TN coastline might face 78 cm sea-level rise by 2100, finds study

CHENNAI: A study on sea-level rise along India's 7,500 km coastline has warned that Tamil Nadu's crowded shores and low-lying deltas are among the most vulnerable stretches in the country.

The assessment, led by Professor Ramachandran of the Centre for Climate Change and Disaster Management at Anna University, combines three decades of tide-gauge and satellite data with the latest climate model projections to outline risks and district-level vulnerabilities.

Across India, the study projects that the sea could rise by about 25 cm in a low-emission future and more than a metre under high emissions by 2100. Low emissions assume the world cuts back sharply on greenhouse gases, while high emissions reflect "business-as-usual" pollution levels.

For people living on the shore, the difference could determine whether seas slowly edge upward or whether they reshape homes, fields and livelihoods within a lifetime.

To sharpen the findings, the researchers divided the coast into 247 sites at four-kilometre intervals and then averaged the results at the district level. This approach captures local variations, something especially important in Tamil Nadu, where the sea has not been rising evenly.

When the researchers ran their models, they found that under high-emission scenarios, the Tamil Nadu coast could see up to 78 centimetres of rise by the end of the century.

In flat, deltaic districts like Nagapattinam and Cuddalore, even a few additional centimetres of water could mean the difference between water stopping at the edge of a field and water travelling several kilometres inland.

Meanwhile, for Chennai, tide gauges from 1992 to 2022 show the city is recording a steady upward trend of a few millimetres each year; annually, it's the thickness of a coin, which becomes more than a hand's length over a few decades.

Nagapattinam too shows a rising trend, while Thoothukudi records a slight fall, which the authors attribute to land uplift in the area. But the report warns that such differences do not reduce the overall threat, as what matters for communities is how long-term sea-level rise combines with cyclones, storm surges and saltwater intrusion.

The study also highlights how cyclones magnify these risks. Between 1991 and 2023, the Bay of Bengal produced 62 cyclonic systems compared with just nine in the Arabian Sea. About two-thirds of severe cyclones were formed after the monsoon, when the seas are warmest.

Saltwater intrusion is already being reported along Tamil Nadu's coast. Wells that once yielded fresh water are turning brackish, affecting both drinking supplies and irrigation. With Tamil Nadu having the second-longest coastline in India and one of the largest fishing populations, these changes threaten not just water security but also farming and fisheries. The report notes that ports such as Chennai and Thoothukudi, along with shrimp farms and seafood processing units, are also exposed to inundation and salinity changes.

For adaptation, the authors argue that Tamil Nadu will need a mix of hard structures and natural buffers. Seawalls in parts of Chennai, mangroves and wetlands such as Pichavaram and Muthupet can act as natural barriers, absorbing wave energy and reducing surge impacts. At the community level, the study calls for stronger early warning systems and, in the long run, difficult conversations about relocating the most exposed villages.

Dark cloud on the coast

Between 1991 and 2023, the Bay of Bengal produced 62 cyclonic systems compared with just nine in the Arabian Sea

In flat, deltaic districts like Nagapattinam and Cuddalore, even a few additional centimetres of water could mean the difference between water stopping at the edge of a field and water travelling several kilometres inland

For Chennai, tide gauges from 1992 to 2022 show the city is recording a steady upward trend of a few millimetres each year; annually, it's the thickness of a coin, which becomes more than a hand's length over a few decades

Ports such as Chennai and Thoothukudi, along with shrimp farms and seafood processing units, are also exposed to inundation and salinity changes