Modeling urbanization impact on surface runoff in a West African city: A case study of Dakar’s suburbs (Senegal)

Abstract

Urbanization profoundly modifies hydrological processes by altering natural drainage pathways, reducing infiltration, and increasing surface runoff volumes.In rapidly expanding cities such as Dakar, these changes are exacerbated by unplanned development and limited stormwater infrastructure.This study aims to assess the hydrological impacts of urbanization by implementing a rainfall-runoff model adapted to data-scarce environments.The model was calibrated using the limited hydrological and meteorological observations available, along with integrated spatial indicators representing both urbanization density and the modification of natural drainage directions.Simulations were carried out for identical rainfall events under two contrasting land-use scenarios, corresponding to the years 1983 and 2018.The results reveal a marked increase in runoff levels and discharges at the watershed outlets, with amplification factors of 1.75 for watershed 1 and 2.75 for watershed 2. These r esults clearly demonstrate the intensification of surface runoff resulting from increased imperviousness and the densification of the urban fabric.Beyond the quantitative findings, this study highlights the strong relationship between urban growth, flood risk, and urban planning in African cities, where land pressure and informal development are particularly pronounced.The acquisition of additional rainfall-runoff measurements would help refine model calibration, reduce uncertainties, and strengthen the robustness and relevance of the proposed approach.