Future socioeconomic development along the West African coast forms a larger hazard than sea level rise

Coastal regions globally face increasing vulnerability to sea level rise (SLR), with significant threats to coastal populations and assets. West Africa (WA), with its extensive low-lying coastline and rapidly growing population, is particularly at risk. The economic losses from floods and storms have been increasing in the 21st century, primarily due to socioeconomic changes and altered climate patterns in high-hazard areas. Even a small difference in global SLR projections can result in substantial additional flood costs. The impacts of SLR are disproportionately felt by impoverished populations in developing countries, particularly in Africa, where low adaptive capacity exacerbates the issue. Human activities linked to socioeconomic development in coastal zones, such as urbanization and infrastructure development, further exacerbate relative SLR and coastal flood risks through subsidence. WA, characterized by low-lying areas, rapid population growth, and intense economic development, necessitates understanding future SLR and coastal flooding to inform policy and identify regional hotspots requiring detailed investigation.

Previous research has estimated coastal vulnerabilities and the value of assets exposed to coastal water levels (CWLs) in the absence of coastal defenses along the West African coast. Studies indicate that flood risks are significantly driven by socioeconomic change, with the potential for absolute flood damage to increase substantially by 2100 without mitigation. Climate change and risky urbanization patterns are expected to further worsen flooding risks. The projected growth of megacities along the West African coast, coupled with the concentration of economic activities in coastal zones, necessitates a comprehensive understanding of the interplay between SLR and socioeconomic development in shaping future flood risks.

This study employs a bathtub modeling approach to assess future coastal flooding in WA. The model uses MERIT DEM and gridded population and GDP datasets consistent with Shared Socioeconomic Pathways (SSPs). Coastal water levels (CWLs) are estimated considering tide, wind, storm surge, and sea level anomaly. Future projections are made using four IPCC Sixth Assessment Report SLR scenarios (SSP1-2.6, SSP4-5.4, SSP3-7.0, and SSP5-8.5). The model combines these CWL projections with population and asset data to estimate exposed populations and assets under different scenarios. To estimate exposed assets, the study assumes asset values are directly proportional to population area, applying GDP per capita rates and an asset-to-GDP ratio. The relative contributions of SLR and socioeconomic factors to coastal flood risk are analyzed by comparing impacts under different scenarios.

The study projects a significant increase in coastal water levels (CWLs) in WA by 2100 under all considered SSP scenarios. The exposed population to coastal flooding is projected to increase dramatically, ranging from a 9- to 16-fold increase across scenarios compared to 2015. Similarly, exposed assets are projected to increase by a factor of 100-300. Nigeria, Senegal, Côte d’Ivoire, Benin, and Ghana are identified as countries with the largest coastal populations and assets at risk. While SLR will be the dominant factor in some countries (e.g., Guinea Bissau, Mauritania), socioeconomic development will be the primary driver of increased coastal flooding risk at the regional level. The study highlights the uneven distribution of risk across WA countries, with Nigeria bearing the brunt of the impact, holding more than 50% of the coastal population at risk in 2100 under SSP5-8.5.

The findings underscore the significant role of socioeconomic development in shaping future coastal flood risks in WA, exceeding the contribution of SLR in many regions. This highlights the need for integrated coastal zone management strategies that account for both climate change impacts and rapid socioeconomic development. The concentration of risk in specific countries, particularly Nigeria, necessitates targeted interventions to protect vulnerable populations and assets. The study's results reinforce the call for sustainable coastal development practices that balance economic growth with environmental protection and risk reduction.

This research emphasizes the critical need to incorporate socioeconomic development dynamics into coastal flood risk assessments. While sea level rise poses a significant threat, socioeconomic factors drive the greatest increase in future coastal flood risk in West Africa. Sustainable coastal planning that balances development with environmental protection and risk mitigation strategies is essential to safeguard the region's vulnerable coastal communities and assets. Future research should focus on high-resolution data collection to refine model accuracy and address uncertainties, particularly regarding land subsidence. Further investigation into community-based adaptation strategies is needed to ensure effective risk reduction.

The study acknowledges inherent uncertainties in its methodology, particularly those related to elevation data and socioeconomic development projections. The use of a bathtub model, while useful for regional-scale assessment, may not capture the complexities of local hydrodynamic processes. The assumption of direct proportionality between asset values and population density simplifies a complex reality. Data limitations on high-resolution elevation data, especially in Africa, hinder the accuracy of the model's projections. These limitations suggest that the findings represent a first-order evaluation of future coastal flooding risks.