Changing Trends in Cyclonic Disturbances

Summary of Cyclonic Disturbances in the North Indian Ocean

Trends in Cyclonic Disturbances

1. Frequency:

   • Historical data indicates a significant change in the frequency of cyclonic disturbances from 1900 to 2025.
   • 10-Year Rolling Average:
     • Early 1900s (1900-1920): Below 10 disturbances.
     • 1930s: Surged over 15 disturbances, leading to stability until the 1970s.
     • Declined sharply in the 1980s and 1990s, reaching a low of 8 in the 2000s.
     • Recent rebound in the 2010s, current levels still lower than mid-century peaks.

2. Origin of Disturbances:

   • Bay of Bengal: Primary cradle of disturbances, currently experiencing a decline in activity.
   • Arabian Sea: Increased activity noted, with fewer disturbances but a rising trend.

3. Intensity and Severity:

   • Disturbances have become more severe over the years.
   • Classification of disturbances:
     • Low-pressure area: Winds <31 kmph.
     • Depression: 31–49 kmph.
     • Deep Depression: 50-61 kmph.
     • Cyclonic Storm: 62-88 kmph.
     • Severe Cyclonic Storm: 89-117 kmph.
     • Very Severe: 118-166 kmph.
     • Extremely Severe: 167-221 kmph.
     • Super Cyclonic Storm: ≥222 kmph.
   • Notable increase in the percentage of disturbances that intensify to severe cyclonic storms.

4. Seasonality Changes:

   • Shift in origin of disturbances towards the fourth quarter (October-December) rather than traditional peak months of July-September since the 1980s.

Environmental Context

• Ocean Temperature:
  • The Arabian Sea is experiencing significant warming, which contributes to increased cyclone intensity and unpredictability. Warmer ocean temperatures provide more energy to tropical storms.

Data Sources

• The data presented is sourced from the Cyclone eAtlas by the India Meteorological Department, highlighting the scientific basis for the trends observed over the past century.

Implications

• The trends in cyclonic disturbances are crucial for disaster preparedness and response planning, indicating changing weather patterns that need to be addressed by government policies and climate adaptation strategies.
• Enhanced cyclone intensity and changes in seasonality can strain infrastructure and emergency services, requiring updates to existing disaster management frameworks.

Relevant Policies and Actions

• Governments may need to revise climate policies and disaster management protocols in response to shifting cyclone patterns, focusing on enhancing resilience and reducing vulnerabilities in affected regions.