This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In the humid tropics of Southeast Asia, afternoon thunderstorms roll through almost every day. Daytime heat causes towering, fluffy cumulonimbus clouds to form and swell before unleashing torrential rain on cities such as Singapore, Hong Kong and Bangkok.
In these places, drainage systems are designed to cope with short, heavy downpours. But the rains in Bangkok over the last week were far from typical. September is the wettest month in Thailand's bustling capital, with a monthly average of 344 millimeters (13.5 inches) usually spread across 18 rainy days.
But just last week, roughly 300 mm (11.8 inches) of rain fell in Bangkok over 48 hours, overwhelming the city's drainage systems. This extraordinary volume of water prompted authorities to declare a citywide disaster zone. As stagnant, brown water has inundated the city, at least 31 people have died and thousands have been forced to evacuate.
This sudden and extreme downpour was caused by a low-pressure system that stayed over the Bangkok region for about three days. In a low-pressure system, air rises and moisture in the air condenses to form clouds and rain. If a low-pressure system stalls, it can dump rain over the same location for days, leading to severe flooding.
In the nearby Gulf of Thailand, sea surface temperatures are sitting close to 30°C (86°F), several degrees above the local average. These warm conditions provide ample moisture and energy for the storm to persist. Thailand is no stranger to flooding.
In 2011, more than 800 people died when high rainfall, multiple tropical storms, high sea levels and an early start to the monsoon season collided. This triggered widespread flooding that lasted months. World Bank figures show these floods caused an estimated US$46.5 billion in damage, with the local manufacturing industry hardest hit.
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