Monday 7 October 2013

At least two dead as Typoon Fitow makes land in Fujian Province, China.

Two people are known to have died and several more are missing after Typhoon Fitow made landfall in Fujian Province, China, at about 1.15 am local time on Monday 7 October 2013 (about 5.15 pm on Sunday 8 OCtober GMT), bringing with it widespread flooding, up to 200 mm of rain and winds of up to 151 km per hour. Around 574 000 people have been evacuated from their homes in Fujian and Zhejiang Provinces in anticipation of the storm, and around 65 000 boats ordered to return to harbour. In addition many flights and rail services have been cancelled and public facilities in coastal areas closed down.

A wave breaking over sea defenses in Zhejiang Province. Getty Images.

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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