Tuesday, 29 August 2017

Typhoon Hato takes at least twenty six lives in South China and Vietnam.

Twenty five people have been confirmed dead and one is still missing after Typhoon Hato made landfall in Guangdong Province, China, on Wednesday 23 August 2017. Ten of the deaths occured on the island of Macau, with nine in Guangdong, one in Guangxi and five in Yunan; an additional death, of an 87-year-old man in Hong Kong, which was initially blamed on the storm, has now been attributed to other causes, though 121 people have been injured there. Around 27 000 people were evacuated from low-lying coastal areas in Guangdong Province, probably helping to minimise the number of casualties there. A single death was recorded in Vietnam, where over 750 houses have reportedly been damaged by the event. Both countries have suffered extensive damage to aggricultural land and severe disruption to transport networks.

Typhoon damage on Macau on 24 August 2017. Anthony Wallace/AFP/Getty Images.

Tyhoon Hato was a Catagory 3 Typhoon when it made landfall, with sustained wings in excess of 185 kilometres per hour recorded in Hong Kong, and a storm surge in excess of a 130 cm hitting parts of the Chinese coast. 

Storm damage in Hong Kong after the passage of Typhoon Hato. South China Morning Post.

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 in rushing 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 in Zhuhai City in Guangdong Province caused by Typhoon Hato. AFP.

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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