Human contribution to atmosphere-ocean thermodynamic factors affecting the intense tropical cyclones over the Arabian Sea during the post-monsoon season

Abstract

Global warming and its implications for extreme events are important subjects of discussion worldwide. This study analyzes the changes in intense tropical cyclone (INT TC) activities over the Arabian Sea Basin (ARB) from 1981 to 2020 during the October–November season, along with its connection to the rise in thermal energy stored in the upper ocean and column-averaged atmospheric instability of the troposphere. The observations revealed that the frequency and intensity of TCs significantly increased owing to enhanced tropical cyclone heat potential (TCHP) and moist static energy (MSE), as eventually linked to the rise in sea surface temperature (SST). The increased availability of thermal energy in the ocean and the enhanced deep convection in the atmosphere make ARB more conducive to INT TCs. To quantify the human contribution to these observed changes, we employed a comparative analysis of the responses of environmental variables to individual forcing factors—greenhouse gas (GHG), aerosols, natural (solar and volcanic activities), and combined forcing of all these (ALL)—using CMIP6 multi-model simulations. The results bring the anthropogenic GHG forcing to the fore as an emerging driver in contributing to the increasing trends in SST, MSE, and TCHP, with no other individual forcing significantly accounting for the increasing trend in these background variables. Additionally, this human-induced warming increased the area enclosed by the threshold value of TCHP (70 kJ cm⁻²) and SST (28 °C) in the ARB, and hence made the ARB conducive to the genesis of INT TCs. Considering the large population in the coastal regions in the ARB and casualties related to historical TC disasters, the generation of more violent TCs in the ARB requires urgent attention. The substantial influence of anthropogenic GHG emissions on the increased activity of INT TCs over the ARB mandates better planning of climate change mitigation strategies.