<p>This study generated synthetic streamflow for the ungauged Omo-Kuraz Dam watershed in the Omo-Gibe River Basin, southern Ethiopia, using the MIKE 11 NAM conceptual rainfall–runoff model. Due to the absence of direct gauged data at the dam site, the downstream Omorate gauging station was utilized for model calibration (2010–2016) and validation (2017–2020), after which the optimized parameter sets were transferred to the ungauged watershed. Sensitivity analysis evaluated nine core hydrological parameters. The model achieved strong predictive performance, yielding coefficient of determination R2 values of 0.84 and 0.80 and Nash–Sutcliffe efficiency (NSE) values of 0.67 and 0.59 during the calibration and validation phases, respectively. The resulting synthetic streamflow indicated a mean annual discharge of 324.16 m³/s for the Omo-Kuraz watershed, compared with 510.53 m³/s observed at the Omorate station. Comparative analysis revealed that the observed streamflow exhibits a highly regulated baseline ranging from 260 to 1436 m³/s due to upstream river management, whereas the simulated design runoff captures a wider natural hydrographic variability between 83 and 2224 m³/s. To enhance spatial precipitation representation across complex terrain, the high-resolution (0.05°) CHIRPS satellite dataset was integrated to verify gauge-based inputs and map orographic patterns originating in the northern highlands. While the synthetic records are subject to inherent uncertainties from unmodeled reservoir operations and rainfall interpolation, the outcomes demonstrate that the MIKE 11 NAM framework provides a highly practical tool for streamflow generation in data-scarce catchments, offering key baseline data for water resources planning in the Omo-Gibe Basin.</p>