Five people, including three children, have died, three more have been injured and several more are missing after Tropical Depression Basyang (or Sanba) swept across the Philippines on Tuesday 13 February 2018, triggering a series of landslip and flooding events. All of the known deaths have been linked to landslips that hit two villages in Surigao del Sur Province on Mindanao Island. In the first event Irene Lamela Benguilo, 25, and her two children died in a landslide that hit the village of Gamuton, in the second Jay Conjurado, 10, and another, as yet unnamed person, died in a landslide that hit the village of Babuyan.
Rescue workers in Gamuton, Surigao del Sur Province, the Philippines, following a landslide on 13 February 2018. Roselyn Coronel/PTV.
Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Atlantic being referred to as hurricanes.
The path and strength of Tropocal Depression Basyang. Thick line indicates the past path of the storm (till 6.00 pm GMT on Tuesday 13 February 2018), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at six and twelve hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.
Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.
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