An operational forecast system for the intrusion of the Changjiang River plume into the northern East China Sea

The presence of unusually low-salinity water from the Changjiang River (CR) poses a significant marine environmental threat in the East China Sea (ECS), disturbing aquatic habitats and ecosystems in surrounding countries’ waters. Demand for early warning of such threats by the fishing and aquaculture industries has been increasing in recent decades. This article introduces the Data-assimilative Regional Ocean Prediction system (DROPS), an operational forecasting system designed to predict the spatiotemporal behavior of low-salinity plumes in the northern ECS. DROPS is based on a regional ocean model with a four-dimensional variational data assimilation, covering the Yellow Sea and ECS shelves. This operational system runs automatically once a day, including a 72-hour hindcast and a 120-hour forecast, using initial conditions from the previous assimilation run. Predictions were compared with real-time measurements from weather buoys, ocean research stations, and unmanned wave gliders. DROPS successfully captured the low-salinity and high-temperature water observed over the northern ECS during the summer of 2022, showing moderate skill in predicting salinity and temperature variations. Data assimilation decreased temperature and salinity errors by 27% and 22%, respectively, improving forecasting performance. Our prediction system provides essential information to support decision-making for issuing early warnings of low-salinity and high-temperature water events.