A Study on the Impacts of the Changjiang Diluted Water (CDW) on Surface Warming in the East China Sea using the MOHID in Summer, 2024

The Changjiang River discharges substantial freshwater into the East China Sea, forming the Changjiang Diluted Water (CDW), a low-salinity plume that influences regional hydrography, nutrient distribution, and marine ecosystems. CDW intrusions into Korean coastal waters can cause abrupt salinity and temperature changes, impacting fisheries and promoting harmful algal blooms. Climate change-driven variations in precipitation have altered CDW discharge patterns, increasing uncertainties in its behavior and impacts on marine environment. In this study, numerical simulations were used to assess CDW propagation and its influence on hydrographic properties of neighboring seas during the summer of 2024 using the MOHID (Modelo Hidrodinâmico) model. To investigate the influences of the CDW, we conducted two distinct numerical simulations. The first experiment was simulated with the original Chanjiang discharge, allowing CDW plume to enter the seas adjacent to the Changjiang River. In the second experiment, Changjiang outflows was capped at 30,000 m³/s, thereby limiting the freshwater flux from the CDW into the study area. As a result, on July, a significant impact of the CDW on both surface temperature and salinity in the study area. The temperature anomalies reached up to 2 ℃, while salinity decreased by as much as 4 psu. It indicates the strong influence of CDW on surface hydrography. The cross-sectional analysis revealed the influences of the CDW. A distinct halocline was observed due to the low-salinity plume in the upper 20 meters, and it might lead to surface warming while subsurface cooling due to suppressed vertical mixing. These results highlighted the considerable influence of the CDW on both horizontal and vertical hydrographic properties of the neighboring seas. Therefore, continued monitoring and numerical modelling approach to those low-salinity water plumes are essential to anticipate and mitigate potential ecological and economic impacts.