Sciency Thoughts: Twenty two confirmed deaths as Cyclone Ockhi sweeps across the Lakshadweep Archiapelago.

Saturday, 2 December 2017

Twenty two confirmed deaths as Cyclone Ockhi sweeps across the Lakshadweep Archiapelago.

Twenty two people have been confirmed dead after Cyclone Ockhi swept across the Lakshadweep Archipelago, part of the Indian State of Kerala, on Saturday 2 December 2017. The majority of the deaths occurred in the islands' coastal communities and fishing fleet, which has been scattered by the storm, with over 500 fishermen rescued by vessels from the Indian Navy. Coastal communities and fishing vessels from the Keralan mainland have also been badly hit, as have those in Tamil Nadu and Sri Lanka, where at least seven people have died.

Storm damage in Kanyakumari District, Tamil Nadu following the passage of Cyclone Ockhi. European Commission/Flickr.

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 passage of Cyclone Winston till 07.00 GMT on Tuesday 28 March 2017 (thick line) with its predicted future path (thin line, circles represent the margin of error on the predictions). Colours indicate the strength of the storm. Tropical Storm Risk.

The low pressure above tropical storms causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas, while at the same time the heat leads to high levels of evaporation from the sea - and subsequently high levels of rainfall. This can cause additional flooding on land, as well as landslides, which are are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.