As climate change intensifies, the tide of a 100-year storm to hit Bangladesh every ten years, scientists report

Tropical cyclones are hurricanes that can brew tropical oceans and run on land, allowing coastal areas to flood. The most extreme cyclones can produce catastrophic storm tides. This is the seabed that is elevated by the tide, swells on land, causing catastrophic flood events in coastal areas.

A new study by MIT scientists finds that as the planet warms up, the recurrence of destructive storm tides increases by 10 times in one of the world’s most difficult regions.

In a study published in One Earth, scientists report that in the highly populated coastal state of Bangladesh, once 100 years of events can attack every decade or more frequently by the end of the century.

In the future where fossil fuels continue to burn as they do today, what was once considered a catastrophic and once-in-a-century storm tide hits Bangladesh every decade on average. And the types of storm tides that have emerged every decade can knock down the country’s coast more frequently every few years.

Bangladesh is one of the world’s most densely populated countries, with over 171 million people living in a nearly-sized area of ​​New York.

The country has historically been vulnerable to tropical cyclones. Because it is a lowland delta that is easily flooded by storms and experiences seasonal monsoons. Some of the world’s most devastating floods have occurred in Bangladesh, making the agricultural economy increasingly difficult to recover.

The study also found that Bangladesh is likely to experience a tropical cyclone that overlaps with the months-long monsoon season. Until now, cyclones and monsoons have occurred at separate periods of the year. But as the planet warms, scientists’ modelling shows that cyclones are pushed into monsoon seasons, causing consecutive flood events across the country.

“Bangladesh is very active in preparing for climate risks and risks, but the problem is that what they’re doing is more or less based on what they see in the current climate,” says research co-author Sai Lavera, a leading research scientist at MIT’s Earth, Atmospheric and Planetary Science (EAPS).

“We are now seeing the recurrence of devastating storm tides rising almost 10 times, almost everywhere in Bangladesh, which cannot be ignored, so I think this is timely.

Ravela co-authors are EAPS postdoc Jiangchao Qiu and Kerry Emanuel, professor emeritus of atmospheric science at MIT.

Tide height

In recent years, Bangladesh has invested heavily in preparing for the storm. For example, in improving early warning systems, strengthening village levees, and increasing access to community shelters. However, such preparations are generally based on the current frequency of the storm.

In this new study, the MIT team aims to provide a detailed prediction of the dangers of extreme storms, a flood event in which Bangladesh’s tide effects amplify cyclone-induced storm surges, under various climate warming scenarios and projections during sea level rise.

“A lot of these events happen at night, so depending on what the tide is, the tide plays a very strong role in how much extra water you get,” explains Lavera.

To assess the risks of Storm Tide, the team first applied a physics-based downscaling method. It was first developed by Emmanuel’s group over 20 years ago and is used to study hurricane activity in various parts of the world.

This technique includes low-resolution models of the world’s oceans and atmospheres, embedded with finer resolution models that simulate weather patterns as detailed as a single hurricane. The researchers then scatter hurricane “seeds” in the area of ​​interest and run the model forward to observe which seeds grow and land over time.

In the downscale model, researchers incorporated a hydrodynamic model that simulates the height of the storm surge, taking into account the wind patterns and strength at a particular storm time point. For certain simulated storms, the team also tracked the effects of tide and sea level rise, and incorporated this information into a numerical model that calculated the tide or water height of the storm, landing the tide effects as storms.

Extreme overlap

With this framework, scientists have simulated tens of thousands of potential tropical cyclones near Bangladesh under several future climate scenarios.

For each simulation, they recorded the largest storm tides along the coast of Bangladesh, noting the frequency of storm tides of various heights in certain climate scenarios.

“We looked at the whole bucket of simulation and saw this lot of storms, three metres, for this tide of storms. Then we can get a sense of the relative frequency of those kinds of storms,” ​​says Qiu. “The number can then be reversed into the return period.”

The return period is the amount of time it takes for a certain type of storm to land again. Storms considered “100 Year Events” are usually more powerful and destructive, and in this case produce more extreme storm tides and therefore more devastating floods compared to 10 Year Events.

From their modelling, Labella and his colleagues discovered that under the scenario of increasing global warming, storms previously considered a 100-year event create the value of the best storm tides, and could recur within ten years by the second half of the decade. They also observed towards the end of this century that tropical cyclones in Bangladesh emerged across wider seasonal windows, potentially overlapping with seasonal monsoon seasons in certain years.

“If monsoon rain comes in and saturates the soil, the cyclones come in, making the problem even worse,” says Labella. “People have no reprieve between extreme storms and monsoons. There are so many combined and cascaded effects between the two. This only manifests itself as a result of global warming.”

Lavera and his colleagues use modeling to help Bangladeshi experts better assess and prepare for the future of increased risk of storms. And he says that the future of Bangladesh’s climate is not unique to this part of the world.

“This climate change story unfolds in Bangladesh in a certain way is played differently elsewhere,” Lavera points out. “Maybe where you are, the story is about heat stress, amplification of droughts, or wildfires. The dangers are different. But the underlying catastrophe stories aren’t that different.”

This story has been republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and education.