Abstract

The main objectives of this study are to assess the regional distribution of sea level in terms of trend and interannual varibility and to analyze the impacts of climate variability modes such as El Niño-Southern Oscillation (ENSO) events, Tropical Atlantic Climate Modes of Variability (TACMV), North Atlantic Oscillation (NAO) on interannual variability and trend of sea level near the West Africans coasts. Indices associated with these phenomena are from the National Oceanic and Atmosphere Administration (NOAA), the Global Mean Sea Level (GMSL) time series provided by AVISO (Archiving Validation and Interpretation Satellite Oceanographic Center) and the Regional Mean Sea Level (RMSL) gridded data by CMEMS (Copernicus Marine Environment Monitoring Service). The results show that the mean regional trend of sea level is similar to the global one but the time evolution at interannual and decadal scales does not follow the pattern of global sea level. Our analysis suggests an influence of ENSO events in the Atlantic coast of West Africa. In particular, we observed negative RMSL anomalies during the two strongest El Niño events (1997-1998 and 2015) and a strong positive RMSL anomaly during the La Niña event of 2011 (the strongest over the last two decades). The analysis also reveals an influence of TACMV and NAO on the interannual sea level variability, essentially through regional Sea Surface Temperature (SST) changes. The study shows that a time series of at least 10 years is required to estimate the trend in sea level rise in West Africa. Sub-decadal trends, primarily reflect natural climate modes, rather than variations in climate change. This study also shows that the distribution of sea level rise in the West African region is heterogeneous with higher values near the coast of West Africa and near the equator.

Key words: West Africa, Sea level rising, Regional sea level variability, Climate Variability Modes, sea level interannual variability.