Assessing anthropogenic thermodynamic influences on marine heatwaves near the Korean Peninsula using a coupled regional climate model

Marine heatwaves (MHWs), particularly high-water temperature events during summer, are becoming more frequent, intense, and widespread due to global warming. Rapid ocean warming around the Korean Peninsula (KP), exceeding rates in the East Asian marginal seas and the global average, highlights the need to better understand anthropogenic thermodynamic influences on regional MHWs. This study evaluates the deterministic thermodynamic sensitivity of selected MHW cases near the KP to a CMIP6-derived climatological anthropogenic thermodynamic perturbation using a regional coupled modeling framework with the Weather Research and Forecasting (WRF) and Regional Ocean Modeling System (ROMS). Two experiments were conducted for the four selected MHWs: the CTL experiment, representing the factual world, and the NAT experiment, representing a counterfactual world in which the imposed climatological anthropogenic thermodynamic signal was removed. The anthropogenic thermodynamic perturbation is estimated as the difference between the historical-nat (natural forcings only) and historical-all (natural + anthropogenic forcings) simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) over 1985–2014. During the 12–25 August analysis period, the CTL–NAT differences in regional median daily sea surface temperature (SST) range from 0.30 to 0.83 °C in the Yellow Sea, South Sea, East Sea (Sea of Japan), and Jeju coastal waters. Averaged over the four cases, the number of MHW days, MHW intensity, and spatial extent were larger in CTL than in NAT by 1.17–2.10 days, 0.15–0.18 °C, and 6.58–25.78 percentage points, respectively. Within-window duration was also generally longer in CTL than in NAT. These results indicate that the selected MHW cases are sensitive to the imposed anthropogenic thermodynamic perturbation, although the magnitude of the response varies by region and event.