A spell of extremely heavy rain that lashed parts of northern Bangladesh and its adjacent upstream hills across the border in India triggered a flash flooding, leaving tens of thousands of people stranded in three upazilas of the bordering district of Sherpur.

The wet spell dumped a massive amount of rain since Thursday over a vast landscape in Bangladesh, and India’s Assam and Arunachal Pradesh, leading the Bhugai River to swell by 21 feet in just 24 hours, sending a huge wave of water towards an area inhabited by largely farmers.

The extent of the damage caused by the flooding could not been known immediately as the onrush of water from the upstream Meghalaya mountain region cut off villages from one another, submerging roads, mostly unmetalled country roads, under waist-deep floodwater in the affected Nalitabari, Jhinaigati and Sribardi upazilas of the district.

‘We cannot reach many affected people for rescue because of lack of boats,’ said Torofdar Mahmudur Rahman, deputy commissioner in Sherpur, adding that three upazilas were affected by the flash flooding.

‘People are either stuck in their houses or moved to roads,’ he said.

There, however, are not many metalled roads for people to take shelter in the three upazilas where road communication is very poor with around 300km of metalled road much of which went under waist-deep water by Friday afternoon.

The three upazilas of Nalitabari, Jhenaigati and Sreebordipur, home to nearly seven lakh people living in an 812 square kilometre of area, began experiencing the flash flood on Friday morning to intensify by afternoon, the district’s relief and rehabilitation office said.

The district administration ordered the making of rafts to rescue the affected people as it was able to arrange merely four rescue boats.

The flood-affected people are mostly farmers, including hundreds from various national minority communities.

The floodwater submerged the Jhenaigati upazila health complex by several feet, seriously hampering health services.

The Bangladesh Metrological Department warned on Friday afternoon that the very heavy rain was likely to continue over northern Bangladesh and its adjacent upstream areas in the next two days, if not more.

A fresh low pressure area also formed on Friday over the west Bay of Bengal, intensifying the fear of bringing more rain onto land.

In the 24 hours until 9:00am Friday, the Flood Forecasting and Warning Centre said that the Nakuagaon point in Sherpur received 261mm of rainfall. Very heavy rain, up to 200mm, was also recorded in adjacent Netrakona, Mymensingh, Jamalpur and Tangail districts over the same period.

Weather stations in some of the affected areas are finding it somewhat difficult to understand the extent of deviation in the rainfall event, particularly given that the monsoon officially withdrew four days ago.

For Mymensingh, the average normal rainfall for the day, according to the meteorological department, was 11.8mm. But the flood forecasting and warning centre said that in the 24-hour reporting period, Mymensingh received 68mm rainfall, nearly a third of the average normal monthly rainfall of 209mm in October.

The upstream areas witnesses even more rainfall. Vast areas in Assam received extremely heavy rain with many areas experiencing nearly 1,000 per cent or far more excessive rainfall for the day ending at 8:30am on Friday.

Morgaon in Assam received 2,894 per cent excessive rainfall, followed by Sonitpur receiving 2,004 per cent excessive rainfall, south Garo hills 1,892 per cent, and southwest Khasi hills 886 per cent. In Arunachal, Subansiri area recorded 1,656 per cent excessive rainfall compared with its normal rainfall for the day.

‘The rain is far more than expected at this time of year. It occurred almost all over Assam and Meghalaya,’ said Sarder Udoy Raihan, executive engineer, FFWC.

The trans-boundary Bhugai River swelled by 640cm over the 24 hours until 9:00am on Friday, said the flood forecasting centre, adding that the river was flowing 200cm above its danger mark at 3:00pm.

In a bulletin issued on Friday afternoon, the centre said that the Bhugai along with Kangsha, Someswari and Jinjiram rivers might keep rising for the next 24 hours.

Some low-lying areas in Sherpur, Netrakona and Mymensingh districts might be inundated over the time.

Centre for Environmental and Geographic Information Services executive director Malik Fida A Khan said that the Bhugai is rather a narrow river and it reached a height that was far more than normal in the gap of a day.

‘Bhugai is a flashy river and swelling by 2 metres in a day is normal,’ he said.

Light to moderate rain accompanied by temporary gusty wind is likely to occur at most places over Rajshahi, Mymensingh and Sylhet divisions, and moderately heavy to very heavy rainfall at places over Rangpur, Dhaka, Khulna, Chattogram and Barishal divisions, the Bangladesh meteorology department said in a bulletin at 6:00pm on Friday.

Bangladesh’s highest rainfall of 211mm in the 24 hours until 6:00pm on Friday was recorded in Tangail, the department said.