A 2.4-metre (7.9-foot) surge from Cyclone Nira drove salt water deep into the Indian Sundarbans last month, pushing 620 sq km (239 sq miles) of mangrove forest past a threshold that scientists say could bring years of accelerating decline. The finding comes from field measurements assembled after the cyclone and points to a crisis hidden beneath a canopy that still looks largely green from above.
A team led by estuarine ecologist Pia L. Padmasari says 19 of 31 monitoring sites stayed above a critical soil-salinity level for at least 120 consecutive days, a duration linked to failed regeneration of the salt-sensitive sundari tree. The threshold was crossed on 24 October, two days after Nira’s surge reached the tidal creeks around Satjelia.
Padmasari’s team spent six months measuring water and soil across islands in South 24 Parganas district, then checked the results against seedling counts and satellite images. At 14 sites, they found no young sundari trees that had survived the previous two monsoons. The analysis, reviewed by The Plausible Post, is being prepared for submission to a peer-reviewed estuary journal.
The canopy conceals a retreat
The official forest maps reviewed by the researchers still class most of the affected belt as stable mangrove cover. But those maps measure canopy, not whether the forest can replace trees as old ones die. Field checks found salt-damaged soil beneath intact crowns, while newly exposed mud banks showed where creek edges had begun to retreat.
“The forest can look green for years after it has stopped making its next generation,” said Ivo Zíka, a geomorphologist who reviewed the measurements. He called the change a local ecological tipping point, not proof that the entire Sundarbans is doomed. “Once seedlings fail and banks erode, the next surge reaches farther inland.”
The forest can look green for years after it has stopped making its next generation.
Ivo Zíka, geomorphologist
The researchers’ worst-case projection, if dry-season freshwater flows keep falling, is that another 185 sq km (71 sq miles) could lose dense mangrove cover by 2040. They estimate that up to 1.1 million people on low-lying islands could face longer shortages of usable freshwater by 2035. The figures are scenarios, not forecasts, and depend on how quickly water managers restore freshwater to the creeks.
Scientists seek emergency measures
Padmasari’s team is urging authorities to arrange a freshwater pulse through existing sluices before January, when dry-season salinity usually climbs, and to protect remaining freshwater pockets from new drainage cuts. State officials have discussed both measures, but have not announced a release schedule. Local farming and drinking-water supplies also depend on the same limited freshwater.
Jaka Košir, a spokesperson for the state’s coastal department, said the forest remained intact across most of the mapped area and that the measurements did not justify describing the whole delta as irreversibly damaged. “There is no immediate threat to residents, and our routine monitoring continues,” he said. Zíka countered that a green canopy is a poor guide to future protection from tides.
The cyclone did not create the underlying salinity trend, which researchers say has been building through weaker freshwater flows and rising seas. But it pushed the monitored sites across the duration threshold in a matter of days. Scientists say the next dry season will test whether emergency water releases can still give the forest a chance to regenerate.
