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In West Africa, as in many other estuaries, enormous volumes of marine water are entering the continent. Fresh water discharge is very low, and it is commonly strongly linked to rainfall level. Some of these estuaries are inverse estuaries. During the Great Sahelian Drought (1968–1993), their hyperhaline feature was exacerbated. This paper aims to describe the evolution of the two main West African inverse estuaries, those of the Saloum River and the Casamance River, since the end of the drought. Water salinity measurements were carried out over three to five years according to the sites in order to document this evolution and to compare data with the historical ones collected during the long dry period at the end of 20th century. The results show that in both estuaries, the mean water salinity values have markedly decreased since the end of the drought. However, the Saloum estuary remains a totally inverse estuary, while for the Casamance River, the estuarine turbidity maximum (ETM) is the location of the salinity maximum, and it moves according to the seasons from a location 1–10 km downwards from the upstream estuary entry, during the dry season, to a location 40–70 km downwards from this point, during the rainy season. These observations fit with the functioning of the mangrove, the West African mangrove being among the few in the world that are markedly increasing since the beginning of the 1990s and the end of the dry period, as mangrove growth is favored by the relative salinity reduction. Finally, one of the inverse estuary behavior factors is the low fresh water incoming from the continent. The small area of the Casamance and Saloum basins (20,150 and 26,500 km² respectively) is to be compared with the basins of their two main neighbor basins, the Gambia River and the Senegal River, which provide significant fresh water discharge to their estuary.

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En Basse-Casamance, la mangrove constitue un écosystème particulier qui abrite de nombreuses ressources et reste le siège des principales activités rurales. Dans la zone d’Oussouye, cette mangrove a connu une régression importante au cours des décennies 1970 et 1980. L’étude de sa dynamique spatio-temporelle, à partir des outils de la géomatique couplés à des enquêtes de terrain, a permis d’appréhender son déclin, entre 1972 et 1994 de -42 % ; et son évolution positive de +22,44 % entre 1994-2018. Les facteurs à l’origine de la régression durant les années 70 et 80 sont principalement le déficit pluviométrique avec comme conséquences la salinisation et l’acidification des terres, et la faiblesse de la régénération naturelle. L’étude a aussi montré que les actions anthropiques telles que la coupe du bois pour diverses raisons et des racines échasses ont longtemps porté préjudice aux écosystèmes de mangrove. La reprise constatée au cours des dernières décennies est à replacer dans le contexte du retour de la pluviométrie à une situation meilleure et à la prise de conscience des populations du rôle stratégique et important de la mangrove.

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