How climate change is behind frequent northeastern floods

The rapidly deteriorating floods coupled with heavy downpour, which kept the northeastern region isolated from the rest of the country and hundreds of thousands of people stranded for nearly a week, are heading towards being the most devastating in recent memory.

Climate change is identified as a key reason, among others, behind the frequent floods in the Sylhet division and adjoining Indian states in recent years.

A warmer climate influenced the weather patterns and variability in the middle of the Himalayan regions and increased rainfall and precipitation that have contributed to the current floods in Sylhet, according to Anjal Prakash, coordinating lead author of the United Nations' Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate.

"Studies have shown that the changing Himalayan region's rainfall patterns are leading to unpredictable weather," said Prakash, who is also research director of the Indian School of Business.

"As extreme weather events have been seen across South Asia over the last decade, it can be said there is a strong connection between climate change and early monsoon and excessive flash floods," according to AKM Saiful Islam, professor of flood management at the Bangladesh University of Engineering and Technology (BUET).

At least 12 northeastern and northern districts – including four of Sylhet – in Bangladesh are currently reeling from the devastating floods, with major rivers such as the Brahmaputra, Jamuna, Surma, and the Kushiyara flowing above the danger mark at 18 points. The old Surma River has already broken its historical water level record at Derai, flowing at 7.55m, surpassing the previous water level record of 7.29m, according to the Flood Forecasting and Warning Centre in Bangladesh.

On 17 June, Cherrapunji in Meghalaya received 972 mm of precipitation, just two days after recording 811.6 mm of rainfall in a day, Indian media reported, citing the India Meteorological Department. Ever since the department began keeping records, more than 800 mm of rain on a June day was recorded nine times, four of them since June 1995.

In Bangladesh, Lourergorh in Sunamganj and Lalakhal in Sylhet received more rain than the average normal for this month. Lourergorh received 1648 mm of rain against the average normal of 1495 mm, while Lalakhal received 2129 mm of rain against the longtime average of 2059 mm, according to the Flood Forecasting and Warning Centre. Other rivers are flowing very close to their historic water levels. It is feared they will set new water level records soon.

"The strong monsoon winds in the Bay of Bengal can carry a lot more moisture than ever, in response to global warming. A response to rising temperatures is the overall increase in moisture levels in the atmosphere. This is because warmer air holds more moisture, and that too for a longer time. Hence, the large amount of rainfall that we see now might be a climate change impact," according to Roxy Mathew Koll, lead author of IPCC Oceans and Cryosphere.

IPCC reports also show that the variability of rainfall is a problem as it creates skewed rainfall patterns, deviating from the known characteristics of the South Asian monsoon. It spreads out rain throughout the season, which accounts for most of the year's rain. 

"There's been a climatic shift in monsoon patterns over South Asia since the 1950s," he said and added that for every 1-degree Celsius rise in temperatures, the total amount of rainfall increases by 7%, up to 10% in the monsoonal region.

Roxy Mathew projected that extreme rainfall events will increase proportionally over South Asia in the coming years.

The changing nature of flooding 

"The nature of flooding has also changed over the years. Earlier this year, we witnessed early flooding before the monsoon. Now we are hit by another catastrophic flooding," Professor Saiful Islam said. "The situation was not like this a few decades ago." 

The professor called for preparing for unpredictable flooding in the future. 

"Excessive rainfalls are seen every 10-12 years. But, the frequency of natural disasters has been on the rise over these past few years and will continue in the future," said Ainun Nishat, professor at the Centre for Climate Change and Environmental Research of BRAC University.  

"We already see frequent excessive and untimely rainfalls. Previously, we witnessed cyclones and storms."  

In the coming 10-15 years, it is feared that more natural disasters will hit climate-vulnerable countries such as Bangladesh, he said. ***