Revealing Enhanced Signals of Future Marine Heatwave Changes in the East/Japan Sea Through a High‐Resolution Dynamical Downscaling Ensemble

Abstract The East/Japan Sea (EJS) is a semi‐enclosed marginal sea that has experienced rapid sea surface temperature (SST) warming exceeding 0.9°C since the 1980s, which has intensified the occurrence of marine heatwaves (MHWs). Its semi‐enclosed nature amplifies the influence of external climate forcing, making reliable projections of future SST and MHW changes essential for assessing ecological and socio‐economic impacts. Here, we investigate future SST and MHW changes using high‐resolution (1/8°) dynamical downscaling simulations based on the Regional Ocean Modeling System (ROMS), driven by seven Coupled Model Intercomparison Project Phase 6 (CMIP6) models under four Shared Socioeconomic Pathway scenarios (SSP1‐2.6, SSP2‐4.5, SSP3‐7.0, and SSP5‐8.5) for 1982–2100. The ROMS ensemble outperforms the CMIP6 ensemble in reproducing observed SST and MHW characteristics for the historical period of 1985–2014, particularly during winter, due to improved simulation of the transport of the Tsushima Warm Current (TWC) through the Korea Strait and associated regional circulations. Future projections (2071–2100) indicate that SST warming and MHWs in the central EJS will become stronger, longer‐lasting, and more spatially heterogeneous in ROMS, in contrast to the more uniform patterns projected by CMIP6, especially under high‐emission scenarios. This spatial heterogeneity is associated with intensified transport of the TWC and a strengthened East Korean Warm Current, which enhance heat advection along their pathways into the basin interior. These results highlight the added value of high‐resolution dynamical downscaling for understanding and preparing for future SST and MHW changes in the EJS, providing insights for regional climate impact assessment and adaptation planning.