Context: Cyclone Fengal, a low-intensity storm (75-95 kmph) made landfall near Puducherry on November 30. However, the cyclone left a trail of destruction killing people, damaging numerous properties and standing crops over large areas.
Relevance of the topic:
Prelims: Key facts on Cyclones; conditions for formation.
Mains: Impact of climate change on cyclones.
What is a Tropical Cyclone?
- A tropical cyclone is a type of low-pressure weather system that forms over tropical or subtropical waters.
- They are characterised by strong winds, heavy rainfall, and a low-pressure centre.
- Tropical cyclones are known by different names depending on their location such as:
- Hurricanes in the Atlantic and north-eastern Pacific
- Willy-willy in North West Australia
- Typhoons in the northwest Pacific
- Cyclones in the South Pacific and Indian Ocean.
What are the conditions required for their formation?
- Warm water: Tropical cyclones form over warm tropical or subtropical waters with a surface temperature of at least 26.5°C. Warmth of water provides energy needed to fuel the storm.
- Moist air: Tropical cyclones require moist air to form. Moisture provides fuel for thunderstorms that make up the storm.
- Low wind shear: It allows the storm to maintain its organisation and strength.
- Pre-existing weather disturbance: Tropical cyclones typically form from pre-existing weather disturbances, such as an area of low pressure. These disturbances provide initial rotation and organization needed for a tropical cyclone to form.
- Converging winds: Tropical cyclones form in areas where winds are converging and rising, this allows for the development of thunderstorms and the low-pressure area that is the tropical cyclone.
- Coriolis force: It helps the wind to rotate. This is the reason that cyclones are not formed at the Equator.
All these conditions have to be met and be in the right balance, otherwise it would lead to the tropical cyclone dissipating, or fail to form.
What are the different categories of Cyclones?
- The India Meteorological Department (IMD) categorises cyclones based on the associated wind speeds. These categories are:
- low pressure (< 31 kmph)
- depression (31-49 kmph)
- deep depression (50-61 kmph)
- cyclonic storm (62-88 kmph)
- severe cyclonic storm (89-117 kmph)
- very severe cyclonic storm (118-221 kmph)
- super cyclone (222 kmph).
What is Cyclone Fengal?
- Fengal is a tropical cyclone which originated in the Bay of Bengal.
- Low-intensity cyclonic storm (75-95 kmph)
- It triggered exceptionally heavy rain (~500 mm in 24 hours) and flooding in Tamil Nadu and Puducherry.
Why did Cyclone Fengal cause widespread destruction despite being a low-intensity storm?
- According to the IMD, this happened primarily due to the movement of Cyclone Fengal.
- From its genesis to landfall, Fengal moved at a slow pace. On occasions, it moved at speeds slower than 6 kmph while at sea.
- Fengal also remained stationary for nearly 12 hours soon after making landfall close to Puducherry.
- Maintaining its intensity as a cyclone, the storm caused heavy rainfall and rough windy conditions over the region.
- Usually, cyclones weaken after landfall as they hit obstructions and experience friction from buildings and trees. In the case of Fengal, as the storm stayed stationary, and so the destruction was far more pronounced.
What is the impact of climate change on cyclones?
According to the Council on Energy, Environment and Water (CEEW) India, in the last 50 years, has recorded a 12-fold surge in the number of associated cyclonic events such as extreme rainfall, floods, sea-level rise, and thunderstorms.
- Increased sea surface temperature: Over the past 50 years, the global ocean has absorbed 90% of the excess heat generated due to man-made climate change leading to higher convection and rapid intensification of cyclones.
- Rising sea level: On account of Antarctic melting has increased the moisture availability for cyclones.
- Micro-climatic changes on land: Local heating of coastal land is pulled by adjacent oceans further heating it up.
- Changing weather events: El-Nino and rising marine heat waves lead to prolonged warm periods over oceans by reducing the ocean upwelling..
- Higher Atmospheric moisture: Anthropogenic global warming increases cyclonic precipitation rates, thereby increasing the frequency.
- Changes in wind systems: Occasionally intense winds drive the low-pressure regions to other areas, raising the frequency in those areas. E.g., The Gulab cyclone shifted to the Arabian sea from B.O.B.
