100-Year Storms Now Expected at Least Once a Decade in Bangladesh, Study Finds

What once were hundred-year extreme storms in Bangladesh could now strike the country once a decade or more due to climate change, a recent study from MIT shows.

Bangladesh is one of the most densely populated places on Earth, with more than 170 million people living in an area about the size of New York state. Much of the country is made up by the huge, low-lying Ganges Delta, making it especially susceptible to flooding and extreme weather from climate change.

The study found that the “return period,” or the amount of time between these massive storms, is increasing dramatically due to climate change and that these massive storms will become more devastating, with some areas of Bangladesh potentially seeing the tide from these storms rise by more than a meter in height. 

Sai Ravela, one of the study’s authors and principal research scientist for Earth, atmospheric and planetary sciences at MIT, told EcoWatch that this is a first-of-its-kind study for Bangladesh that models future climate scenarios. 

The researchers used complex computer models capable of quickly simulating tens of thousands of simulations to model storm surges, tides, sea level rise and cyclones under different warming scenarios.

“The results are quite stark. No matter where you look, whichever scenario you look at. And by the by the end of the century, if you look at what a 100-year return period looks like in future climate versus present climate, you see an order of magnitude change. 100-year return periods have become 10 years,” Ravela said.

In addition to the low-lying nature of the country, Bangladesh has more than 100 polders, or low-lying land area, which were built about 60 years ago to combat coastal flooding and salinity (saltwater) intrusion into crops. But these polders might not be the best solution.

As climate change worsens, there is also an increasing overlap between the late monsoon season, which occurs between June and October, and the cyclone season. “This has never happened before,” Ravela said. “I mean, you never see cyclones in the monsoon season. Why would you?”

People wade through floodwaters in Feni, southeastern Bangladesh on Aug. 24, 2024. Sultan Mahmud Mukut / Drik / Getty Images

Because the monsoon season is worsening and lengthening, and the ocean continues to warm, the country will see these two seasons increasingly overlap. 

The study also suggests that back-to-back cyclones are becoming increasingly likely. 

“What’s happening is that outside the polder, where the channels and rivers are, there’s silt that’s getting deposited. So the river bed is rising, the land inside the polar is sinking. So when there’s a flooding event, there’s a huge amount of water that’s deposited,” Ravela said. 

He explained that because certain pieces of infrastructure, like pumps and sluice gates, don’t have the proper capacity to operate under these storms, there’s an enormous amount of saltwater deposited, salinating the soils and threatening agriculture as a result.

“And in this comes a cyclone. And what the cyclone does is it generates an enormous amount of strong tide, and the tidal amplification takes that water much further inland because of the way the river bed is, and it deposits a whole bunch of saline water inside these polders… And the economy just upends completely. [You] go from agriculture to no agriculture after just one cyclone. It takes eight years for that salinity to leech.”

Ravela said that one of the uses for the research is to understand which policies would help the country adapt to these storms. The polders, for example, are about four to five meters, which he said is not enough to compare these storms. 

“It’s a controversial point, but do you even need the polders? Are they doing any good? Why wouldn’t we just, for example, remove the poulders and let it flood?” Ravela said. “But along with that flood comes so much sediment that it makes it very appealing to grow for part of the year on it. So there are other sustainable strategies that are born out of nature-based solutions, natural wisdom… I mean it’s unbelievable how much technology we dump without really thinking through it.”

Because the salinity renders cropland unusable, like in southwest Bangladesh, many people turn to shrimp farming, Ravela said. “Everybody tries to be a shrimp farmer. But the problem with shrimp farming is it’s so capital intensive that people who own their land before doing farming — and you need large pieces of land to do shrimp farming — turn to shrimp farming, and they become indentured laborers in their own farms, because these farms are now owned by somebody outside putting in a lot of money, and then that loss of ownership is a part of their story.”

Solving creeping problems like salinization likely requires broader governmental action, like negotiating with India to allow for more freshwater to flow into Bangladesh, he said.

With so many people facing natural disasters and the loss of their land and livelihood, many are fleeing. But as one goes farther north and away from the coast, the threat of salinization diminishes, although the risk of intense storms is still present. In these middle areas, Ravela explained, people are implementing agrivoltaics, aquaculture or even going back to rice farming as the soil in certain areas, like the southwest, is leeching away salt. 

Other ways Bangladesh can prepare for these storms, he said, are by embracing old ways of agriculture. “Eight months out of the year, you grow. Four months out of the year, you let it flood, and it brings a fertile soil and the water recedes, and you can live the rest. You put your house on stilts and you migrate seasonally.  You can slow down the storm tide. For every kilometer, you can drop a meter. And there are other benefits from the perspective of biodiversity and conservation that also that brings in,” Ravela said.

“Insofar as extreme events are concerned [like] the episodic modification of the soil properties, I think we can have a handle on that in this vulnerable mid portion north of Gabura, but South of safe zones like Keshabpur and Jessore.”