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Why low-intensity Cyclone Fengal caused large-scale destruction

According to the IMD, this happened primarily due to the movement of Cyclone Fengal.

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Flood-hit area in Villupuram, Tamil Nadu on December 2. PTI

Cyclone Fengal, which made landfall near Puducherry on November 30, was a low-intensity storm as it maintained a wind speed of about 75-95 kmph. However, the cyclone left a trail of destruction in its wake. At least 12 people died, mostly in Tamil Nadu, numerous properties were damaged, and standing crops were destroyed over large areas.

Why did Cyclone Fengal cause widespread destruction despite being a low-intensity storm?

First, 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), and super cyclone (> 222 kmph).

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How did Fengal compare to past cyclones?

Over the years, Indian coasts have witnessed several severe storms which led to large-scale devastation. Associated maximum wind speeds went up to 260 kmph (Odisha super cyclone, October 1999), 215 kmph (Cyclone Phailin, May 2013), and 185 kmph (Cyclone Amphan, May 2020). Therefore, compared to many earlier storms, Cyclone Fengal was a low-intensity storm.

What was the impact of Fengal?

Fengal triggered exceptionally heavy rain and flooding in Tamil Nadu and Puducherry.

Krishnagiri and Villupuram in north Tamil Nadu, close to where Fengal made landfall, were among the worst affected areas between November 29 and December 1. Mailam village in Villupuram received 510 mm of rainfall in 24 hours. Puducherry received 490 mm of rainfall in a day, breaking the previous record of 211 mm set on October 31, 2004.

Air, rail and road transport took a hit, highways were inundated, and lakes and rivers overflowed.

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Why was Fengal so destructive?

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, after landfall, cyclones weaken as they hit obstructions and experience friction from buildings and trees. In the case of Fengal, as the storm stayed stationary, the destruction was far more pronounced, leading to numerous deaths.

Notably, during recent cyclones (such as Dana in October this year), which were more intense than Fengal, human casualties were either nil or limited to single digits.