Sunday 3 November 2013

Three dead and two missing as Typhoon Krosa sweeps across the north of Luzon Island.

Three people are known to have died and two more are still missing after Typhoon Krosa (known as Typhoon Vinta in the Philippines) swept across the north of Luzon Island on Wednesday 30-Thursday 31 October 2013. All of those known to have died are understood to have drowned. Wilson Lizardo (52) of Santa Marcela in Apayao Province drowned when his boat capsized, Jose Manuel (72) of Lasam in Cagayan Province was swept away by flood waters and Manny Balucas (41) of Lagayan in Abra Province was drowned while trying to cross the river Baybayatin. Loridel Baldos (30) of San Juan in Abra Province and Jerry Gatan (25) of Cabagan in Isabela Province are still missing. In addition around 3500 houses have been destroyed across northern Luzon and a further 23 000 damaged. The storm is now moving towards South China and Vietnam.

The path of Typhoon Krosa. Tropical Storm Risk.

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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