Validation of the Refined Daily Forecasting System for ALPS Treated Water Dispersion Against Observation Data near the Fukushima Outlet

Since the commencement of the ALPS-treated water discharge from Fukushima Daiichi on 23 August 2023, an operational forecasting system developed in Taiwan has been established to provide daily seven-day predictions of tritium dispersion in the North Pacific. The system integrates the real-time CWA-OCM with particle tracking and grid-based concentration diffusion modules, driven by hourly discharge data reported by TEPCO. The computational domain covers the Kuroshio–Kuroshio Extension and adjacent marginal seas, with refined resolution near the outlet to capture dispersion within approximately 3 km. Validation against TEPCO tritium monitoring data at 12 sites across three representative batches (1, 2 and 12) demonstrated that the system successfully reproduced both the spatial distribution and temporal evolution of tritium concentrations, with modeled maxima typically within the observed range of 10–20 Bq/L. However, the model slightly underestimated the peak values, and simulated concentrations decreased more rapidly than observed during the five-day post-discharge period. This discrepancy is likely attributed to the absence of the jet effect in the current model. Therefore, we will continue to refine the model and integrate these improvements into our operational forecasting system.