The Pará-Amazon estuarine system encompasses a complex and dynamic region. This study investigates the impact of hydrological uncertainties related to discharge variability at the Óbidos gauging station and their influence on water level fluctuations at two downstream monitoring stations: Santana harbor and Belém harbor. The Santana harbor station (Amapá, Brazil) is located on the left bank of the North Channel of the Amazon River, while the Belém harbor station (Pará, Brazil) is situated on the right bank of the Pará River estuary. A hydrodynamic model was employed to support this investigation. The model domain covers approximately 169,400 km \(^{2}\) . Model calibration, validation, and verification were conducted using observed water level and discharge data. The model’s performance was evaluated based on statistical metrics, including Mean Absolute Error (MAE), Bias, Root Mean Square Error (RMSE), Nash-Sutcliffe Efficiency (NSE), and Magnitude Coherence Index (MCI). The model demonstrated satisfactory performance in all stages: calibration, validation, and verification. Following calibration, the impacts of discharge variations at Óbidos–ranging from ±6% during the wet season to ±20% during the dry season–were assessed. The results indicate that the water levels at Santana harbor are more sensitive to uncertainties in the Óbidos rating curve compared to Belém harbor. Nevertheless, the high RMSE observed at Santana harbor during the wet season, approximately 0.577 m, suggests that the calculated error during this period is likely not solely attributable to uncertainties in the Óbidos rating curve. Instead, it likely reflects other model limitations, such as bathymetric uncertainties, inaccuracies in tidal boundary conditions, or the omission of additional hydrodynamic processes that may influence the system’s behavior.
