Physical Forcing Induced Coastal Vulnerability along the Gulf of Guinea

Coastal areas of the Gulf of Guinea experience accelerated degradation as a result of erosion and flooding associated with intensification of extreme marine-meteorological phenomena. The coastal erosion process, especially on the sandy or muddy littoral, constitutes one of the main factors of the degradation of the Gulf of the Guinean coast. These risks, which are still poorly studied, could increase over the coming decades because of climate change and the human activities that exacerbate them. Data related to ocean forcing (tide, wave, and sea level anomaly), to hydrologic parameter (rainfall) and to the state (geomorphology, coastal slope, and rate of coastal retreat) of the coast were analyzed by several statistical methods and a numerical vulnerability model to map the vulnerability of the different coastlines of this region. The results showed that the vulnerability of these coastal areas is influenced by geomorphology, tide, waves and rainfall intensity. 24.34% and 37% of the entire coast are of low and moderate vulnerability respectively. While 26.98% and 11.66% are of high and very high vulnerability respectively. This information could facilitate developing sustainable policies to effectively manage hazards in this coastal zone.

Seasonal Variability of the Buoyancy Flux along the Northern Coast of the Gulf of Guinea

The buoyancy flux Bo at the air/sea interface is very useful to understand the variability of the stratification of the mixed layer, the oceanic mixing, the phytoplankton dynamics and then the coastal upwelling. The atmospheric reanalysis ERA5 and the oceanic reanalysis ORAP5 data have been used in this study to describe the sea surface Bo and, its influence on the variability of the mixing in the mixed layer and consequently on the coastal upwelling along the northern coast of the Gulf of Guinea. The Bo is negative along the coast and, is characterized by a seasonal variability dominated by the thermal buoyancy flux. This study has also shown that the mixing layer is very shallow along the coast and deeper offshore. The negative value of the Bo increases the stratification of the mixed layer and reduces the mixing. This could explain why the mixed layer is shallow in this region. This work suggests that an increasing trend of the global warming could have dramatic impact in this area by increasing the stratification in the mixed layer and would contribute to reducing the coastal upwelling intensity.

Development of an Integrated Coastal Vulnerability Index for the Ivorian Coast in West Africa

This study assesses the vulnerable state of the 566-km Ivorian coastal area using the physical (geomorphology, coastal slope, coastal retreat rate, relative sea level rise and wave/Tide energy) and socio-economic (coastal population density, harbor, airport, road, land use and protected area) factors as indicators. This enabled an Integrated Coastal Vulnerability Index to be determined for the Ivorian coastal zone. This Index could be defined as the weighted average of indexes based on physical and socio-economic factors. The study revealed that vulnerability of the western and the eastern coastlines of Cote d’Ivoire are strongly influenced by human activities, while physical forcing affects significantly the vulnerability of the central section. The relative vulnerability of the different sections depends also strongly on the geomorphology, wave energy, coastal population density and land use factors. The west and central sections of the coastline are more resilient than the eastern section when integrating physical and socio-economic factors. The Integrated Coastal Vulnerability Index, based on physical and socio-economic factors, appears to be more appropriate for coastal vulnerability assessment. These results could be useful in the development of adaptation strategies to increase the resilience of this coastal area and then extended for West Africa Coastal Areas Management.