Building a Hierarchical Sociohydrological Model for Flood-Induced Migration

In this study, a new hierarchical sociohydrological model was developed to capture the complex interactions between society and hydrological processes in flood risk management in a multilayered approach. Conventional sociohydrological models tend to treat local communities as a single homogeneous group and do not adequately reflect actual socio-economic heterogeneity and dynamics among different social groups. This model divides society into multiple socio-economic groups (e.g., low-income, middle-income, and high-income groups) and explicitly considers population movement among these groups, flood damage experiences, and group-specific characteristics such as memory loss rates and preparedness awareness ratios. Furthermore, the impact of social interactions on flood risk management is modeled by introducing equations that capture population movement between groups inside and outside the region.

The site of application of this study is the city of San Mateo, Philippines. San Mateo is currently facing rapid urbanization and frequent flooding of the Marikina River. Through a questionnaire survey of local residents, this study determines key model parameters such as the flood memory loss rate, the ratio of preparedness/awareness, and the rate of migration between social groups and outside of the region. Based on these parameters, the study simulates the differences in flood damage and adaptive capacity to flood risk among the different groups, and quantitatively assesses the impact of changes in levee heights and flood experiences on each group.

This study provides a new tool to identify the impact of socio-economic heterogeneity in flood risk management and to assist in the design of realistic and equitable adaptation measures. The usage of a hierarchical model emphasizes the importance of risk assessment and policy making that takes into account social diversity, and demonstrates its applicability to the target site.