Projection of future direct and indirect impacts of urban expansion on carbon storage: A case study in Hubei, China

Urban expansion encroaches on natural habitat, which seriously affects carbon storage which plays an important role in global climate change. The projection of future effects of urban expansion on carbon storage have been the subject of attention, previous studies explored its direct impacts but ignored indirect effects: cropland loss caused by urban expansion needs to compensation from natural habitat for food security, which also affects carbon storage. China, as a populated country, is at an important stage of cropland conservation policies reform, rapid urbanization, and constructing of eco-civilization. In this case, it’s vital to figure out the change of carbon storage due to the direct and indirect impacts of urban expansion in the future. Taking Hubei as the study area, the aim of this study is to project both direct impacts (DI) and indirect impacts (II) of urban expansion on carbon storage during 2010–2030. Three scenarios are developed by integrating the current situation and policies: the scenarios where urban continues to expand and the cropland conservation policies are implemented with the priority to cropland in quantity (S₁), with the priority to cropland in quantity and quality (S₂), with the priority to cropland in quantity and quality, and ecological protection is also concerned (S₃). Results show that, the total loss of carbon storage caused by urban expansion will be 1.83Tg•C (DI: 0.95Tg•C; II:0.88Tg•C) under the S₁ scenario, will be 2.15Tg•C (DI: 1.46Tg•C; II:0.69Tg•C) under the S₂ scenario, and will be 1.49Tg•C (DI: 0.94Tg•C; II: 0.55Tg•C) under the S₃ scenario. This indicates that ignoring the indirect impacts of urban expansion on carbon storage will lead to the underestimation of real impacts of urban expansion with 48%, 32%, and 63%, respectively. This study highlights the importance of taking the carbon storage loss caused by the indirect impacts of urban expansion into consideration.