Spatio-temporal variability of flooded areas in the Ouémé floodplain (Benin, West Africa) from 2015 to 2023

International audience Study region: Ouémé floodplain, southern Benin, West Africa.Study focus: The Ouémé floodplain is a vast hydrological system feeding the Nokoué lagoon viathe Sô and Ouémé rivers, crossing an extensive wetland region. Driven by the African monsoon,this area is marked by pronounced seasonal and interannual hydrological variability, leading torecurrent flooding that significantly threatens local communities’ safety and livelihoods. Thisstudy aims to assess the spatio-temporal variability of flooded areas in the Ouémé floodplain from2015 to 2023, using both in-situ measurements and satellite remote sensing.New hydrological insights for the region: The analysis reveals a clear seasonal cycle of flooding,modulated by interannual variability. Sentinel-1A data show that flood extent fluctuates widely,ranging from 20 to 160 km², and identify the Sô region as the most flood-prone area. Importantly,the study detects a significant upward trend in flood extent over the study period. Flood dynamicsare primarily governed by cumulative January–September rainfall, with a critical threshold of1070 mm beyond which flooding expands rapidly. Altimetry data further indicate that a 6 m risein water surface elevation north of the Ouémé river results in increased flood expansion. Tem­porary hydrological connections appear during flood events, adding complexity to floodplainhydrodynamics and enhancing connectivity across the basin. Overall, this study provides newinsights into the mechanisms driving floods in the Ouémé floodplain using remote sensing.