Understanding the drivers of Extreme Coastal Water Levels in West Africa from oceanic and climatic processes

Abstract Rising sea levels pose a major threat to West Africa's densely populated and economically important coastal regions, which extend from Mauritania to Cameroon. Here, we explore the dynamics of Extreme Coastal Water Levels (ECWLs) from 1994 to 2015, with the aim of enhancing disaster management and prediction strategies. We found that regional differences in ECWL are primarily driven by tidal forces and wave runup, which have a direct impact on coastal erosion and floods, particularly in areas like Guinea-Bissau. This area is highly susceptible due to its wide low-lying coastal plains, which exacerbate the effects. Sea Level Anomalies (SLA) also play a critical role, as they reflect the cumulative effect of oceanographic and climatic conditions, exacerbating the impacts of tidal and wave dynamics. Although less significant, atmospheric contributions influence ECWL through storm surge and wind pattern variations. Regional climatic phenomena, particularly the Atlantic Niño, significantly influence the West African Monsoon, altering rainfall patterns and ECWL. In contrast, global climatic drivers such as the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) have a more subdued influence due to their less direct impact on local atmospheric conditions. Using a strategic cluster study based on annual tide and wave data, we categorise West African countries into distinct groups, enabling tailored and effective flood mitigation strategies that are aligned with their specific hydrodynamic and climatic characteristics. The study highlights the importance of tailored climate models and monitoring systems that focus on regional climate indicators such as the Atlantic Niño, which are essential for accurately predicting and managing the effects of climate changes on coastal areas in less developed countries.