Impact of shoreline changes on population in Cotonou, Benin

The coast of Cotonou (Benin) is affected by an intensive coastal erosion for several decades, mainly due to unsuitable port infrastructures and human activities. In the future, the process will very likely be worsen by sea level rise as a consequence of global warming. In this study, we use a combination of very high resolution satellite images from Google Earth recorded in 2002, 2011, 2013 and 2014 and carry out field missions in September 2012, September 2013, July 2014 and February 2015 to assess the retreat of the coastline and to understand the dynamic of population in the risk area. Multi-temporal analyses of satellite images show that nearly 93 hectares of land (including 40 hectares off) were progressively eroded by the sea between 2002 and 2014 on the stretch of the first eight kilometers at the east of the Safiato groyne. This corresponds to an average coastline’s retreat of 115 meters in 13 years, with variations from 38 to 145 meters, depending on the location. Thanks to the comparison between the images of 2002 and 2014, we assess that around 765 houses disappeared by the encroachment of the sea over the distance of 8 km to the East of the Safiato groyne, of which 60 villas and about 705 makeshift houses (informal settlements). Well-off population leave the risk area when their houses are threatened and go inland, fishermen prefer to stay in the risk area to be close to their activities and precarious population have no financial and social capitals to migrate, they are trapped in the risk area. Other precarious population coming from somewhere else settle in the coastal area and grow the at-risk population. The use of intermediate images and the results of field works confirm a rapid process of settlement/destruction of makeshift houses in the coastal area. Poor people carry out simply short displacements in the risk area. There is an urgent need to secure these populations. Update and respect of urban planning regulations, good governance, cooperation with other countries and involvement of local communities are all factors that are expected to reach this objective.