Sundarbans loses coastline as sea rises faster than global average

The Sundarbans, the planet’s largest mangrove forest, is losing nearly a dozen percent of its coastline as sea water climbs about three centimetres each year, outpacing the world average. The forest spans the delta of the Ganga, Brahmaputra and Meghna rivers, covering Bangladesh and the Indian state of West Bengal, with India holding roughly 40 % of the area. Freshwater from these rivers mixes with salty Bay of Bengal water, creating brackish zones that nurture about ninety percent of the region’s fish and support threatened dolphins such as the Ganges and Irrawaddy species. The mangrove habitat also shelters the endangered Royal Bengal tiger and a host of other wildlife. Four zones within the delta – three in Bangladesh and one in India – are listed as UNESCO World Heritage sites. Rapid sea‑level rise, stronger cyclones and saltwater intrusion are forcing villages to drown, farms to turn barren and fishermen to lose their catch. Over the last forty years the shoreline has receded by almost twelve percent, prompting a wave of climate‑driven migration from the Indian side of the Sundarbans. Historically, people settled here during British rule and later after Partition, carving homes on fragile islands while constantly negotiating with tides and predators. Conservation projects often clash with the need of locals to harvest wood, fish and farm the land. The landscape’s future now hinges on slowing sea rise and restoring sediment flow to rebuild the delta’s protective mudflats.

Background

The forest sits on a delta formed when the rising Himalayas during the Tertiary period set up the monsoon and fed massive rivers with sediment. After a rapid sea‑level surge in the early Holocene left the basin underwater, the rise slowed around five thousand years ago, allowing river deposits to catch up and push land outward. The retreat created shallow mudflats and tidal channels where mangroves like Heritiera fomes and Phoenix paludosa could take root.

Context

Mangroves need low‑energy, brackish water; the Sundarbans’ unique mix of fresh and salty tides creates the perfect conditions for its rich biodiversity. The same mix also makes the area highly sensitive to changes in sea level and salinity, which is why climate shifts pose such a severe risk.