CHENNAI: Tamil Nadu could face a sea-level rise of up to 78.15 cm by 2100 under high-emission scenarios, a new study has projected. The research, published in Theoretical and Applied Climatology (2025), assessed risks along India’s coastline using historical data and future climate models.
The study was led by A Ramachandran, emeritus professor at the Centre for Climate Change and Disaster Management, Anna University. He told TNIE that the team analysed satellite altimetry data from the US-based National Oceanic and Atmospheric Administration (NOAA) between 1992 and 2023, along with tide gauge records from the Permanent Service for Mean Sea Level (PSMSL).
“Future projections were developed using SimCLIM software in line with the IPCC Sixth Assessment Report (AR6). Data from 39 global climate models were applied to simulate sea-level rise under different Shared Socioeconomic Pathways (SSPs). Projections were calculated for 247 coastal points spaced every 4 km and aggregated at the district-level for states including Tamil Nadu,” Ramachandran said.
Tide gauge stations in Tamil Nadu show uneven trends: Thoothukudi recorded (-) 0.17 mm per year, Nagapattinam 0.18 mm per year, and Chennai 0.55 mm per year. Researchers said that while short-term variations exist, the long-term trend shows an overall increase, consistent with global and Bay of Bengal patterns.
Nagapattinam is the most vulnerable district due to its low-lying topography and multiple river confluences that amplify flooding and erosion. Coastal stretches of Tiruvarur, Cuddalore, and parts of Chennai are also exposed to the risk, Ramachandran said.
One of the key drivers of rising sea levels is thermal expansion, where warming seawater expands in volume. Tamil Nadu is particularly sensitive to this change because of its warm surface waters and high freshwater inflows. Researchers noted that while land subsidence and glacier melt contribute to the trend, thermal expansion is continuous and will keep pushing levels upward even if ice loss slows.
The state’s cyclone-prone coastline adds to the risk. Between 1991 and 2023, the Bay of Bengal recorded 62 cyclones compared to just nine in the Arabian Sea, with 67% of severe cyclones occurring in the post-monsoon season. Rising seas will further increase storm surge flooding in coastal districts. Saltwater intrusion into groundwater is already being reported in parts of Nagapattinam and Thanjavur, threatening irrigation and drinking water security.
The study suggests a mix of hard infrastructure such as seawalls and surge barriers, along with nature-based solutions like mangrove restoration and living shorelines. Community participation and local-level planning, it said, will be critical. Ramachandran added that the study, partly supported by the Tamil Nadu Climate Change Mission, underlines the need for district-specific strategies to manage both long-term sea-level rise and short-term storm surge risks.