Cyclone, storm tides risk increasing

For Abdul Gafur, 56, a resident of Bangladesh’s southern coast, facing tropical cyclones and storm-tides has been a part of life for as long as he can remember. But even with decades of experience, he says he has never seen tidal waves and coastal flooding destroy homes and farmland as they do now.

Gafur lives in Jaliapara village, located in Matarbari Union of Maheshkhali Upazila in Cox’s Bazar. He works as a fisherman. The village, home to at least 2,000 residents, lies to the east of the Kohelia River and borders the Bay of Bengal.

Erosion has plagued the area for several years. In the past five years alone, at least 100 families in Jaliapara have lost their homes to river and coastal erosion. During the monsoon, tidal surges often sweep away houses. Many of those displaced have been forced to move to rented homes in neighbouring areas. Abdul Gafur himself now lives in a rented house after losing his own to erosion.

One of those affected is Nur Hossain, also a fisherman from the village. He told Prothom Alo that although his family has lived in Jaliapara for generations, the tidal flooding they face now is unprecedented. “Our homes never used to flood during the monsoon,” he said. “But over the last five or six years, tidal waves have become more frequent and destructive. One particularly strong wave destroyed our house. Since then, we’ve been living in a rented place.”

Jaliapara falls under Ward No. 9 of Matarbari Union. Local Union Parishad member Mohammad Ali warned that unless a protective embankment is constructed soon, hundreds more families may be displaced in the near future.

While cyclones and tidal surges have long been part of life for coastal communities in Bangladesh, recent years have brought more intense and frequent disasters.

People like Abdul Gafur and Noor Hossain, and countless others along the country’s 710-kilometre coastline, now face a more unpredictable and hostile natural environment - one that threatens not just homes, but their way of life.

Scientists, experts, and environmentalists say the intensifying threat of tidal waves and cyclones in Bangladesh is directly linked to global warming and climate change.

A recent study by researchers from the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology (MIT) in the United States has raised new alarm about the country’s climate future.

The researchers warn that the risk of major cyclones in Bangladesh is increasing significantly. Events that were once expected to occur once in a hundred years may now happen every 10 years. This heightened risk is not uniform—it may vary by region and season.

The threat does not end there. The study found that storm-tide risks associated with these cyclones are also on the rise. During future cyclonic events, the coastal areas of Bangladesh could face tidal surges up to ten times more powerful than those in the past.

Scientists are also concerned about a shift in the seasonal pattern of storms. In the future, Bangladesh may experience more frequent tropical storms and tidal surges during the pre-monsoon and post-monsoon periods - times that traditionally saw fewer such events. This shift could flood new areas and damage agricultural lands prematurely, posing a serious threat to the livelihoods of coastal communities and the country’s food security.

This grim projection for one of the world’s most climate-vulnerable nations was published on 11 April this year in the US-based scientific journal One Earth.

AKM Saiful Islam, professor at the Institute of Water and Flood Management at the Bangladesh University of Engineering and Technology (BUET) and a member of the United Nations Intergovernmental Panel on Climate Change (IPCC), told Prothom Alo, “The findings of this new study give us a fresh direction. These results will significantly inform our climate adaptation strategies. The study clearly suggests that we need to revise our plans to cope with the evolving impacts of climate change.”

It is now widely acknowledged that Bangladesh is among the most climate-vulnerable countries in the world. The country’s geographical features - being a low-lying delta with a funnel-shaped coastline - make it especially prone to natural disasters. Rising sea levels, intense cyclones, and erratic seasonal rainfall continue to expose the deepening impacts of climate change on the nation.

The researchers behind the new study emphasise that Bangladesh is one of the most disaster-prone yet data-poor regions globally. Scientifically, it offers a critical case study for understanding the behaviour of complex and sequential disasters in a changing climate.

Sai Czander Ravela, one of the lead researchers and Chief Scientific Officer at MIT’s Department of Earth, Atmospheric and Planetary Sciences, explained the urgency in an email to Prothom Alo. “The level of risk that Bangladesh faces demands the highest quality modeling, the best scientific research, and urgent cooperation,” he wrote. “The issues we raise here will be relevant not only for Bangladesh, but also for Vietnam, South China, Indonesia, and other deltaic and coastal regions facing similar threats.”

Ravela also expressed a personal connection to the region. “Although I am a citizen of the United States and work there, I am a child of India and I have deep roots in the Bay of Bengal region. This region is significant to me, both scientifically and personally. I feel immense joy and strength in being able to contribute to research that serves Bangladesh.”

The study’s warning is clear: past experiences are no longer reliable guides for future risks. “The most important message is that we cannot rely solely on historical data to understand what lies ahead,” the researchers wrote. “The climate is already changing, and the frequency of extreme events is increasing. Our findings show that cyclones and storm tides once considered ‘once-in-a-century’ events may become decadal—occurring every ten years or even more frequently by the end of this century.”

The study employed an integrated approach using hydrodynamic modeling and advanced statistical analysis to assess future cyclone and tidal wave risks in Bangladesh. The researchers focused on three main areas: synthetic cyclone analysis, hydrodynamic simulation of storm surges, and statistical interpretation of the data.

To begin, the study used a set of artificially generated cyclone tracks to simulate future scenarios under the influence of climate change. These artificial cyclones were designed to assess changes in cyclone intensity and behavior, as well as the impact of sea level rise on storm surges along Bangladesh’s coastline.

At the heart of the cyclone simulation is the Emanuel Model—also known as the Synthetic Tropical Cyclone Generation Model. Developed by renowned climate scientist Kerry Emanuel, one of the co-authors of this study, the model is widely recognised for its ability to generate synthetic storms based on historical data and future climate projections. For this research, the model was applied to analyse cyclonic activity in the coastal regions of Bangladesh from 1760 to 2020.

The artificially generated cyclone scenarios were then fed into a validated hydrodynamic model to simulate storm-tides. This model incorporates high-resolution regional bathymetry to accurately simulate tidal effects and sea level rise. The combined methodology provided a comprehensive picture of how climate change could intensify the risk of storm tides and coastal flooding in the coming decades.

The study assessed the risk of storm-tides in Bangladesh at three levels—national, regional (specifically the Ganges Basin, Meghna Basin, and Chattogram region), and local.

These assessments were conducted under three climate scenarios: normal, moderate, and severe, based on different levels of greenhouse gas emissions and their projected impacts.

To guide these projections, the researchers used the IPCC’s Shared Socioeconomic Pathways (SSPs), a widely accepted model published in 2021. The SSP framework outlines how global society and the economy may evolve under various climate change scenarios through to the year 2100. Using this model, the study examined how storm-tides heights could change over time due to rising sea levels and increasing storm intensity.

According to the study, even under the lowest-impact scenario, the height of storm tides during cyclones in Bangladesh could increase to 4.9 meters by the end of the century.

Under the moderate scenario, this could rise to 5 meters, and in the most severe case, storm tides could reach 5.4 meters. For comparison, the average height of storm tides during past cyclones over the last century has been around 3.5 meters. This means that even in the best-case scenario, tidal heights could rise by at least 1.5 meters by 2100.

If sea level rise is excluded from the projections and only storm intensification is considered, storm tides would still rise by 0.6 to 0.9 meters, depending on the level of change.

Regional analysis reveals that the impact of storm surges will vary significantly by location. The northern part of Chattogram’s coastal district is identified as the most vulnerable, followed by the Meghna region and the Ganges region. The southern part of Chattogram ranks fourth in terms of risk exposure.

The study paints a stark picture of how much more frequent and destructive cyclones and tidal waves could become if the current pace of climate change continues.

Researchers analysed the nature and frequency of past devastating cyclones - such as the 1970 Bhola cyclone and the 1991 Gorky cyclone - to help communicate the growing risk to the public and aid in the development of effective adaptation strategies.

Using multiple model-based analyses, observational data from various stations across Bangladesh, and projections of future climate scenarios, the study found that the average return time of cyclone-induced storm-tides could decrease tenfold by the end of this century if carbon emissions continue at medium to high levels. In other words, storm-tides that were once expected once in a century could now occur every 10 years or even more frequently.

Currently, the most dangerous tidal waves in Bangladesh typically occur during the pre-monsoon (March to May) and post-monsoon (October to November) seasons.

However, the study warns that this pattern is likely to change. Due to the effects of climate change, the interval between severe cyclonic events may shrink dramatically - from the current 75 days to just 15 days.

According to the research, these powerful storms are now spreading across a longer part of the calendar year and becoming more intense. The monsoon period, particularly between mid-August and September, and the post-monsoon window around early and mid-December, are projected to witness the highest increases in cyclone strength and frequency.

During the monsoon season, water levels in rivers and coastal areas are already high. If these are coupled with intense rainfall, either from the monsoon itself or an accompanying cyclone, the risk of simultaneous inland and coastal flooding becomes far greater. This compound threat poses serious challenges for coastal communities and the country’s broader disaster preparedness strategies.

Sai Ravela, one of the study’s lead researchers, emphasised the urgent need for Bangladesh to adopt a forward-looking mindset.

Speaking to Prothom Alo, he said, “Bangladesh needs to prepare for new extreme situations rather than simply reacting after a disaster. We must move beyond a conventional mindset and proactively plan for future risks.”

After the monsoon season ends, a sense of dread sets in for the people of Datinakhali village in Shyamnagar upazila of Satkhira. They live in constant fear of the next storm. “Storms used to come, yes, but there were hardly any tidal waves before,” said Abdul Alim, 50, a resident of the village. “Now, every time a storm hits, it brings a tidal wave with it.”

In nearby Burigoalini village, Hafizur Rahman, a 70-year-old fisherman, and Fatema Khatun, another resident, echoed the same concern. They said that whenever tidal waves hit, saltwater from nearby rivers floods their ponds and reservoirs - polluting their only sources of drinking water. Salinity levels in the land rise sharply, making farming difficult. People are increasingly being forced to purchase drinking water, which was never necessary in the past.

The year 2023 saw three cyclones strike Bangladesh - Mocha, Hamoon, and Midhili. According to climate experts, this frequency is unusual and alarming.

While the total number of depressions and cyclones forming in the Bay of Bengal has declined, the intensity of those that do form is growing. Meteorologists and climate scientists attribute this to the warming of global ocean temperatures - including the Bay of Bengal - leading to more powerful storms.

An analysis of cyclone trends over 75 years (1948–2023) reveals significant changes. Between 1948 and 1962, 20 cyclones formed in the Bay. The highest number - 52 cyclones - occurred between 1963 and 1977.

From 1978 to 1992, the number fell to 30. Between 1993 and 2007, there were 22 cyclones, and from 2008 to 2022, 24 cyclones formed. While the frequency has declined, the strength and destructiveness of these storms have risen sharply.

Explaining this paradox, Meteorologist Muhammad Abul Kalam Mallick of the Bangladesh Meteorological Department said, “Sea surface temperatures are rising, and land surface temperatures are also increasing. This is creating extreme environmental conditions, disrupting the patterns that usually lead to low-pressure systems or cyclones. As a result, the frequency of cyclones is going down, but the threat of major storms is increasing.”

A 2021 study titled “Exploring Past and Future Tropical Cyclones in the Bay of Bengal with High-End Computing” by the NASA Center for Climate Simulation (NCCS) echoed this observation. The study found that while the number of cyclones may decrease in a warming climate, more powerful cyclones - especially during the post-monsoon season - are likely to develop in the northern Bay of Bengal, threatening Bangladesh, India, and Myanmar.

The Intergovernmental Panel on Climate Change (IPCC) has also reported a similar trend: the number of severe cyclones in the Bay is rising. BUET’s Professor AKM Saiful Islam, who has worked with the IPCC, explained, “Although the frequency of cyclones is decreasing, those that are forming are becoming more intense - and this trend may worsen. A 1°C rise in global temperatures increases the air’s water-holding capacity by 7 per cent. That means heavier rainfall and stronger storms.”

Experts believe that the recent MIT study could play a critical role in strengthening early warning systems and guiding sustainable development planning in Bangladesh’s coastal regions.

The study warns that Bangladesh now urgently needs a comprehensive, risk-based disaster strategy. It states, “Current infrastructure investments are largely based on historical climate data. But many regions and communities remain dangerously exposed. If we continue to plan based on the past, without adjusting our design standards, policies, and financial frameworks to reflect future disaster risks, we will keep building for a world that no longer exists.”

Bangladesh’s main policy for addressing climate change - the Bangladesh Climate Change Strategy and Action Plan (BCCSAP) - was adopted in 2009. At the time, it was a major step. However, in the years since, the landscape of climate challenges has evolved dramatically. New research has revealed additional risks, losses, and threats.

Climate expert Hasib Muhammad Irfanullah, who has long been involved in climate change research, said, “The BCCSAP is now outdated. Unfortunately, it is still the foundation for much of our future planning. Even the projects being approved today are based on it. Although Bangladesh adopted the National Adaptation Plan (NAP) in 2022, we haven’t begun implementing it meaningfully. We’re holding it in our hands but not putting it to work.”

The structural, planning, and design reforms recommended in the MIT study have also been endorsed by the country’s disaster specialists.

Gawher Nayeem Wahra, a disaster risk expert, said, “Perhaps the most striking finding of the MIT study is how much the average return period of storm-tides has changed. This shift means the timing, severity, and location of hazards will also change. Familiar cyclones and floods may no longer behave in familiar ways. The survival skills passed down through generations in coastal communities might no longer be effective. This demands area-specific, seasonal, and continuous research and observation.”

Bangladesh has made major strides in cyclone preparedness since the devastating 1991 cyclone, which killed hundreds of thousands when it coincided with a high tidal surge. In the decades since, early warning systems, cyclone shelters, and community awareness have vastly improved. However, Gawhar Nayeem Wahra warned that complacency has crept in, particularly because the country has not faced a catastrophic cyclone in recent years.

To address long-term climate challenges, the government has already developed the Delta Plan 2100, a strategic blueprint for managing floods, water supply, erosion, river systems, and drainage across Bangladesh. Climate change adaptation is a key pillar of that plan.

However, climate scientists like Professor AKM Saiful Islam say that the Delta Plan now needs to be updated in light of the MIT study and other recent findings.

The Delta Plan is supposed to be reviewed every five years. In the next review, these new results must be incorporated to make our future plans more realistic and responsive to the emerging climate scenario, he added.

[Information provided by Kalyan Banarjee, Satkhira and Ruhul Bayan, Maheshkhali, Cox’s Bazar]

* The report, originally published in the print and online edition of Prothom Alo, has been rewritten in English by Farjana Liakat