Multi-scenario simulation of land use/cover change and carbon storage assessment in Hainan coastal zone from perspective of free trade port construction

Accurate prediction of future Land Use/Cover Change (LULCC) and its impact on ecosystem carbon storage is of great scientific significance for regional land use decision making and carbon management. However, there are few previous studies that combine spatial and temporal scales to explore the impact of future land use changes on ecosystem carbon storage in coastal zones at the provincial scale. Taking the coastal zone of Hainan Island as an example, Landsat TM (OLI) data from 1990, 2000, 2010 and 2020 were used as the main data sources to analyze the spatial and temporal evolution of land use from 1990 to 2020. The GeoSOS-FLUS model was used to predict land use patterns under baseline, development priority and ecological priority scenarios in 2030. Based on land use data, ArcGIS and Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) models were used to evaluate the carbon storage of ecosystems from 1990 to 2030, to explore the spatial and temporal evolution of LULCC and response of the LULCC to carbon storage, and to reveal the process and mechanism of the impact of the complex land use change process on the carbon sink service function of regional ecosystems in tropical and subtropical coastal zones. The results showed that: 1) From 1990 to 2020, the area of cropland, forest land, grassland and unused land decreased, while the area of water and built-up land increased. Unused land and cropland area continues to decrease, built-up land continues to increase. 2) LULCC has led to a continuous decrease in regional carbon storage over 30 years, reaching 1.5 × 106 t, with an annual change rate of 5.0 × 104 t/a. The extensive expansion of built-up land and the degradation of forest land are significant reasons for the decrease in carbon density, and “unused land→grassland” is the most obvious reason in the carbon storage increase. “Grassland→forest land (artificial)" is the most significant mapping reason in the decrease of carbon storage. The spatial and temporal characteristics of regional carbon storage showed a significant positive correlation with the region, and the wetland and mangrove areas in the southwest and northeast directions were the high-high concentration areas of carbon storage. 3) The built-up land in 2020–2030 shows different degrees of expansion in the baseline, development priority and ecological priority scenarios, with an increase of 1.94%, 2.13% and 0.70% respectively, and the development priority scenario has the largest increase. The cropland showed a shrinking trend in 3 simulated scenarios, and the area decreased by 0.87%, 0.97% and 0.87%, respectively. 4) The regional carbon storage in 2020–2030 decreases significantly under the baseline and development priority scenarios, at 1.29 × 105 t and 2.45 × 105 t respectively, while it increases significantly under the ecological priority scenario, at 1.34 × 105 t. The ecological priority scenario can effectively enhance the carbon sink capacity and control the reduction of cropland area. Optimizing the land use structure, controlling the growth rate of built-up land and increasing the area of forest land can have a positive effect on the development and use of coastal zone space and the carbon cycle.