Monday 30 October 2017

Family forced to evacuate home after landslide in Pahang State, Malaysia.

A family of five has been forced to evacuate their home after a landslide in the town of Mentakab in the Temerloh District of Pahang State in Peninsula Malaysia on Sunday 29 October 2017. The incident happened at about 4.00 pm local time, on the road downslope of the property, but has apparently partially undermined the building. The family has been ordered to leave by local authorities in case of further land slippage.

Property in Temerloh District, Pahang, partially undermined by a landslip on 29 October 2017. Pahang Civil Defence Force.

he cause of the event is as yet unclear, but Peninsula Malaysia has been suffering an exceptionally wet rainy season, with numerous floods and related occurrences. 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. Malaysia has become increasingly landslip-prone in recent years due to extensive deforestation, which leaves soil exposed to heavy tropical rainfall. Concerns have also been raised about the large number of construction sites on steep hillslopes in urban areas, where workers are particularly vulnerable to landslip events during the rainy season.

Pahang has a wet tropical climate with rain averaging over 200 mm per month, but has distinct wetter and dryer periods within this. October and November are typically the months with the highest rainfall,  usually over 390 mm in each month, associated with monsoon winds from the South China Sea.

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.

Southeast Asia has two distinct Monsoon Seasons, with a Northeast Monsoon driven by winds from  the South China Sea during the Southern Hemisphere Summer and a Southwest Monsoon driven by winds from the southern Indian Ocean in the Northern Hemisphere Summer. Such a double Monsoon Season is common close to the equator, where the Sun is highest overhead around the equinoxes and lowest on the horizons around the solstices, making the solstices the coolest part of the year and the equinoxes the hottest.

The winds that drive the Northeast and Southwest Monsoons in Southeast Asia. Mynewshub.

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