Post-flood evaluation of the 2010 and 2020 niger river floods in the districts of karimama and malanville in north - benin using remote sensing

Abstract

Due to the recurrence of floods in recent years through the Niger River watershed in Benin, it’s necessary to assess the damage caused in order to consider preventive measures. The main goal of this paper is to evaluate and compare floods impact from 2010 and 2020, which are years of major floods in the Niger basin in Benin, particularly in the districts of Karimama and Malanville. The data used in this study are daily flows and were collected through Malanville hygrometric station (from 1981 to 2020), Gaya synoptic station (from 1981 to 2020) and the sentinel images (September 2010 and September 2020) which are used to calculate satellite indices and produce land use maps. Rainfall and streamflow data, that are factors in the occurrence of floods were analyzed using the reduced centered anomaly method.The satellite data were used to calculate the NDPI (Normalised Difference Pond Index), NDWI (Normalised Difference Water Index) and land cover maps for the same dates. The NDPI is used to delineate dry and water surfaces with greater discrimination, and the NDWI is intended to extract water masses, as it maximizes the reflectance of water in the green wavelengths. The results show that precipitation increased significantly in both years, especially during the months of July, August and September, but the increase in flow was more significant, with more pronounced values in 2020. The floods of 2020 affected 20276.53 ha of fields and 2987 ha of settlements against 17812.28 ha and 2012.17 ha in 2010. Monitoring the level of flood variation by remote sensing would increase the capacity of action of the early warning and risk management system and disasters associated with floods increasingly recurrent in the context of climate change.

Keywords: North-Benin; Niger Basin; floods; remote sensing.