Analysis of extreme rainfall in Oti River Basin (West Africa)

Understanding how extreme rainfall is changing locally is a useful step in the implementation of efficient adaptation strategies to negative impacts of climate change. This study aims to analyze extreme rainfall over the middle Oti River Basin. Ten moderate extreme precipitation indices as well as heavy rainfall of higher return periods (25, 50, 75, and 100 years) were calculated using observed daily data from 1921 to 2018. In addition, Mann–Kendall and Sen's slope tests were used for trend analysis. The results showed decreasing trends in most of the heavy rainfall indices while the dry spell index exhibited a rising trend in a large portion of the study area. The occurrence of heavy rainfall of higher return periods has slightly decreased in a large part of the study area. Also, 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. The novelty of this study lies in the combination of both descriptive indices and extreme value theory in the analysis of extreme rainfall in a data-scarce river basin. The results are useful for water resources management in this area. HIGHLIGHTS Observed trends of extreme rainfall in the Oti River Basin from 1921 to 2018.; The occurrence of heavy rainfall of higher return periods has slightly decreased in a major part of the study area.; Consecutive dry days index has increased in a large part of the study area.; Generalized Extreme Value is the best three parameter distribution for analyzing the frequency of extreme rainfall in the Oti River Basin.