Predicting future coastal land use/cover change combining CA-Markov and Sea Level Affecting Marsh Models in the Northwestern Coastline of Guinea-Bissau

Modeling coastal land use/cover (LULC) change is one of the most accurate methods for understanding historical LULC change. In this study, we first time combined Land Change Modeler (LCM), CA-Markov Model and Sea Level Affecting Marshes Model; then merged the local study area’s sea-level rise (SLR) data with future representative concentration pathway (RCP8.5) scenario, and modeled the coastal LULC changes over the past two decades, predict future coastal LULC change and, project future impact of SLR on the coastal LULC in the short-, medium- and long-term in the Northwestern Coastline of Guinea-Bissau (NC-GB). The study revealed that, the study area experienced considerable coastal LULC change between 2000-2020. The study observed the gains in two coastal LULCs, including tidal flats, whose change was driven mainly by sea level with a total net gain of 57.93 km², and mixed forest with a net gain of 25.90 km². We also observed the significant loss of developed land whose change was influenced by mixed forest and tidal flat with a total loss of -75.58 km². The low coastal elevation of less than 1m below the mean sea level and flat slope of less than 2 degrees were identified as the primary drivers of coastal LULC change in the NC-GB. The study concluded that from 2020 to 2060, the tidal flat will observe a remarkable net gain of 80.55 km²; these gains will make developed land the most impacted land use in the next six decades with 63%, followed by mangrove with 23%, and mixed forest 12%, respectively. This unprecedented impact of developed lands will inevitably threaten the study area's socio-economic development and food security. These findings can support coastal planners and policy-decision makers to take timely actions by enabling sustainable mitigation and development programs to prevent the future impacts.