Sunday, 2 August 2015

Death toll thought to have exceeded 120 as Cyclone Komen makes landfall in Bangladesh.

Over 120 people are feared to have died after Cyclone Komen made landfall in Bangladesh on 1 August 2015. The storm brought widespread flooding to coastal areas of northern Myanmar, Bangladesh and West Bengal, Odisha and Manipur States in India. In Myanmar flooding has displaced around 150 000 people and destroyed over 17 000 homes, with at least 27 known to have died. In southern Bangladesh 23 people are known to have died and more than 130 300 to have been displaced, with over a meter of rain being recorded within 24 hours in parts of Chittagong. In India the state of Manipur has suffered the worst flooding in thirty years, with around 100 000 people having been displaced from their homes, with parts of the state cut off by flooding and 20 people reported to have died in a single landslide event; landslides 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. In Odisha State at least 500 000 people have been forced to flee their homes due to flooding and at least three people have died. In West Bengal over 200 000 people have been displaced and 180 000 homes damaged or destroyed, with much of the city of Kolkata under water, after several hydro-electric dams were forced to release water to avoid catastrophic overload. At least 48 people have died in the West Bengal.

Damage to a bridge caused by high floodwaters in Chandel District, Manipur. NDTV.

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.

Flooding on the streets of Kolkata on 2 August 2015. The Economic Times.

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.

See also...

Six people are known to have died and 350 000 people have been evacuated from coastal areas after Cyclone Huhud hit the city of Visakhapatnam on the coast of...

Twenty three people are now known to have died after Cyclone Phailin made landfall in Orissa State, India, slightly after 9.00 pm local time on Saturday 12 October 2013, brining with it winds of up to 220 km per hour...

Ten people are known to have died and several more are missing after Cyclone Helen made landfall in Andhra Pradesh State, India, at about 1.30 pm local time (8.00 am GMT) on Friday 22...

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