Observed Trends in Heavy Rainfall Over Tropical Catchments: Case Study of the Oti River Basin, West Africa

Climate change has exacerbated heavy rainfall which causes severe floods in West Africa. Global warming accelerates the evapotranspiration process which further alters the rainfall regime due to the increased capacity of the atmosphere to hold moisture according to the Clausius-Clapeyron relationship. Understanding how heavy rainfall events are changing locally is a useful step in the implementation of efficient strategies for flood risk management. This study aims at analyzing heavy rainfall over the Oti River basin. Daily rainfall and temperature data were collected from national meteorological stations in Benin, Ghana and Togo. Thus, seven (07) heavy rainfall indices were calculated using observed daily data from 1921 -2018. The methodology used to estimate heavy rainfall quantiles is an index storm regional frequency analysis based on L-moments of AMAX. The Mann–Kendall and Sen’s slope tests were used for the trend analysis. The results showed decreasing trends in most of the heavy rainfall indices. In addition, the occurrence of heavy rainfall of higher return periods has slightly decreased in a large part of the study area. Also, the analysis of the annual maximum rainfall revealed that the Generalized Extreme Value is the most appropriate three-parameter frequency distribution for predicting extreme rainfall in the Oti River Basin. These results are useful for efficient flood risk management and accurate estimation of design rainfalls in the study area.