Increasingly, it is reported that the coastline of the Dakar region is affected by coastal flooding due to extreme water levels during wave events. Here, we quantify the extreme coastal water levels as well as the different factors contributing to coastal flooding during the period 1994–2015. Severe water levels reach values of 1.78 m and increase by 8.4 mm/year. The time spent above this threshold has already increased by 1.7 over the study period and will increase by 2100 to 8 times with 0.4 m mean sea level rise and up to 20 times with 0.8 m in the IPCC low and high greenhouse gas emission scenarios, respectively. Tide is the main contributor to the extremes when combined with large wave runup, due to wave breaking which contributes to 38% of the increase in extreme events while sea level rises to 44%. Our results show that because of its prominent location, Dakar region is affected by waves coming from the Northern and Southern Hemispheres with contrasted evolutions: wave runup events increase faster (7 mm/year) during austral winter due to a maximum of the South Atlantic storm activity, and have a decreasing trend (−3 mm/year) during boreal winter (December, January, February) driven by the evolution of corresponding climate modes.

L’érosion côtière est une des causes de la disparition des plages, du recul des falaises et de la perte de terrains à valeur socio-économique et écologique. La compréhension de la dynamique côtière est donc primordiale avant d’entreprendre toute politique d’aménagement du littoral. Cette étude se propose de retracer la dynamique historique du trait de côte de la zone de Malibu à Malika au Nord de Dakar qui subit actuellement une forte pression humaine avec l’extension de la Voie de Dégagement Nord. Elle est basée sur l’analyse de données de télédétection au moyen du logiciel ArcGIS 10.4 et de l’extension DSAS 4.3 (Digital Shoreline Analysis System). Les résultats obtenus laissent apparaitre, entre 1942 et 2011, une évolution du trait de côte en faveur d’une érosion avec une vitesse moyenne de -0,15 m/an. Cette évolution, qui n’est pas uniforme d’un secteur à un autre mais aussi d’une période à une autre, serait essentiellement due à l’action des agents hydrodynamiques qui gouvernent les mouvements sédimentaires. Néanmoins, la pression humaine commence à se faire sentir avec l’extension de la Voie de Dégagement Nord, les extractions de sables et la coupe des filaos au profit des constructions humaines dont les conséquences sur la dynamique côtière peuvent être alarmantes. Coastal erosion is one of the causes of the disappearance of beaches, retreat of cliffs and loss of land with socio-economic and ecological value. Understanding coastal dynamics is therefore essential before undertaking any coastal development policy. This study aims to retrace the historical dynamics of the coastline from the Malibu to Malika area located in the north of Dakar which is currently under strong human pressure with the extension of the Northern Clearance Way. It is based on the analysis of remote sensing data using ArcGis 10.4 and the DSAS 4.3 extension (Digital Shoreline Analysis System). The results obtained show, between 1942 and 2011, an evolution of the coastline in favor of erosion with an average speed of -0.15 m/year. This evolution, which is not uniform from a sector to another, but also from one period to another, is essentially due to the hydrodynamic agents which govern sediment movements. However, human pressure is starting to be felt with the extension of the Northern Clearance Way, sand extraction and the cutting of casuarinas for human constructions benefit. The consequences of such practices on coastal dynamics can be alarming.