Natural Disasters : Tropical Cyclones

Definition and Condition Required for Formation

• Definition: Tropical cyclones are intense circular storms that originate over warm tropical oceans and are characterized by strong winds, heavy rainfall, and low-pressure centers.
• Condition For Formation
  • Sea Surface Temperature: Must be at least 27°C or higher.
  • Coriolis Force: Essential for cyclonic rotation; absent near the equator (5° latitude).
  • Low-Pressure Area: A pre-existing low-pressure disturbance is needed.
  • High Humidity: Enhances cloud formation and precipitation.
  • Weak Vertical Wind Shear: Allows the storm structure to remain intact.
  • Upper-Level Outflow: Helps in the development of the system.
• Seasons
  • Pre-monsoon (April – June)
  • Post-monsoon (October – December)

Distribution of Cyclone 

• About 10 percent of the World’s tropical cyclones affect the Indian coasts.
• More cyclones occur in the Bay of Bengal than in the Arabian Sea.
• In India, tropical cyclones occur in the months of May-June and October-November.
• Four states (Tamil Nadu, Andhra Pradesh, Odisha, and West Bengal), one UT (Puducherry) on the east coast, and one state (Gujarat) on the west coast are highly vulnerable to cyclone disasters.

Classification of Tropical Cyclone

• Low-pressure Area: Wind Speed does not exceed 31 km per hour.
• Depression: Wind Speed between 31- 49 km per hour.
• Deep Depression: 50-61 km per hour.
• Cyclonic Storm: 62-88 km per hour.
• Severe Cyclonic Storm: 89-117 km per hour.
• Very Severe Cyclonic Storm: 118-167 km per hour.
• Extremely Severe Cyclonic Storm: 168-221 km per hour.
• Super Cyclonic Storm: 222 km per hour and higher.

Naming of Cyclones

1. Who Names Tropical Cyclones?
   • Cyclones are named by regional meteorological bodies following WMO (World Meteorological Organization) guidelines.
   • Different regions have different naming conventions:
     • North Atlantic & Eastern Pacific – Named by the National Hurricane Center (NHC).
     • Western Pacific – Named by the Japan Meteorological Agency (JMA).
     • North Indian Ocean (Bay of Bengal & Arabian Sea) – Named by IMD (India Meteorological Department).
2. Tropical Cyclone Naming System in India & Indian Ocean Region
   • In 2004, WMO and ESCAP (Economic and Social Commission for Asia and the Pacific) adopted a rotating list of names.
   • 13 member countries contribute names: India, Bangladesh, Pakistan, Sri Lanka, Maldives, Myanmar, Oman, Thailand, Iran, UAE, Yemen, Qatar, and Saudi Arabia.
   • Each country submits a list of names in advance.
   • Names are used sequentially, and once a name is used, it is removed from the list.
3. Rules for Naming Cyclones
   • Should be short, easy to remember, and culturally sensitive.
   • Must not be offensive or controversial.
   • Cannot be repeated once used.
   • Should be neutral in terms of politics, religion, and gender.

Governmental Initiatives for Cyclone Management in India

1. National Cyclone Risk Mitigation Project
   • India initiated this project to undertake structural and non-structural measures to mitigate the cyclone’s effects.
   • The project aims to protect vulnerable local communities from the impact of cyclones and other hydro-meteorological calamities.
2. Integrated Coastal Zone Management (ICZM) Project
   • The draft plan will dictate how prospective infrastructure projects would be assessed for clearance by laying out guidelines for coastal States.
3. Colour Coding of Cyclones
   • It is a weather warning that is issued by the India Meteorological Department (IMD) to alert people ahead of natural hazards.
   • The four colours used by IMD are Green, Yellow, Orange, and Red.