Monday 18 November 2013

Around 300 believed to have died in flooding after Tropical Cyclone Three hits Somalia.

Around 300 people are believed to have died after Tropical Cyclone Three hit the semiautonomous Puntland region of northeast Somalia on the weekend of 9-10 November 2013. The storm triggered widespread flooding in the low-lying region, which forms the tip of the Horn of Africa. Most of those dead are believed to have drowned as their homes were inundated, though a number of fishing vessels are also missing. A further 50 000 people are believed to have been displaced from their homes and are described as in need of 'urgent assistance'; though it is unclear what help they will get, as after two decades of bloody civil war few outside agencies are operating in Somalia and the local government has extremely limited resources with which to provide assistance.

Flooding in Puntland in the aftermath of Tropical Storm Three. Abdiqani Hassan/Reuters.

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 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.

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