Comparison of Two Model Approaches to Investigate Hydrological Processes in Five Selected Catchments in the Upper Blue Nile River Basin, Ethiopia.
No Thumbnail Available
Date
2011-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
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
Description
Keywords
Catchments, Upper Blue Nile River Basin, Hydrological Processes