ABSTRACT Graphical abstract showing the study area, model data inputs, ArcSWAT calibration and the model performance at the upper basin and main outlet. The Manavgat River Basin (Türkiye) is a significant case study for understanding semi-arid hydrological regimes under climate change and rising water demand. This study applied the Soil and Water Assessment Tool (SWAT) to test the suitability of the SWAT model in predicting hydrological processes in the basin. The daily weather and streamflow data were provided from the Turkish governmental agencies, alongside spatial data were integrated into the ArcSWAT model and calibrated using the RSWAT package. The finding demonstrated a strong model performance in the upper basin in Sinanhoca (Pbias = 9.02%, NSE = 0.75) with a p-factor ≥0.65 and r-factor ≤1.4. This success indicates the model can sufficiently simulate the streamflow and baseflow processes that dominate the headstreams. However, the model failed at the main outlet, presenting poor matrics (Pbias = −32%, NSE = 0.24, p-factor = 0.45, r-factor = 1.12) and a high streamflow underestimation. The model's failure was primarily due to inter-basin ungauged flow, anthropogenic and complex karstic subsurface flow structure. These findings serve as a roadmap for future research into systems-based modeling techniques that specifically take these important external hydrological inputs into account.
HALİMİ et al. (Tue,) studied this question.