Aymar Yaovi Bossa^{1, 2,}, Abimbola K. Jallal Dine Boko¹, Yira Yacouba³, Jean Hounkpè^{1, 2}

Concerns related to the variability of hydrological extremes (flows) and their consequences require special attention in the management and use of water resources both globally and in Benin. This study evaluates the recent evolution of flows likely to lead to flooding in the Ouémé basin at the outlet of Bonou from indicators of hydrological extremes. The methodological approach focuses on the analysis of time series of flows from 1986 to 2016 based on several indicators and statistical tests of trend and break. The indicators include the annual maximum discharge (Qmax), the annual maximum of the three-day averages (Qmax3), the fifteen days average (Qmax15), of thirty-day average (Qmax30), etc. The Pettitt test application reveals no break in the series of Qmax3, Qmax15, Qmax30, and Qmax at 3 stations (Bétérou, Savè, Bonou). The Mann-Kendall test at the Bétérou and Savè stations does not reveal any significant trend in the series of flows. On the other hand, there is a downward trend in the Qmax, Qmax3, and Qmax7 series at the Bonou station. Indices such as the 95th and 99th percentiles were used respectively to characterize high and very extreme flows that could cause flooding. These indices could be used to monitor extreme flows that may cause socioeconomic and environmental damage. Given the persistence of floods, it is necessary to update the early warning system by taking into account the new indicators identified in this work to prevent and reduce vulnerability to floods.

Indicators, Hydrological extremes, Exceeded flows, Floods, Ouémé basin