Floods: Cloudbursts from Tripura to Feni

Cold air from the west entered the sky of the country’s eastern regions while a low pressure area in the Bay of Bengal arrived near Cumilla and Noakhali via Cox’s Bazar and Chattogram, and, in the meantime, the monsoon was bolstered. Together these three factors led to the accumulation of layers of clouds in the skies of Cumilla and Noakhali, and those eventually burst into rain, what the experts call ‘cloudbursts.’

Cloudbursts began on the morning of 19 August. After that, incessant rainfall and water from upstream submerged the eastern region of the country. Cloudbursts expanded over 50 to 70 kilometres from Tripura in India to Cumilla and Feni in Bangladesh. These regions saw heavy rainfall on 19, 20 and 21 August.

Meteorologists said this after analysing the causes of flash foods. Such cloudbursts occurred from South Asia to China to Australia after a gap of several years. Water from heavy rainfalls was not receding due to rivers, canals and other water bodies being filled with soil.

Bazlur Rashid, a meteorologist at the Bangladesh Metrological Department (BMD), has been researching climate change in Bangladesh for over 15 years. According to his research data, Bangladesh saw cloudbursts in the Rangpur region in July 2020. About 447 millilitres of rainfalls were recorded in those areas between the night of 26 September and the morning of 27 September that year – the highest in the past 70 years.

Cloudbursts also hit Sylhet on 18 June 2022 as 304 millimetres of rainfall inundated the entire city and haor areas in just a day. The previous day, 1,004 millimetres of rainfall occurred in Meghalaya of India, upstream of Sylhet. Heavy rainfalls and water from upstream submerged 80 per cent of the area in Sylhet and Sumanganj. Heavy rainfall is not usually in these rain-prone areas where 200-300 milometers of rainfall occur during the rainy season.

As many as 435 millimetres of rainfall occurred in Feni between 19 August to 22 August while more than 557 millimetres in Cumila and 605 millimetres of rainfall in Noakhali were recorded during this period.

Meteorologist Bazlur Rashid said the low pressure area in the Bay started crossing over Bangladesh territory on 16 August and it turned into a well marked low and arrived with huge clouds. On the other hand, the west wind brought cold air at the same time. Warm clouds from the sea mixed with cold air forming huge clouds in the sky of the country. Cloudbursts occurred after those clouds sustained for a long time over Feni, Noakhali and India’s Tripura due to surface pressure, resulting in heavy rainfalls in a short duration of two to three days.

According to BMD’s observation, Cumilla, Noakhali and Chttogram saw more than 300 millimetres of rainfalls in 24 hours at least 22 times between 1958 and 2024. Until this week, rainfall did not cross 300 millimetres that much in any district. Yet, flood situations worsened.

Meteorologists explained that it also needs to look into the time frame before this cloudburst. Rain occurred intermittently in those areas throughout the past month. About 200 millimetres of rainfall occurred in Feni and Noakhali at the end of July and mid-August, causing the river water to flow over danger marks. Rainfall did not last for over a day in the past. So, there was enough time for water to recede. As a result, no severe floods happened.

River and water experts say that there is a basic difference between the Teesta and Ganges basins with the Muhuri and Gumti basins. The heavy rains over Teesta and Ganges take place 400 to 600km away from Bangladesh's border. And the width of these rivers is one to two kilometres. So it takes from there to seven days for the water there to flood Bangladesh's coastal areas.

But Feni and Cumilla are 100 to 150km away from Tripura and the rivers here are 200 to 300 metres. So water rushes in rapidly and has flooded these areas.

As there as no forecast of cloudbursts and as the force of the water was strong, the damages have been worse, say concerned persons.