Revisiting marine heatwaves baselines in warming oceans under nonstationary condition

Marine Heatwaves (MHWs) are prolonged episodes of above- 'normal' Sea Surface Temperature (SST) which have imposed detrimental impacts on oceans and their dependent ecosystem services. The key question still remained unresolved or at least still not fully addressed in MHW science, is 'What is a valid normal or baseline?'. In other words, can the conventional 'normal' serve as a realistic valid baseline in today's oceans experiencing the impacts of contemporaneous climatic changes and global warming during anthropogenic era? To robustly address this issue, we attempted to propose a methodology for identifying MHW thresholds that accounts for SST warming. In this study, we developed a novel, consistent, flexible and as realistic as possible working framework that practically deals with the current actual climate conditions which mainly involves incorporating the nonstationarity concept into the MHW definition. We presented our proposed approach using an exemplification exhibiting potential global implications. The competency of our proposed framework was evaluated by characterizing MHWs in one of the world's warmest marine environments, the Persian Gulf and Oman Sea. Our findings from employing dynamic non-stationary thresholds revealed that, MHWs have been merely evolving into a new warmer routine representing no significant variations in MHWs metrics except for the maximum SSTs during the extreme events.