Introduction
Tropical cyclones originating in the Bay of Bengal and the Arabian Sea exert a profound influence on the Indian subcontinent. While their immediate impacts manifest as severe weather disruptions along the coasts, their cumulative occurrence shapes regional climate regimes, seasonal precipitation distribution, and monsoon dynamics.
1. Impacts on Short-Term Weather
Cyclones cause acute, rapid atmospheric changes over localized and regional extents within a span of days:
- Extreme Precipitation: Intense deep convection within the eyewall and spiral rainbands brings torrential downpours exceeding 20 cm in 24 hours, often triggering flash floods and inundating urban drainage systems (e.g., Cyclone Michaung, 2023).
- Gale Squalls and Wind Fields: Steep pressure gradients generate high-velocity winds often exceeding 150 km/h, abruptly modifying surface temperature, atmospheric pressure, and localized humidity profiles (e.g., Cyclone Fani).
- Storm Surges and Atmospheric Humidity: Marine storm surges measuring 3 to 5 metres drive saline sea water miles inland, elevating atmospheric humidity levels, inundating coastal lowlands, and altering coastal boundary layer conditions.
2. Impacts on Long-Term Climate and Seasonal Regimes
Beyond day-to-day weather anomalies, cyclonic activities actively modulate seasonal and macro-climatic patterns across India:
- Modulation of Monsoon Dynamics: Pre-monsoon cyclones in the Bay of Bengal can accelerate the northward advance of the Inter-Tropical Convergence Zone (ITCZ) and the monsoon trough. Conversely, early-season Arabian Sea cyclones can siphon equatorial moisture away from peninsular India, stalling the southwest monsoon's onset (e.g., Cyclone Biparjoy, 2023).
- Regional Precipitation Budgets: Post-monsoon cyclonic storms and depressions developed in the Bay of Bengal during October to December contribute nearly 50–60% of the total annual rainfall received by the Coromandel Coast, especially in coastal Tamil Nadu and Andhra Pradesh.
- Shifting Ocean-Atmosphere Climatology: Elevated sea surface temperatures (SSTs) driven by climate change have intensified cyclogenesis in the Arabian Sea, leading to altered regional moisture fluxes, increased atmospheric water-holding capacity, and changing aridity patterns across western India.
Conclusion
Tropical cyclones are not merely destructive disasters but integral drivers of India's hydro-meteorological balance. Enhancing coupled ocean-atmospheric modeling and incorporating cyclonic feedbacks into long-range seasonal forecasts under Mission Mausam will be crucial for national climate resilience.