Using a regionalisation approach to evaluate streamflow simulated by an ecohydrological model calibrated with global land surface evaporation from remote sensing

Abstract

Study regionWest Africa. Study focusThe objective of this study was to quantitively evaluate streamflow previously simulated by the Soil and Water Assessment Tool (SWAT) model in an ungauged basin (Ogun River) that was calibrated/validated using GLEAM (v3.0a) AET data (Odusanya et al., 2019). To evaluate this simulated streamflow in the ungauged Ogun River Basin, a gauged basin (Ouémé River) was selected based on proximity and on similar catchment attributes. Firstly, the non-unique parameter sets from the SWAT set-up in the ungauged Ogun River Basin were transferred to SWAT that was setup in the neighbouring gauged Ouémé River Basin (referred to as the regionalisation method). Secondly, the SWAT model in the Ouémé River Basin was setup by calibrating the model using the observed streamflow data (referred to as the conventional method). New hydrological insights for the regionIn the gauged Ouémé River Basin, using the conventional method, a higher streamflow performance was obtained for all non-unique SWAT simulations, compared with the regionalisation method. However, a satisfactory streamflow performance was obtained with the regionalisation method in the south of Ouémé River Basin (Save gauge: highest NSE = 0.79, R2 = 0.81, PBIAS = 2.1, KGE = 0.85) and at the Ouémé River Basin outlet (Bonou gauge: highest NSE = 0.79, R2 = 0.84, PBIAS = −4.5, KGE = 0.84) that had the most similar attributes to the Ogun River Basin. The study findings show that using satellite-based AET data to calibrate a hydrological model can lead to an acceptable model performance in ungauged basins. The regionalisation method was useful for assessing the simulated streamflow in the ungauged basin, especially when catchment similarity is ensured, and parameter non-uniqueness is applied. This research contributes to advancement in alternative means of modelling and evaluation of hydrologic model simulations in an ungauged basin.