The worst floods in Bangladesh in more than a century have killed dozens of people so far and displaced nearly 4 million people, with authorities warning the water levels would remain dangerously high in the north this week.
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Bangladesh, a densely populated delta nation, is also one of the world’s most climate-vulnerable where the poor are disproportionately impacted as frequent floods threaten livelihoods, agriculture, infrastructure and clean water supply.
A 2015 study by the World Bank Institute said about 3.5 million of Bangladesh’s 160 million people are at risk of river flooding every year.
Saiful Islam, director of the Institute of Water and Flood Management (IWFM) at the Bangladesh University of Engineering and Technology (BUET), analysed 35 years of flooding data and found that rains were getting more unpredictable and many rivers are rising above dangerous levels more frequently than before.
“The last seven years alone brought five major floods, eroding people’s capacity to adapt, especially in the country’s northern and northeastern regions,” Islam told Al Jazeera.
Citing one of his research papers, he said even if average global temperatures increase modestly – by 2 degrees Celsius (3.6 Fahrenheit) over the average for pre-industrial times – flooding along the Brahmaputra river basin in northeastern India and Bangladesh is projected to increase by 24 percent.
With an increase of 4 Celsius (7.2 F), flooding is projected to increase by more than 60 percent, Islam’s research indicated.
Several rivers, including the Brahmaputra, one of Asia’s largest, flow downstream from India’s northeast through the low-lying wetlands of Bangladesh as they drain into the Bay of Bengal.
However, this year, the excess rainwater from India’s Assam and Meghalaya states that flows into Bangladesh’s Meghna and Jamuna Rivers could not drain because the wetlands were already saturated by an earlier pre-monsoon flood last month.
“The siltation of riverbeds caused by deforestation and solid waste dumping has already reduced the water carrying capacity of the rivers in Bangladesh,” Ashiq Iqbal, a researcher at IWFM, told Al Jazeera.
“Besides, excessive sand and stone mining in upstream India has loosened the soil, which ultimately ends up into river bottom and decreases the navigability. As a result, the whole systems get clogged. And this clogged system has lost its ability to drain out water from two quick successive floods in short time,” he said.
Unplanned construction along the northeastern wetland is another reason rivers have become clogged arteries, Mominul Haque Sarkar, senior adviser at the Centre for Environment and Geographic Information Services (CEGIS), told Al Jazeera.
“A lot of pocket roads as well as culverts are being constructed in different places across the wetland. As a result, water flow gets obstructed and it gets swelled when it rains excessively,” Sarkar said.
Most of the towns and villages in northern Bangladesh do not have protection dams. So when the water level in the wetlands or rivers starts rising, it quickly enters the residential areas and inundates them, he said.
To cope with the floods, conventional methods such as building embankments along major rivers were proposed as part of a Flood Action Plan implemented in 1990.
But some experts say structural measures to contain floods are ineffective.
Mohamad Khalequzzaman, geoscientist at Lock Haven University in the United States, told Al Jazeera it is “difficult and undesirable to contain flood with fortified walls”.
“It may be necessary to contain floods in selected places where a high concentration of population and resources are located, such as in big cities,” he said. “But in a geography dominated with wetlands, it is not needed.”
Khalequzzaman said walling off low-lying areas using permanent embankments, or polders, has been a popular intervention in countries such as Bangladesh. “Polders separate rivers from floodplain which in turn intensifies flow in the river and causes riverbank erosion,” he said.
He said water resources in Bangladesh’s major rivers should be managed involving all co-riparian countries in the Ganges-Brahmaputra-Meghna (GBM) basins – Bangladesh, India and Bhutan.
“The problem is only 8 percent of the GBM basins are located within the geographic territory of Bangladesh. So, in reality, without an integrated water resources pact among all countries in the GBM basins, floods cannot be managed properly in Bangladesh,” he said.