What’s causing sudden floods in Bangladesh?

Eight districts in Bangladesh are experiencing severe flooding caused by heavy rainfall and upstream water releases.

Meteorologist Mostofa Kamal Palash, a PhD researcher in meteorology and climate at the University of Saskatchewan, identified three primary factors contributing to the ongoing floods in Bangladesh.

First, a persistent monsoon low-pressure system over Bangladesh has caused continuous rainfall. As of Wednesday afternoon, this system was stationary over the Chattogram region and was expected to bring rain across much of the country until Thursday night.

Second, a strong Madden-Julian Oscillation, a significant component of tropical atmospheric variability, is currently active over the Bay of Bengal, causing warm, moist air to move towards the coast.

Third, the jet stream's current position over Central Asia is causing increased rainfall in both India and Bangladesh. 

Forth, India opening the dam is one of the factors behind the flood. India faced flooding with water levels in rivers reaching danger levels due to heavy rain. Every year when India faced flooding they opened the dam. This year also they opened the dam, but in some places the dam gates were damaged as well due to excessive water.

Palash explained that when these three factors align, as they did in June 2017, the region experiences significant rainfall, leading to landslides and floods.

In 2017, this combination resulted in severe flooding in Chattogram, where landslides claimed hundreds of lives.

For the current situation, Palash warned of the possibility of 100-300 millimetres of rainfall in various districts by Thursday midnight, with a gradual decrease expected from Friday onwards.

Bangladesh Meteorological Department (BMD) Meteorologist Md Bazlur Rashid attributed the recent flooding to a low-pressure system that formed in the southern part of the country two days ago. 

"The low pressure caused unusually heavy rainfall in Sylhet and Chattogram, while rainfall in other areas was relatively lower due to warm, monsoon air," he added.

Meanwhile, weather experts warn of a further worsening flood situation, potentially affecting more districts and rivers.