Decadal Variability of Convective Instability and Bimodal Convection over the Indian Coasts Using ERA5 Reanalysis (2012-2021)

Convective activity over the Indian coastal region exhibits strong spatial and temporal variability due to complex interactions between land-sea thermal contrasts, monsoon circulation, regional topography, and large-scale climate drivers. In recent decades, accelerated warming of the Indian Ocean, increasing frequency of severe cyclonic disturbances, and the growing influence of modes such as the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) have further modified coastal convective environments. In this study, we investigate the decadal variability (2012–2021) of convective instability and bimodal convection over the Indian east and west coasts using high-resolution ERA5 reanalysis data.Six representative coastal stations-Kolkata, Bhubaneswar, and Chennai along the Bay of Bengal coast, and Gujarat, Goa, and Mumbai along the Arabian Sea coast-were selected to capture key longitudinal and latitudinal contrasts in convective regimes. The analysis integrates major thermodynamic indices, including Convective Available Potential Energy (CAPE), Total Totals Index (TTI), and K-Index, together with 2-m air temperature (T ₂ m) and total precipitation (TP), to examine seasonal, interannual, and dynamical characteristics of coastal convection.The results reveal a pronounced bimodal convective structure over both coasts, with a strong pre-monsoon instability peak driven by intense surface heating and a broader monsoon-post-monsoon peak associated with large-scale circulation and cyclonic systems. The east coast displays significantly higher instability (CAPE often exceeding 3000–4000 J kg⁻¹) and stronger thermodynamic control of convection, whereas the west coast experiences heavier rainfall despite lower instability due to dominant monsoon dynamics and orographic uplift along the Western Ghats. Interannual variability is strongly modulated by large-scale climate anomalies, with enhanced instability during the 2015 El Niño and altered moisture conditions during the 2019 positive IOD. The study period also encompasses several high-impact cyclones, which contributed to pronounced fluctuations in coastal convection and precipitation.The weak relationship between CAPE and rainfall, especially over the west coast, highlights that thermodynamic indices alone cannot explain precipitation variability under monsoon-dominated conditions. The findings emphasize the need to integrate thermodynamic instability, surface forcing, and large-scale dynamical processes to better understand and predict convective behavior over India’s densely populated coasts. This study provides new insights into the evolving nature of coastal convection in a warming climate and has important implications for regional severe weather forecasting and disaster preparedness.