Friday 26 May 2017

Flooding and mudslides kill at least 91 in Sri Lanka.

At least 91 people have died and over 110 are missing after heavy rain triggered flooding and mudslides across central, western and southern parts of the country on Thursday 25 and Friday 26 May 2017. The worst incident occured in Bulathsinhala District in Western Province, where at least eleven people are known to have died in a single mudslide, while 38 people are reported to have died in flooding in Kalutara District in Central Province and 46 in Ratnapura District in Southern Province. 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.

The  aftermath of a landslide in the village of Bellana in Kalutara District, Sri Lanka, on 26 May 2017. Eranga Jayawardina/AP.
Eranga Jayawardena
Eranga Jayawardena
Eranga Jayawardena
Eranga Jayawardena
Eranga Jayawardena

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/2017/04/twenty-six-confirmed-dead-and-over.htmlhttp://sciencythoughts.blogspot.co.uk/2016/05/flooding-and-landslides-kill-at-least.html
http://sciencythoughts.blogspot.co.uk/2014/12/at-least-six-dead-following-landslide.html
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