Bangladesh could face a new reality with climate change. Storm tides are likely to increase 10-fold: Study

Destructive storm tides are likely to increase 10 times in Bangladesh in response to climate change, warned a new study published in the journal One Earth.

A storm tide is defined as high water level caused by the combination of a normal astronomical tide and a storm surge (abnormal rise in sea level due to a tropical cyclone or other intense storm). This could lead to coastal flooding.

The destructive storm tides, which used to occur once in every 100 years, is likely to become more frequent, hitting Bangladesh once every decade.

“Our study shows that under high-emissions scenarios, such extreme storm tides may occur every decade or even more frequently, not because cyclone counts increase dramatically, but because stronger storms and higher seas amplify flood impacts,” study co-author Sai Ravela, principal research scientist in the Massachusetts Institute of Technology’s Department of Earth, Atmospheric and Planetary Sciences, told Down To Earth.

Bangladesh's low-lying coast, home to some eight million people, is vulnerable to tropical cyclones and storm tides, with high mortality. Six tropical cyclones in the Bay of Bengal have each killed more than 140,000 people, primarily due to coastal flooding of the low-lying, densely populated mega-delta.

Combining storm surge with astronomical tide and sea-level rise captures some of the most destructive elements of coastal flooding, Ravela explained.

However, a lack of accurate storm tide risk assessments under future climate conditions hinders the country’s ability to adapt and build resilient infrastructure.

“Our study addresses this gap using perhaps one of the only approaches that can downscale large numbers of synthetic cyclones in future climate scenarios from climate models that poorly resolve tropical cyclones,” Ravela explained. The researchers simulated tens of thousands of potential tropical cyclones near Bangladesh under several future emission scenarios — from business as usual to high emissions scenario due to fossil fuel combustion. 

For each simulation, they recorded the highest number of storm tides and the frequency of such tides of various heights in a given climate scenario.  The researchers found that storm tides could recur once every decade under a high emission scenario.

Further, Bangladesh is also likely to see another unusual pattern if the planet continues to warm: Tropical cyclones overlapping with the monsoon season by the end of the century. This will not give people any respite. 

So far, the country witnessed cyclones and the monsoon at separate times during the year. While the monsoon occurs in summer, between June to September, tropical cyclones in the Bay of Bengal typically peak in the pre-monsoon between May and June and post-monsoon from October–November, Ravela explained.

Climate change, he added, may delay monsoon withdrawal and prolong warm sea surface temperatures. “This could create a transitional ‘shoulder season’ where monsoonal conditions persist while cyclone-favourable conditions emerge,” he explained.

Reduced wind shear and altered atmospheric circulation could make conditions ripe for late-season cyclones to form while monsoon-related soil saturation and river loading are still active, the expert observed. “This raises the risk of compound flood events, where both systems interact to worsen impacts,” he warned.

The researchers next plan to translate these projections into decision-making tools, helping local communities and national planners carry out on-the-ground adaptation and mitigation.