Hydrological predictions for small ungauged watersheds in the Sudanian zone of the Volta basin in West Africa

• Implementation of two hydrological models in the West African Sudanian climate zone
• Identification of the optimal range of a conceptual parameter of a hydrological model with three criteria of efficiency
• Use of the multiple linear regression modeland the kriging method to predict the conceptual parameters of the hydrological models
• Estimation of the annual water budgets for ungauged watersheds

Study regionHydrological observation networks in the West African region are not dense and reliable. Furthermore, the few available discharge data often present significant gaps. The Volta basin, the second largest transboundary basin in the region, is a typical example of a basin with inadequate hydrological networks.Study focusIn this study, a prediction approach to determine monthly discharge in ungauged watersheds is developed. The approach is based on the calibration of two conceptual models for gauged watersheds and an estimation of models’ parameters from the physical and climatic characteristics of the watersheds. The models’ parameters were determined for each ungauged watershed through two different methods: the multiple linear regressions and the kriging method. The two methods were first validated on five gauged watersheds and then applied to the three ungauged watersheds.New hydrological insights for the regionThe application of the two hydrological models on the eight watersheds helped to produce relevant monthly runoff and to establish the annual hydrological balances from 1970 to 2000 for both gauged and ungauged watersheds. The developed method in this study could therefore help estimate runoff time series, which are of crucial importance when it comes to design hydraulic structures such as small reservoirs.