The Sundarbans (সুন্দরবন) is a mangrove forest that stretches across the southern part of Bangladesh and the eastern part of the West Bengal state in India. Located in the northern hemisphere just north of the Tropic of Cancer, it lies in a delta region created by the confluence of the Ganges, Brahmaputra, and Meghna rivers. The name "Sundarbans" is derived from the Sundari tree (Heritiera fomes), a mangrove species that is abundant throughout the forest.

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Geographically, the Sundarbans spans roughly 260 kilometers from west to east along the Bay of Bengal, starting from the Hugli River estuary in India and extending to the western segment of the Meghna River estuary in Bangladesh. The forest reaches up to 80 kilometers inland at its widest point. The total area of the Sundarbans, including both land and water, is approximately 10,200 square kilometers.

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This unique ecosystem is characterized by a complex network of tidal rivers, mudflats, and small islands, all of which are covered by dense mangrove forests. The region is located at the junction of freshwater from the rivers and saline water from the Bay of Bengal, creating a brackish water habitat. The terrain transitions into a low-lying swampy mangrove landscape near the coast, which features sand dunes and mudflats. Mangrove forests cover about two-fifths of the Sundarbans, while water constitutes nearly half of the entire area.

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The Sundarbans is home to 102 islands on the Indian side, with 54 of them inhabited. The population of the region is significant, with over 12 million people living here—around 4.5 million in India and 7.5 million in Bangladesh. For centuries, the fertile soils of this delta region have been heavily exploited by humans, with much of the land converted into agricultural use. However, there are still pockets of the original forest that remain.

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The area experiences four tidal cycles each day: two high tides and two low tides. This dynamic tidal movement plays a critical role in shaping the ecosystem.

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The climate of the Sundarbans is classified as subtropical Mediterranean. Wind speeds generally decrease moving eastward across the region. The western part of the forest, especially during April and May, experiences the highest wind speeds—up to 25 kilometers per hour. This period also coincides with the hottest and driest part of the year, at around 30°C. During these months, the winds contribute to significant changes in the coastal sand formations. 

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Approximately 40% of the Sundarbans is covered by water, making it the largest mangrove wetland in the world. The ecosystem and landscape of this mangrove forest are intricately shaped by the network of rivers, creeks, and canals. Given the region's delicate hydrological system, any disruption in the flow of water can severely affect the entire ecosystem, as well as the livelihoods of the local population and the overall development of the Sundarbans.

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The Sundarbans provides a habitat for 84 species of plants, including 26 species of mangroves. It is also home to a rich diversity of wildlife, with 453 species of animals, 120 species of fish, 290 species of birds, 42 species of mammals, 35 species of reptiles, and 8 species of amphibians.

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Over time, however, the once intricate network of rivers that sustained this ecosystem has been significantly altered. Human interventions upstream in both Bangladesh and India have led to the disconnection of several rivers. This has resulted in reduced water flow, causing some rivers to dry up or carry much less water. As a result, the region's freshwater supply has been negatively affected, which in turn disrupts the delicate balance of the ecosystem.

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To combat flooding, salinity intrusion, and soil erosion, a series of embankments were constructed in the western part of the Sundarbans during colonial times and later in the 1900s.Deforestation of the Sundarbans was different than elsewhere in British India as the lands cleared for rice cultivation required temporary earthen embankments. These were constructed in the dry season to stop saline tidewater from ruining crops. Cultivators then breached these embankments during the monsoon to facilitate borsha floods that inundated the land with silt-laden river water mixed with rain. The silt fertilized the soil and naturally raised land levels, while the floods irrigated the rice fields and provided a breeding ground for fish.

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The Sundarbans hydrological balance has always depended on the steady flow of freshwater from upstream rivers, which helps to counteract the salinity from the tides. This delicate balance is critical for the growth and reproduction of aquatic plants and animals in the region. If the freshwater flow is reduced or the water becomes too saline, the entire ecosystem is at risk. The mangroves of the Sundarbans are uniquely adapted to the fluctuating salinity levels of the water, which is essential for maintaining the overall health of the forest.

 

References: 

“Landscape Narrative of the Sundarban: Towards Collaborative Management by Bangladesh and India”=Contributors: Bushra Nishat, AJM Zobaidur Rahman, Sakib Mahmud, et al