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Ripples from Cyclones and tides in Sunderbans


Over just the past three years from 2018-2021, the Sunderbans, which is home to close to five million people, has been battered by four tropical cyclones — Fani (May 2019), Bulbul (November 2019), Amphan (May 2020) and Yaas (May 2021).

On each occasion, the region has suffered damage because of gale winds and breached embankments, leading to ingress of sea water.


GS-I: Geography (Important Geophysical Phenomenon), GS-III: Disaster Management

Dimensions of the Article:

  1. What is a Storm Surge?
  2. Situation of Unprecedented Surge in Sunderbans
  3. Cyclone Yaas and High tide devastation
  4. Storm Surges and Coastal Communities

What is a Storm Surge?

  • A storm surge is a rise in sea level that occurs during tropical cyclones, intense storms also known as typhoons or hurricanes.
  • The storms produce strong winds that push the water into shore, which can lead to flooding. This makes storm surges very dangerous for coastal regions.
  • A storm surge is primarily caused by the relationship between the winds and the ocean’s surface. The water level rises where the winds are strongest. In addition, water is pushed in the direction the winds are blowing.
  • Due to Coriolis effect: if a cyclone develops in the Northern Hemisphere, the surge will be largest in the right-forward part of the storm. In the Southern Hemisphere, the surge will be largest in the left-forward part of the cyclone.
  • Another factor contributing to storm surge is atmospheric pressure. The pressure is higher at the edges of a cyclone than it is at the center. This pushes down the water in the outer parts of the storm, causing the water to bulge at the eye and eye wall—where the winds have helped add to the rise in sea level.
  • More factors contribute to the strength of a storm surge as the dome of water comes ashore. The water level can reach as high as 10 meters if the storm surge happens at the same time as high tide.

Situation of Unprecedented Surge in Sunderbans

  • For people in the ecologically fragile Sunderbans, life revolves around battling high tides daily and cyclones regularly. But every cyclone throws up new challenges to the Sunderbans and its inhabitants — something the people had not imagined, and policy makers are not prepared for.
  • The intensity of the gale winds has ranged from 100 kmph to 150 kmph during each of the cyclones – Fani, Bulbul, Amphan and Yaas.

Cyclone Yaas and High tide devastation

  • Though Cyclone Yaas made landfall about 200 km south of the Sunderbans in Odisha, it inundated (flooded) large areas of the estuary. The cumulative effect of the full moon tide and the cyclone led to the overflowing and breach of embankments in large areas of the Sunderbans.
  • While the India Meteorological Department had predicted a storm surge of 2 m above the astronomical tide level, water in the river and bay swelled due to full moon tide. As a result, as Cyclone Yaas made landfall, large areas were inundated.
  • Three days after the cyclone, several areas of Sunderbans remain inundated, forcing people to huddle in cyclone shelters or spend days on embankments.
  • Ghoramara is one of the islands that has been sinking due to rising sea levels, where a few dozen houses and acres of land go under water every year. Even so, the residents were not prepared to see the entire island under water.
  • Another island in the western part of Sunderbans, the boat-shaped Mousuni, is also under water. Not only islands, but even coastal areas like Kakdwip, Namkhana and Frasergunj have been submerged.
  • Sagar Island, the biggest island of the Sundarbans chain and site of the famous Gangasagar Mela during Makar Sankranti, has also suffered damage.
  • Not only the western part of Sunderbans that faces Bay of Bengal but large parts in Gosaba and Sandeshkhali block, in the eastern part of the delta remain under water three days after the cyclone Yaas and the high tide.
  • Once the sea water enters the islands, not only are dwelling units destroyed but the crops are inundated and land cannot be cultivated because of the salinity, even the fish in the ponds die.

Click Here to read more about the Increasing numbers of cyclones in changing times

Storm Surges and Coastal Communities

  • Tropical cyclones, and the storm surges they generate, are a serious hazard for coastal areas in tropical and subtropical regions of the world. When a cyclone hits land, the accompanying storm surge will most often flood the surrounding coastal area.
  • Flooding is responsible for most deaths and economic damage associated with tropical cyclone landfalls.
  • Improvements in forecasting cyclones and issuing early warnings to the public have become indispensable as both coastal populations and the occurrence of extreme storms continue to rise. However, even sophisticated meteorology and storm warnings do not always protect against devastating storm surges.
  • Advance warning of a strong storm surge also allows homes and businesses to prepare for damage.

Wetlands as a “crush zone”

  • Coastal residents can reduce the damage done by a storm surge by protecting local wetlands. Wetlands, such as swamps, estuaries, and mud flats, act as sponges for tropical cyclones.
  • As the cyclone makes landfall, the marshy land and plants absorb the water and the energy of the storm surge. Silt and swamp vegetation prevent the most intense part of the storm surge from hitting homes and businesses.
  • The development of coastal wetlands for housing, industry, or agriculture reduces the natural barrier that wetlands provide. Communities can protect themselves against storm surges by maintaining healthy coastal wetland ecosystems.

-Source: The Hindu

February 2024