Compound-event analysis in non-stationary hydrological hazards: a case study of the Niger River in Niamey

This study examines compound hydrological hazards in a non-stationary context, specifically focusing on the Niger River in Niamey. The hazard results from the confluence of local Sahelian and more remote Guinean tributaries, displaying seasonal floods. The study first investigates whether Niamey’s annual flood hazard is a compound result of Sahelian and Guinean flows, and then assesses the value of a compound hazard approach versus traditional flood analyses in this region. Analyzing discharge data from 1950 to 2020, the study disentangles Sahelian and Guinean flow impacts. It compares flood return level estimations from three statistical models of varying complexity. Findings confirm Niamey’s hazard as compound, stressing the need to consider both tributaries separately. Incorporating non-stationarity in statistical modeling is crucial, yet fully integrating the compound nature of hazards doesn’t significantly change the quantitative estimation of the hazard in Niamey.