C4 Economic evaluation of NbS using an integrated assessment model

To develop a framework integrating economic and ecosystem models, we combine an economic model, including land use, with a coastal ecosystem model to evaluate the NbS spatial plan for Majuro Island. For the land use model, we collect data on current land use and build an urban economic model based on certain assumptions regarding transportation (commuting, school, and shopping). We then extend the ecosystem portion of the urban economy and ecosystem model developed by Yoshida and Kono (2020, 2022; Table 2) to the coastal area. We also consider sand supply from coral reef foraminifera, which impacts both land maintenance and ecosystem functioning.

The economic model is characterized by incorporating overseas households and governments to represent the MIRAB economy and explicitly considering fisheries. The land use model uses a standard urban economic model. However, since commutes and school destinations are not located at a single point, we expand this area accordingly. The ecological model considers coral reefs, the foraminifera that inhabit them, and fish as marine resources influenced by the coral reefs. If necessary, we plan to address the predator-prey relationship in detail for fish. Regarding the ecological model, we will incorporate as much as possible the important element from Yoshida and Kono (2020, 2022; Table 2): "Plants and animals also move to areas that are favorable for them." The link between the economic model and the ecological model is the land area supply provided by fisheries and fish, and sand supply from foraminifera and coral reefs.