Fifteen dead in flooding in southern Thailand.

Fifteen people have died in flooding in southern Thailand since 25 November 2017, ten of them in the last week. Several hundred thousand people are thought to have been affected by the flooding, which has been caused by a particularly wet monsoon season, but is widely thought to have been made worse by a volatile political situation, which has hampered the country's ability to plan for such events.

Floodwaters in Phatthalung Province, Thailand, in November 2017. DDPM.

Thailand has a tropical climate, with a monsoon season that usually lasts from June to October. Typically September produces the highest rainfall, with the rains trailing off in October. However, as with other countries in Southeast Asia this year, the rains have been exceptionally heavy and prolonged this year, so that reservoirs and barrages have filled to capacity by the beginning of October, and the rains have persisted longer, pushing water storage systems beyond their capacity.

Flooding in Narathiwat Province, Thailand. AFP.

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. This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea. 

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

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