The Sundarbans at the crossroads of climate change and human survival [Commentary]

Spanning India and Bangladesh, with India comprising 40% of its area, a vast and ever-shifting mangrove forest stretches across the Bay of Bengal. This vast delta derives its name from the Sundari (Heritiera fomes), the tall mangrove species that flourishes here in abundance. The name “Sundarbans” is a modern rendering of “Sunderbunds,” a term coined by Walter Hamilton in the East India Gazetteer, meaning “Forests of the Soondry” (“Sundri,” or beautiful). Heritiera fomes is the abundant tall mangrove species of the region. Where the rivers Ganga (Padma in Bangladesh), Brahmaputra, and Meghna discharge into the Bay of Bengal, they form the Sundarbans — the largest contiguous mangrove forest on Earth. Toward the coast, the forest transitions into a low-lying swamp of sand dunes, mud flats, and barren expanses, intersected by innumerable tidal streams and channels. Four protected areas within this remarkable landscape are recognised as UNESCO World Heritage Sites: Sundarbans West, South, and East in Bangladesh, and Sundarbans National Park in India.

The nutrient-rich mangrove waters of India’s eastern coast form a vital breeding ground and nursery for roughly 90% of the region’s aquatic species. The ecosystem is notable for supporting overlapping populations of threatened aquatic mammals, including the Ganges river dolphin and the Irrawaddy dolphin. This extraordinary species concentration in the Sundarbans stems from the dynamic mixing of freshwater from major rivers — the Ganga and the Brahmaputra among them — with the saltwater of the Bay of Bengal.

As Amitav Ghosh writes in his 2004 book The Hungry Tide, a novel set in the Sundarbans, in a delightful blend of science and poetry: “The proliferation of aquatic life was thought to be the result of the unusually varied composition of the water itself. The waters of rivers and sea did not intermingle evenly in this part of the delta; rather, they interpenetrated each other, creating hundreds of different ecological niches, with streams of freshwater running along the floors of some channels, creating variations of salinity and turbidity. These micro-environments were like balloons suspended in the water, and they had their own parameters of flow… each balloon was a floating biodome filled with endemic fauna and flora… responsible for creating and sustaining a dazzling variety of aquatic life forms — from gargantuan crocodiles to microscopic fish.”

This amphibious landscape, neither fully land nor fully water, functions almost as a character in its own right in Amitav Ghosh’s novel, dictating the rhythms of daily life through its relentless cycles of tide, erosion, and cyclones. Centred on a U.S.-trained marine biologist who explores the waters of the Sundarbans in search of river dolphins, the novel revolves around the unpredictable and often violent power of the tides and wildlife — forces that shape human survival in ways both intimate and absolute. In the Sundarbans, the boundary between human habitation and untamed nature is perilously thin: a cyclone may swallow a village overnight, and a fisherman may fall prey to a tiger before reaching shore. Against this backdrop, Ghosh stages a profound tension between the impulse to protect the environment and the urgent need to sustain the basic survival of the region’s inhabitants. Conservation efforts, however well-intentioned, frequently collide with the livelihoods of those who depend on the forest’s resources to eat, fish, and earn a living.

This tension is deepened by the region’s layered history. Although the migration of labourers to Sundarbans started during the British Colonial rule, the Indian part of the Sundarbans eventually became a refuge for migrants who crossed the border in the turbulent early years of India’s partition and in the later periods, in search of land, security, and a place to belong. These deprived survivors carved out lives on fragile, newly formed islands, living in constant negotiation with the nature and its creatures or even with the fraught regional politics. In this sense, the landscape itself becomes an epic: a living chronicle of how humans, animals, and forests have survived side by side through conflicting interests, fragile compromises, and at times, intuitive, unspoken forms of cooperation.

A product of nature’s engineering

Home to the endangered royal Bengal tiger, the Sundarbans is the largest single tract of mangrove forest in the world. It is not only a haven of biodiversity but also a region shaped by a fascinating geological history. This unique landscape, which spans Bangladesh and West Bengal, owes its existence to a complex interplay of geological processes and climate that have been at work for millions of years.

The rising Himalayas during the Tertiary Period (66 million to 2.6 million years ago) had far-reaching consequences — not just for the subcontinent but for the entire region. This uplift set the stage for the stabilisation of the monsoon regime, the evolution of great rivers, and sediment transportation. These processes led to the development of the Bengal Delta, the foundation of the Sundarbans.

During the Early Holocene (around 11,000 to 7,000 years ago), rapid melting of glaciers caused a global eustatic sea-level rise. The sea advanced far inland into the Bengal Basin, creating a massive amount of “accommodation space” (underwater volume available for sediment). During this rapid transgression phase, rivers could not deposit sediment fast enough to build permanent land. As a result, the area remained an open marine or estuarine environment rather than a subaerial deltaic forest.

The evolution of the Sundarbans — the world’s largest mangrove forest, located within the Ganga-Brahmaputra Delta — is fundamentally linked to the stabilisation and eventual slowing of sea-level rise during the mid-to-late Holocene (roughly 5,000 to 2,000 years ago). The primary geological and ecological mechanisms driving this connection are as follows:

Between 5,000 and 2,500 years ago, the rate of global sea-level rise decelerated sharply, nearing its present position. In parts of the Indian subcontinent, this period was characterised by a relative regression (withdrawal) of the sea from its maximum inland reach. As the sea stabilised or retreated seaward, the colossal volume of sediment carried down by the Ganga and Brahmaputra rivers finally began to outpace the ocean’s depth. This allowed the delta to build outward (prograde) toward the Bay of Bengal, forming a series of overlapping, eastward-progressively younger deltaic lobes that created the physical landmass of the modern coastal plain.

Mangroves cannot establish themselves in deep open oceans or on high-energy coastlines. The withdrawal and stabilisation of the sea during the late Holocene created the precise geomorphic features required for the Sundarbans mangrove ecosystem. The retreat of the sea exposed extensive low-lying, flat mudflats and shallow estuaries. These mudflats experienced regular, gentle inundation by semi-diurnal tides. This mixed fresh river water with saline seawater, generating the specific brackish salinity conditions that unique mangrove species (such as Heritiera fomes and Phoenix paludosa) require to outcompete normal terrestrial vegetation.

The evolution was further modified by the unique tectonics of the Bengal Basin. As the delta built outward during the late Holocene, tectonic tilting slowly shifted the primary flow of fresh water eastward. The western part of the delta (where the modern Sundarbans sits) became “fluvially abandoned” by the main river courses, leaving it completely dependent on tidal processes and the geological framework established during the mid-Holocene sea-withdrawal.

A region on the frontlines of climate change

At the head of the Bay of Bengal, where three great rivers — the Ganga (Padma in Bangladesh), the Brahmaputra, and the Meghna — pour into the sea, lies a vast amphibious landscape unlike any other on Earth. The Sundarbans, the world’s largest river delta, is a realm where land and water intertwine, where mangrove forests shelter Bengal tigers, and where millions of people have built their lives on shifting, low-lying islands. Today, however, this remarkable region faces an existential threat: the rising sea and the dwindling flow of sediment that once kept the delta alive.

The Indian Sundarbans has become a major source of climate-induced displacement and distress migration in India. The forces driving this exodus are relentless: rising sea levels, increasingly frequent cyclones, and soil salinisation that renders agricultural land barren and destroys fishing livelihoods. The waters of the delta are rising faster than the global average, submerging islands and eroding coastlines. Severe cyclonic storms have routinely breached embankments and flooded villages, leaving behind a trail of destruction.

Saltwater intrusion has contaminated both agricultural land and freshwater sources, crippling the traditional farming and fishing economies upon which local communities depend. The region also endures extreme seasonal swings. During the monsoon, flooding and waterlogging are widespread, and salinity drops to its lowest annual levels. In summer, freshwater becomes scarce, and salinity soars to dangerous highs. This dramatic range of salinity threatens both the region’s unique flora and fauna and makes livelihoods extraordinarily difficult to sustain at the household level and across the entire ecosystem.

Data compiled from NASA Landsat satellite imagery reveal a sobering picture: over the past two decades, sea levels in the Sundarbans have risen at an exceptional average rate of about 3 centimetres per year — significantly higher than the global average. Over the past 40 years, the region has lost nearly 12% of its shoreline to severe coastal erosion.

Three interconnected forces are driving this ecological emergency: accelerated sea-level rise, fuelled by global climate change and thermal expansion in the Bay of Bengal; land subsidence, as the deltaic landmass gradually sinks, compounding the relative rise in water levels; diminished sediment supply, caused by upstream dams and river interventions that have drastically reduced the natural deposition needed to replenish and stabilise the shoreline; and reduced access to freshwater, caused primarily by the construction of structures like the Farakka Barrage and regional water withdrawals or damming have drastically reduced the natural flow of freshwater from the Ganges-Padma river system into the delta.

As the climate continues to change, widespread flooding is expected across this low-lying region, which is home to approximately 7 to 7.5 million people — 4.4 to 4.5 million in India and 2.5 to 2.7 million in Bangladesh. Already, several islands have been completely submerged, displacing thousands of inhabitants and creating a growing population of climate refugees. Environmental migration lacks standing in international treaty law, and no national provisions support or compensate for migration from the Sundarbans. India’s disaster risk policies cover only relief for extreme-weather events, not displacement from environmental stress. Environmental change is also hard to isolate from other migration drivers. Research shows environmental migration is multicausal — poverty, socio-political insecurity, and environmental dangers reinforce one another. This holds in the Indian Sundarbans, where living standards are dire: a post-cyclone household survey found 510 of every 1,000 residents, mostly children, malnourished or suffering from waterborne and communicable illnesses, and a severe crisis of childhood drowning.

Amphibious living

Faced with rising salinity, unpredictable flooding, and mounting migration pressures on both the Indian and Bangladeshi sides of the Sundarbans, researchers and communities are exploring a bold adaptive response: Amphibious Living Opportunities (ALO). This approach combines resilient housing, diversified climate-adapted livelihoods, and community-driven initiatives. Proposed measures include disaster-resilient farming, fisheries, and cooperative efforts supported by capital, technology, and institutional partnerships. The goal is ambitious but essential — to secure sustainable futures for the vulnerable island communities that call this amphibious land home.

The Sundarbans stands at a crossroads. Without concerted action, this extraordinary delta — a cradle of biodiversity and human resilience — may gradually slip beneath the waves. The Amphibious Living Opportunities framework offers a path forward, but its success will depend on sustained investment, institutional commitment, and the active participation of the communities most at risk. For the millions who live at the water’s edge, the stakes could hardly be higher. Ultimately, as Amitabh Ghosh’s novel The Hungry Tide asks, whether compassion and coexistence are possible in a world where nature gives and takes without warning.

Banner image: Residents of Satyanarayanpur village in South 24 Parganas district, West Bengal, push their boat into the waters of Sundarbans. Sea level rise is eating away at the islands of the Sundarbans in India and Bangladesh. Photographed in 2015. (AP Photo/Bikas Das)

The author is an adjunct professor at the National Institute of Advanced Studies, Bengaluru.

Citation:

• Amitav Ghosh, 2004. The Hungry Tide. Penguin Random Books, India, 430p.
• Aziz, A. and Paul, A.R. 2015. Bangladesh Sundarbans: Present Status of the Environment and Biota. Diversity, 7, 242-269; doi:10.3390/d7030242
• Hait, A.K.  and Behling, H. 2019. Responses of the mangrove ecosystem to Holocene environmental change in the Sundarban Biosphere Reserve, India.
• Acta Palaeobotanica, 59 (2), 391-409.