Assessment of Flood Risk in Cotonou Areas Surrounding Nokoué Lake Due to the Effect of Climate Change

Abstract

Cotonou, like West African cities, experiences recurrent flooding. This work aimed to study the effect of climate change on the risk of flooding in Cotonou’s zoos on the periphery Nokoué Lake. We analysed climate data (rainfall and temperature) in Cotonou over the period 1953 to 2013, the flow of the Ouémé River at Bonou, and the variation in the height (elevation) of Lake Nokoué. The results of the analysis of temperatures over the period 1953-2013 show an upward break from 1987 onwards (+0.7˚C between 1987 and 2013), while for rainfall, no break was observed over the same period. None of the 13 rainfall indices calculated is statistically significant, but they show a relatively stable or declining trend except for the average daily rainfall, the maximum number of consecutive dry days and the 95th percentile, which all show a slightly upward trend. We have shown that the rainfall recorded in Cotonou does not reveal any abnormal or exceptional character over the last ten years, on the one hand, and the flooding of Ouémé River influences that of Nokoué Lake, on the other hand. This study shows that the floods observed in this area are more related to the effect of climate change.