African Journal of
Environmental Science and Technology

  • Abbreviation: Afr. J. Environ. Sci. Technol.
  • Language: English
  • ISSN: 1996-0786
  • DOI: 10.5897/AJEST
  • Start Year: 2007
  • Published Articles: 1082

Full Length Research Paper

Evaluating SWAT model for streamflow estimation in the semi-arid Okavango-Omatako catchment, Namibia

Negussie Kaleb Gizaw
  • Negussie Kaleb Gizaw
  • Department of Land and Spatial Sciences, Namibia University of Science and Technology, 13388 Windhoek, Namibia.
  • Google Scholar
Wyss Daniel
  • Wyss Daniel
  • Department of Cartography, GIS and Remote Sensing, Georg-August University Goettingen, 37077 Goettingen, Germany.
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Knox Nichola
  • Knox Nichola
  • Department of Land and Spatial Sciences, Namibia University of Science and Technology, 13388 Windhoek, Namibia.
  • Google Scholar
Vallejo Orti Miguel
  • Vallejo Orti Miguel
  • Department of Land and Spatial Sciences, Namibia University of Science and Technology, 13388 Windhoek, Namibia.
  • Google Scholar
Corral-Pazos-de-Provens Eva3
  • Corral-Pazos-de-Provens Eva3
  • Departamento de Ciencias Agroforestales, Universidad de Huelva, 21819 Huelva, Spain.
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Kappas Martin
  • Kappas Martin
  • Department of Cartography, GIS and Remote Sensing, Georg-August University Goettingen, 37077 Goettingen, Germany.
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  •  Received: 02 September 2022
  •  Accepted: 18 October 2022
  •  Published: 30 November 2022

Abstract

A semi-distributed hydrological model was used for runoff estimation in the Okavango-Omatako catchment in Namibia. The model was configured for a 31-year period from 1985 to 2015. Subsequently, calibration and validation processes followed using the SUFI-2 algorithm. For evaluating catchment simulation, two methods were used: i. model prediction uncertainty measured by P-factor and R-factor and ii. Model performance indicators, that is, Nash-Sutcliffe Efficiency (NSE), Coefficient of determination (R2), Percent bias (PBIAS), and Residual variation (RSR). The P-factor achieved 0.77 and 0.68 while R-factor attained 1.31 and 1.82 for calibration and validation, respectively. The following indicators were used to evaluate the model performance through calibration and validation results respectively; NSE with 0.82 and 0.80, R2 with 0.84 and 0.89, PBIAS achieving -20≤PBIAS≤-1.1 and RSR performing 0.42 and 0.44. All performance indices achieved very good ratings apart from PBIAS validation which rated as satisfactory. The semi-arid characteristics together with relatively flat terrain features justified the need for the evaluation of model performance using discharge data in our study region. SWAT demonstrated reasonable results in modelling semi-arid streamflow with high and low flows adequately captured. Consequently, this evaluation was necessary for further investigations into impacts of climate change on scarce water resources highlighting the challenges of SWAT model applications in our study area climatic regime and other similar regions globally for further model improvements.

 

Key words: Stream flow, catchment, semi-arid, SWAT, SUFI-2, calibration, TanDEM-X, Okavango, Namibia.