Comparison of Two Model Approaches to Investigate Hydrological Processes in Five Selected Catchments in the Upper Blue Nile River Basin, Ethiopia.

No Thumbnail Available



Journal Title

Journal ISSN

Volume Title


Addis Ababa University


The successful application of hydrologic models depends not only on the model structure, the different time and space scale associated, but also on the accuracy of the simulated discharge. The key issue for operational users of hydrologic models is whether physically-based distributed models perform sufficiently better than conceptual models to justify the increased time and effort required for their application. The main objective of the research was comparison of two modelling approaches using on one hand quasi-semi-distributed conceptual model HBV–Light and on the other hand spatially distributed hydrologic model ArcSWAT. These models were applied to five test catchments representing wide variability in geographic location, climatic condition, areal extent and physiographical characteristics located in the Upper Blue Nile River Basin. The automatic calibration methodology, which is used in this study, applied a hierarchy of three techniques, namely screening, parameterization, and parameter sensitivity analysis, at the parameter identification stage of model calibration. Operating in continuous river-flow simulation mode, to demonstrate their effectiveness, a split-sample test was applied to the test catchments using a number of performance evaluation criteria. The monthly Auto-calibration and Validation results show that with increasingly secured efficiency the two models can equivalently capture monthly and seasonal flow patterns. This finding justifies that there is no significant benefit in applying the spatially-distributed model and that the simpler conceptual models would provide acceptably better simulations for monthly and seasonal flows. From calibration and validation results on daily time step, the performance of the SWAT is clearly not as good as the HBV model. In the case of SWAT daily discharge generally, however, showed less accurate simulation with some major discrepancies, which is a common attribute shared by many other studies, and r² of only less than 0.6 and Nash-Sutcliffe efficiency NSE of only less than 0.5 automatically were observed for all test catchments. This study confirms that simpler models for continuous river-flow simulation can surpass their complex counterparts in performance. There is a strong justification, therefore, for the claim that increasing the model complexity, thereby increasing the number of parameters, does not necessarily enhance the model performance. It is suggested that, in practical hydrology, the simpler models, “based largely on exercises in pattern recognition and curve fitting, through analysis of the available data” (O’Connor, 1998), can still play a significant role as effective simulation tools, and that performance enhancement is not guaranteed by the adoption of complex model structures. ii



Catchments, Upper Blue Nile River Basin, Hydrological Processes