Projected Future Changes in North Indian Ocean (NIO) Tropical Cyclones Simulated by High-Resolution Global Climate Models (GCMs)
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Using five HighResMIP GCMs at ∼25 km resolution, we examine projected future changes in tropical cyclone (TC) activity under a warmer climate and assess the role of large-scale environmental conditions. Projections for the Bay of Bengal (BoB) indicate a decline in TC frequency across all models (except MPI-ESM1.2 during the post-monsoon [October–November]), despite projected increases in sea surface temperatures (SST). The reduction is generally stronger in the pre-monsoon (April–May) season, whereas greater moistening in the post-monsoon is associated with a smaller decrease in TC frequency. In contrast, the Arabian Sea (AS) shows a moderate increase in basin-wide TC frequency, consistent with a westward shift in NIO TC tracks. While changes in the seasonal cycle of genesis indices (GPI, GPI2010, and VI) cannot fully explain the future seasonal cycle of TC frequency, the sign of the seasonal mean changes between pre- and post-monsoon generally agrees across most models. Decomposition of environmental terms in the genesis indices shows that the moist entropy deficit term is the most consistent driver of BoB TC reductions in a warmer climate, while decreases in relative humidity and low-level vorticity contribute more weakly and inconsistently. SST and potential intensity (PI) increases align with higher TC frequency over parts of the AS but fail to explain the projected BoB TC reduction, suggesting that other dynamic and thermodynamic factors also influence the initiation of organized convection in cyclogenesis. Overall, results suggest fewer but potentially stronger TCs in the NIO, with tropospheric moisture emerging as the dominant control.
