Contribution of Agro-Hydrological Modeling in the Evaluation of Water Availability of an Ungauged Basin Reservoir in Côte d’Ivoire: Case of the Loka Reservoir in Bouaké

The city of Bouake, the second biggest city of Cote d’Ivoire, experienced a water shortage in 2018 that lasted four months due to the drying up of the Loka reservoir, which supplies two-thirds of the city. The challenge of the Loka reservoir is that it is located in an ungauged basin where very few hydrological studies have been carried out, despite the recurrent problems of access to drinking water. In the purpose to better understand the phenomena that caused this temporary drying of the dam, the methodology implemented was based on agro-hydrological modeling with SWAT using a regionalization technique of a nearby watershed. The model performance was assessed using three statistical indices (the Nash-Sutcliffe coefficient (NS), the coefficient of determination (R2) and the percentage of bias (PBIAS)) and the visual appreciation of hydrographs for monthly series. The statistical indices appear satisfactory with a NS and R2 ≥ 0.6 both for calibration and validation, and a PBIAS of -11.2 and -3.8 respectively for calibration and validation. The hydrological modeling of Loka basin has shown the impact of climate change already reported by some authors as well as anthropization. Thus, while the reservoir records a decrease in its water volume estimated at 384,604 m3 each year, the water demand undergoes an increase of 122,033 m3 per year.