Sunday, 22 May 2016

Flooding and landslides kill at least seventy three in Sri Lanka.

Seventy three people have been confirmed dead and hundreds more are still missing after the heaviest rains in over twenty years have brought widespread flooding and numerous landslides. The worst hit area is in the Kegalle District in the central part of the country, where a series of huge landslides have engulfed at least three villages, and driven back repeated rescue missions by the Sri Lankan military. Landslides 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. Other areas of the country, including the capital, Colombo, have suffered extensive flooding, with close to a quater of a million people in temporary shelters.

The aftermath of a landslide in Kegalle District, Sri Lanka, on Wednesday 18 May 2016. Eranga Jayawardina/AP.

The rains are associated with the onset of the Sri Lankan summer monsoon, which lasts from May to October, typically brining around 400 mm of rain to many parts of the country in an average year. Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate. 

 Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

See also...

http://sciencythoughts.blogspot.co.uk/2015/12/heavy-rains-bring-further-flooding-to.htmlHeavy rains bring further flooding to Chennai, Tamil Nadu.                                                 Heavy rains have brought further flooding to the city of Chennai in Tamil Nadu, India, with about 8 cm of rain falling on the morning of Tuesday 1 December...
http://sciencythoughts.blogspot.co.uk/2014/12/at-least-six-dead-following-landslide.htmlAt least six dead following landslide in Badulla District, Sri Lanka.                             At least six people are known to have died following a landslide at Rilpola in the Badulla District of Uva...
http://sciencythoughts.blogspot.co.uk/2013/08/a-least-five-dead-following-landslide.html 
At least five dead following landslide in Kerala State, India.                                      Five people are known to have died and another fifteen, including two foreign tourists, are believed to still be buried in their vehicles following a...


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