Predicting the daily flow in ungauged catchments of the eastern part of the upper Blue Nile basin, Ethiopia

Estimation of stream flows is required as a prerequisite for solving several engineering and environmental problems. Applying regionalization techniques for ungauged or poorly gauged river basins to predict stream flows is one of the various approaches. This paper deals with predicting daily discharge at ungauged catchments using the conceptual lumped rainfall–runoff model HBV-96 in the eastern part of the upper Blue Nile basin. Model parameters were calibrated and validated using observed data, and sensitivity analysis of the model parameters was performed. The runoff coefficient (Beta), recession coefficient of the upper reservoir zone (Khq), the limit for evapotranspiration (LP), field capacity (Fc), percolation (Perc), and capillary rise coefficient (Cflux) are more sensitive than others. The model performance results show that of 20 gauged rivers, 9 of them have good agreement and distribution between the observed and simulated discharges. Moreover, transferring of gauged catchment model parameters into ungauged catchments was conducted using a regional model, sub-basin mean, area ratio, and spatial proximity methods. As a result, the regional model method is selected and recommended for predicting discharge for ungauged catchments.