Monday 18 November 2013

Death toll from Typhoon Haiyan nears 4000.

The number of people known to have died after Typhoon Haiyan (known in the Philippines as Typhoon Yolanda) hit the Eastern Visayas islands in the central Philippines on Friday 8 November 2013 is likely to reach 4000 today (18 November), with the World Health Organization warning that the numbers dying is likely to rise further due to infected wounds not receiving adequate treatment and people being unable to gain medication for pre-existing medical conditions, such as diabetes or heart disease. The organization has further warned that conditions on the worst affected islands, Samar and Leyte, are a perfect environment for the spread of water-borne diseases such as cholera or typhoid.

Damage in Tacloban, the capitol of Leyte Island, following Typhoon Haiyan. World Vision Australia.

Typhoon Haiyan first hit the island of Kayangel in the Republic of Palau on Wednesday 6 November, where it is reported to have destroyed every home on the island, but miraculously not taken any lives. Two days later the Typhoon hit Samar Island in the Philippines bringing with it sustained winds of 315 km per hour (i.e. periods in which the wind speed stayed at or above 315 km per hour for over a minute), making it the most powerful tropical cyclone ever recorded making landfall and the fourth most powerful ever recorded. 

Survivors in Tacloban on 10 November 2013. Erik de Castro/Reuters/Trust/Care.

In addition to high winds Typhoon Haiyan brought widespread flooding, with 281.9 mm of rain recorded in Surigao City on Mindanao Island and a 5.2 m storm surge hitting Tacloban. 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.

A ship lifted onto land by the storm surge that hit Tacloban. Stern.

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.

Storm damage on southeast Panay Island in the Western Visayas (also Philippines). Reuters.

Typhoon Hainan is already considered to be the second most destructive storm ever to hit the Philippines (after Tropical Storm Thelma which killed over 8000 people in 1991), with some agencies predicting the death toll could eventually exceed 10 000. The International Red Cross is currently estimating 22 000 people are missing following the storm, though missing figures typically shrink significantly as infrastructure is restored following disaster events, and cannot be used as an accurate proxy for eventual casualties.

Bodies being placed in a mass grave at Basper Cemetery in Tacloban. Aaron Favila/AP.

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