A revisit of Niger river’s major flood events and the role of convective systems with satellite data and hydrological modeling

The study focuses on the Niger river in West Africa. The impact of tropical convection on extreme phenomena like the recurrent floods of the Niger river in Niamey is analyzed. A new method based on meteorological satellite data and hydrological modeling is used to analyze the intersection between the trajectory of the storms and the hydrological basin. The total volume of rain brought by each mesoscale convective system (MCS) crossing the water shed is quantified. The method is applied to decompose the hydrograph of the Niger river in Niamey and highlight the impact of the major rain events on the record flood of 2020. The role of the MCSs crossing the subbasins contributing to the phenomena of the red flood in Niamey is highlighted. The 10 MCS that brought the largest volumes of rain over the area explain about 50 % of the discharge peak that lead to serious flooding in 2020. The rainiest MCS caused a rise of about 17 % with a lasting effect over more than a week. These figures illustrate that detecting major MCSs and quantifying the associated rain volume could help in flood prediction in a region very impacted by these phenomena. ● The impact of individual storms on the discharge of the Niger river in Niamey during extreme red floods is quantified using storm tracking, satellite based rainfall estimates and a hydrological model. ● A single rain event explains up to 17 % of the discharge maximum in Niamey during the record flood of 2020. ● The 10 rainiest storms out of a total of more than 100 MCS in 2020, explain 50 % of the discharge during the flood peak. ● Monitoring MCS’s trajectories and intensity could help improve flood risk warning with a lead time of about 7 days.