Beyond rain: Causes behind recent floods

Highlights:

• The flood was far more severe than expected given the amount of rainfall
• Previous heavy rainfall in the region did not lead to such devastating floods
• Water levels rose to unprecedented heights, exceeding 14 feet in some areas
• Rainfall data predicted much lower water levels than were observed
• The Gumti, Khowai, and Feni rivers experienced record-breaking water levels

Bangladesh, a country frequently affected by seasonal floods, has recently experienced one of its most devastating floods.

While the region did receive significant rainfall, the severity of the flooding was far beyond what would be expected based on the amount of precipitation, raising concerns about underlying factors contributing to the disaster.

Feni, one of the hardest-hit areas by recent floods, recorded 435 millimetres of rainfall between 16 and 22 August, with the maximum in a day being 150 millimetres on 19 August. This significant downpour led to a rapid increase in water levels in the region.

On 16 August, the water level at the Parashuram station of the Muhuri River in Feni was 7.2 metres, rising to 13.42 metres by 21 August—a nearly 20-foot increase in just five days.

However, according to experts, the water level should have only risen by about 1.5 feet based on rainfall ratios.

Historically, Feni experienced a major rainfall event on 2 August 1982, when 280 millimetres of rain fell in a single day. Despite the increase in water levels back then, the region did not face such devastating floods as it did this time.

This discrepancy highlights the unusual nature of the floods, which affected at least 11 districts across the country, with water levels exceeding 14 feet in some areas.

Despite heavy rainfall, the accumulated water level should not have surpassed two feet, according to data from the Bangladesh Meteorological Department (BMD).

Although the Indian states of Tripura and Meghalaya also experienced high rainfall, previous record-breaking rains in these areas did not lead to such severe flooding.

BMD Meteorologist Dr Muhammad Abul Kalam Mallik said, "This rainfall is not a record. We have seen higher rainfall in flood-prone areas in the past, and while this was heavy, it should not have caused such devastating floods."

Abul Kalam pointed out that the floods were not solely due to internal rainfall in Bangladesh.

"Upstream water from India, decreased navigability of rivers, rising tidal waters due to low pressure, and the gradual contraction of reservoirs contributed to the prolonged and widespread nature of the floods," he said.

Further analysis of BMD's rainfall data shows that Cumilla recorded 183 millimetres of rainfall on 19 August and 188 millimetres on 20 August, totalling 557 millimetres between 19 and 22 August.

Despite this, the water level should have only increased by a maximum of 22 inches.

Similarly, Chattogram saw 113 millimetres of rainfall on 20 August and 567 millimetres over the week, with a predicted maximum water level rise of 22 inches.

Cox's Bazar recorded 140 millimetres of rainfall on 17 August, contributing to 715 millimetres over the week, which should have led to a water level increase of 28 inches.

During the floods, on 21 August, 300 millimetres of rainfall were recorded in Sonamura and 143 millimetres in Bilonia, Tripura.

According to the Flood Forecasting and Warning Centre (FFWC), water levels in the Gumti River in Cumilla, the Khowai River in Habiganj, and the Ramgarh station of the Feni River have broken 60-year records.

Additionally, water levels in the Indian sections of the Ramgarh and Pashuram rivers in Feni district also approached record levels.

FFWC Executive Engineer Sarder Udoy Raihan said, "This is the first time Bangladesh has faced floods at so many points simultaneously. Moreover, the floodwaters are receding much more slowly than usual. Typically, floodwaters recede within 2-3 days, but this time, some areas have not seen water recede even after a week."

He underscored the fact that upstream flooding from India played a major role in worsening the flood situation.

"None of the rivers shared with India have dams on our side, so our water levels depend on upstream water from India. However, India never shares information about dam operations with us, only providing regular river water level and rainfall data for a few points," he said.

Raihan said that last year, India informed Bangladesh when the Teesta dam in Sikkim broke, allowing time for warning and preparation. However, this time, no such information was shared. 

Rivers from Tripura that enter Bangladesh often have dams on the Indian side, and experts believe that if the water flow had been natural instead of being artificially blocked, the flooding would not have been as severe.

During a recent joint river commission meeting between Bangladesh and India, Bangladesh requested three types of information from India to improve flood forecasting: upstream rainfall and water flow rates, three-day rainfall forecasts, and details on when India's 60 upstream dams would be opened and the expected downstream water flow.

Despite multiple requests, India has not provided this information, only sharing data on water level increases at 14 points of common rivers, related sources said.

Mohammad Azaz, chairman of the River and Delta Research Centre, criticised the Joint Rivers Commission as largely ineffective.

"Bangladesh receives data from only 8 out of 54 stations on the Bangladesh-India border, without any information on dam operations. This commission has not benefited Bangladesh in the last 15 years," he said.

Azaz urged the government to make the commission effective and called for Bangladeshi officials to be stationed at dams on rivers flowing into Bangladesh to share regular updates.

He also cited a study by the RDRC indicating that there are at least 60 dams in India on the Bangladesh border, none of which generate more than 300 megawatts of electricity.

"These dams are used as weapons by India, exacerbating the severity of floods in Bangladesh," Azaz added.

He also pointed out that the previous government contributed to the flooding by filling up rivers and reservoirs and destroying natural barriers, exacerbating the impact of climate change.