Saturday 17 November 2018

Thirteen confirmed deaths as Cyclone Gaja makes landfall in Tamil Nadu, India.

Thirteen people have been confirmed dead, and it is feared that more that thirty have actually died, after Cyclone Gaja made landfall in Tamil Nadu State, India, on the morning of Friday 16 November 2018. Over 80 000 people have been evacuated from low lying areas of Nagapattinam, Pudukkottai, Tiruvarur, Thanjavur and Cuddalore districts in Tamil Nadu, as well as Karaikal and Puducherry districts in Puducherry ahead of the floods, though most of the deaths are thought to have been caused by high winds pushing over buildings and trees. The storm has caused extensive damage to the region's electricity distribution network, as well as blowing away 200 000 tones of salt collected from the Vedaranyam salt pans (an annual harvest resulting from the inundation of the low-lying area with seawater during the Summer Monsoon).

Damage caused by Cyclone Gaja in Nagapattinam District, Tamil Nadu. Press Trust of India.

Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

The path and strength of Cyclone Gaja. Thick line indicates the past path of the storm (till 6.00 am GMT on Saturday 17 November 2018), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at 12, 24, 36 and 72 hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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