Future projection of marine heatwaves in a global marine hotspot: case of East/Japan sea

The East Sea/Japan Sea is one of the regions where ocean warming is the fastest. Selecting the best Global Climate Models (GCMs) specific to the East Sea is a crucial step in reducing uncertainty related to GCM simulations when studying the future projections of marine heatwaves (MHWs). This study identifies the best models that simulate the MHW metrics of frequency, maximum intensity, and duration in the East Sea by evaluating their performance at each grid level. The models were assessed using performance indicators of bias (BIAS) and interannual variability skill score (IVS) with reference to the National Oceanic and Atmospheric Administration (NOAA) dataset. A group decision-making approach was used to rank the models based on their grid-wise performances. Most models showed shortcomings in the simulation of MHW duration compared to that of frequency and maximum intensity. The best performing GCMs from the Coupled Model Intercomparison Project sixth phase (CMIP6) for this area were identified as NorESM2-MM and GFDL-ESM4. Based on the top-ranked approach, these two models were selected for the multi-model ensemble (MME) to analyze the future MHWs in the East Sea. The MME underestimated the frequency and maximum intensity but overestimated the duration for the historical period (1985–2014). The shifting baseline approach was employed for the future projection of MHWs during the near future (2041–2070) and far future (2071–2100) under four Shared Socioeconomic Pathways (SSPs). The projected future changes relative to the historical period suggest a potential increment of MHW frequency and maximum intensity more in the near future compared to that of the far future. In the near future, all the scenarios indicate an increment of frequency (SSP1-2.6: 7.9%, SSP2-4.5: 3.0%; SSP3-7.0: 7.9%; SSP5-8.5: 8.3%) and maximum intensity (SSP1-2.6: 7.5%, SSP2-4.5: 6.9%; SSP3-7.0: 6.2%; SSP5-8.5: 8.7%) compared to the historical period. The spatial analysis of the future changes indicates that certain regions are more vulnerable to changes, and these regions are important in the fisheries and ecosystems.