The future projection of cyclones in Bay of Bengal: a study using coupled ocean atmosphere model

In this study, the behaviour of cyclones in the Bay of Bengal in future climatic conditions is analysed with the help of an ocean-atmosphere coupled model. The weather research and forecasting (WRF) model is coupled with the regional ocean modelling system (ROMS) using a model coupling toolkit in the framework of coupled ocean atmosphere wave sediment transport (COAWST) modelling system. The pseudo global warming (PGW) methodology is used to project the cyclones to future climatic (2075) conditions for Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. The present study considered two cyclones, namely extremely severe cyclonic storm Phailin (2013) and very severe cyclonic storm Titli (2018). The results show that the coupled model well captured the behaviour of cyclones in the atmosphere and the ocean. Compared to the current conditions, the maximum sustainable wind speed increases by 7.2 km/h for both cyclones for the RCP 8.5 scenario in far future (2075). The accumulated cyclone energy (ACE), power dissipation index (PDI) and precipitation increase in future climatic condition. The increase is more significant for RCP 8.5 compared to RCP 4.5 scenario. The cyclone damage potential (CDP) too increases in future climates, the increase is 25% and 113% for RCP 8.5 scenario for cyclone Phailin and Titli respectively. The cyclones intensify more in the future than current conditions due to the combined effect of increased upper ocean heat content (UOHC) and reduced translation speed. In future, during the passage of cyclones, the UOHC is seen to reduce more, which indicates that more energy is transferred from the ocean to the atmosphere. The analysis of the UOHC, the moisture content in the atmosphere, and the atmospheric instability in future conditions show that the atmospheric and ocean conditions are more favourable for the formation of intense cyclones in the future.