Double intensification centers of summer marine heatwaves in the South China Sea associated with global warming

Marine heatwaves (MHWs) in the South China Sea (SCS) have prolonged impacts on local ecosystems and economies, and accurate projection of MHWs under future global warming is crucial for the high-quality development of local society. The future change in the spatial pattern of MHWs, however, is not clear despite the well-known overall intensification of MHWs. Here we find that the Coupled Model Intercomparison Project Phase 6 (CMIP6) models can effectively capture the main distribution of observed SCS MHWs, showing a uniform distribution of frequency and a "north high-south low" distribution of mean intensity and cumulative intensity. However, it is worth noting that the simulated center of long MHW duration is shifted to the southern SCS compared to the central SCS in observations. Under the Shared Socioeconomic Pathway 1-2.6 (SSP126) scenario, the increase in MHW cumulative intensity exhibits a double-center structure in the northern coastal region and southern SCS. This is primarily attributed to the large increase in frequency and mean intensity in the north, and an increase in duration in the south. Both the SSP245 and SSP585 scenarios project similar patterns of MHW intensification, but with larger magnitudes. The climatological distribution of the mixed layer depth (MLD), which is deeper in the south and shallower in the north, contributes to the spatial distribution of SCS MHW changes. The strong seasonal-mean sea surface temperature (SST) warming in the northern SCS, caused by enhanced solar radiation, also contributes to the intensification of MHW frequency and mean intensity in the northern region.