Future Projections of Marine Heatwaves in the Northern Indian Ocean Using the <scp>HighResMIP</scp> Models: Role of Horizontal Resolution and Percentile Thresholds

ABSTRACT The marine heat wave (MHW) events are characterised in terms of duration, maximum intensity, and frequency of events. This study uses the High Resolution Model Intercomparison Project (HighResMIP) simulations to investigate how the horizontal resolution and percentile thresholds used to define the MHWs influence the characteristics of these events over the northern Indian Ocean region around the Arabian Sea (AS) and Bay of Bengal (BoB). It is shown that the simulation of the MHW characteristics improves with an increase in the model's horizontal resolution. The MHW events in the AS region tend to be less frequent but of longer duration (10%–25%) as compared to the BoB region. Further, the MHW events obtained using the 99th percentile threshold will be of shorter duration (30%–50%) and higher intensity (70%–75%) as compared to the 90th percentile threshold event. It is demonstrated that the duration, maximum intensity, and frequency of the MHW events will increase up to 75%, 35%, and 98%, respectively in the future projections under the SSP5‐8.5 scenario depending on the model and percentile threshold. It is also shown that the severe and extreme MHW events that were absent during the historical periods are projected to significantly increase in the near future. Such events will be more frequent and of longer duration under the global warming scenario. However, there exists a considerable inter‐model variability in the depiction of these projected changes, which introduces uncertainty in the estimation of the future risks and impacts of MHW events, thereby posing greater challenges for the adaptation and mitigation strategies.