An operational real-time forecasting system for estuarine hydrodynamics: the Guadalquivir Estuary (SW Iberian Peninsula)

Abstract Accurate, real-time hydrodynamic forecasts are essential for understanding and managing short-term variability in estuarine systems. This study presents an operational real-time forecasting system for the Guadalquivir Estuary (SW Iberian Peninsula), a highly modified and regulated estuary of strong scientific and operational interest. The system is built on a three-dimensional Delft3D-Flow model that integrates, every 12-h, (i) astronomical and meteorological tide at the ocean boundary; (ii) regulated freshwater dam and tributary releases; and (iii) wind and surface heat-flux fields. Each operational cycle performs a 36-h hindcast followed by a 72-h forecast, completing the full 108-h integration in less than 25 min on a 24-core workstation. Validation against seven tide gauges during 2024 shows high predictable skill, with peak water level errors below 15 cm along the entire estuary and below 10 cm in the navigable reach, 6–10% of the tidal range, while Pearson correlations exceed 0.95. No systematic timing drift is detected between successive forecast cycles. Sensitivity tests show that the pragmatic treatment of unknown future forcings adds less than 4 cm to forecast error, well within the intrinsic model uncertainty. An automated alert protocol monitors forecast skill in near real time, supporting operational robustness. Overall, the system delivers reliable three-day water level predictions, demonstrating how numerical modeling, real-time validation, and uncertainty management can be combined to support operational oceanography in tidally dominated estuaries, with potential transferability to other estuarine systems worldwide.