Syllabus: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.,
Context
- Cyclonic disturbances over the North Indian Ocean have changed markedly during the last century.
- Region includes the Arabian Sea, Bay of Bengal, and intervening land areas.
Trend 1: Long-term Change in Cyclonic Frequency
- Annual cyclone numbers show volatility, necessitating 10-year rolling averages for trend detection.
- Between 1900–1920, average disturbances remained below 10 per year.
- Disturbances surged to over 15 by the 1930s, staying elevated till the 1970s.
- Sharp decline occurred during the 1980s–1990s, reaching a low of eight in the 2000s.
- Activity rebounded during the 2010s–2020s, but remains below mid-century peaks.
Trend 2: Regional Shift in Cyclone Genesis
- Decline in total disturbances is driven mainly by reduced Bay of Bengal activity.
- Bay of Bengal remains the primary cyclone source but shows long-term weakening output.
- Arabian Sea disturbances have increased, partially offsetting the overall decline.
- Despite growth, Arabian Sea cyclone frequency remains lower than the Bay of Bengal.
- Regional imbalance significantly alters spatial cyclone risk distribution.
Trend 3: Intensification of Cyclonic Severity
- Disturbances increasingly intensify into severe cyclonic storms or higher categories.
- Share of severe storms in the Bay of Bengal has risen since the 1970s.
- Arabian Sea disturbances historically show higher intensification probability.
- Rising Arabian Sea activity combined with higher severity increases regional hazard exposure.
- Warmer sea surface temperatures provide more energy, strengthening cyclones.
- Arabian Sea is warming faster than average, increasing unpredictability and storm strength.
Trend 4: Shift in Seasonal Timing
- Cyclone genesis timing has shifted significantly in the Bay of Bengal.
- Earlier decades saw peak disturbances during July–September monsoon period.
- Post-1980s, majority of disturbances now originate during October–December.
- Late-season storms pose challenges for disaster preparedness and response planning.
- Seasonal shift increases vulnerability during post-monsoon coastal activities.
Conclusion
- Fewer storms now form, but those that do are stronger, later, and riskier.
- Combined frequency, intensity, regional, and seasonal shifts reshape North Indian Ocean cyclone dynamics.
- These trends demand revised forecasting, coastal planning, and disaster management strategies.