefei showed the greatest decline. Because of the growth of forest and cropland, or reduction in barren land and grassland, 28 cities showed clear positive trends in land carbon stock. In order to increase urban land carbon stock, the urban planning of most cities should focus on the protection of forests or afforestation that replace barren land or grassland and should avoid mindless urban expansion.