Risk Assessment of the 2022 Nigerian Flood Event Using Remote Sensing Products and Climate Data

Hydrological extremes, particularly floods, are becoming prevalent in parts of Nigeria. During the 2022 rainy season, Nigeria experienced a devastating riverine flood with severe societal impacts. However, the principal factors contributing to riverine flooding in Nigeria remain debatable, necessitating data-driven and policy-relevant studies to quantify the primary causes of riverine floods in Nigeria. In this study, we applied remote sensing techniques and climate data to characterize the 2022 flood event in Nigeria by quantifying the flooded areas, the number of people affected per state, and riverine flood risk assessment. We investigated rainfall and soil moisture anomalies during the flood event and inferred the contribution of the opening of the Lagdo Dam, in Cameroon, to the severity of the flood event. Our results show that large parts of Cameroon and northern Nigeria experienced above-average rainfall during the 2022 rainy season, contributing to soil saturation. About 50,000 ha of land were flooded in Nigeria between July and August; however, following the opening of the Lagdo Dam in September, the flood extent spiked to 200,000 ha (i.e., about 300% increase), suggesting that excess water from the Lagdo Dam, coupled with inadequate drainage infrastructure, amplified the flood extent in Nigeria. Flooded areas were more extensive in northern Nigeria than in southern regions; however, due to denser settlements in flood-prone areas, Anambra State in southeastern Nigeria was the most affected in terms of people impacted. Therefore, besides rainfall changes and inadequate drainage infrastructures leading to the inundation of the major rivers in Nigeria and their tributaries, we also ranked poor town planning against the population density per square meter as a critical factor that amplifies the societal impacts of flooding in Nigeria. Finally, based on the 2022 conditions and the available pre-flood population data, an estimated number of 105,000 people are at critical risk of riverine flooding in Nigeria.