Effects of sea level rise on Tamil Nadu coast

Published in The Hindu on November 18, 2010

Tamil Nadu has a coastline that is 1,076 km long, and most of the vital installations and infrastructure, are located along the coast, not to mention the mangroves. While the quantum of sea level rise is being debated, the fact that sea level would rise due to global warming is not doubted.

Even by the conservative estimate of 1 m rise in the next forty years, nearly 2,000 square kilometres along the coast would be permanently inundated. But the total area at risk would be six times as much.

The preliminary analysis is based on a report to be published by the Chennai based the Institute for Financial Management and Research (IFMR).

The estimate is based on a preliminary analysis of the replacement value of major infrastructure, cost of wetland damage, and the market value of land at risk from a conservative estimate of 1 metre rise in sea level by 2050.

The study has not looked into the impact on human population. And the study aims to be “indicative, rather than comprehensive” of the risk from 1 m sea level rise (SLR) by 2050.

Though sea level rise would be uniform along the coast, five coastal districts — Nagapattinam, Thiruvarur, Thanjavur, Pudukottai and Ramanathapuram — appear to be at a greater risk. The reason: very high storm surges that already affect these districts. Accordingly, even areas that are below 10 m above current mean sea level are at risk from the 1 m sea level rise.

“For example, if the storm surges are six metres high, then we add 1 metre of sea level rise to it and then add 10 per cent of six metres to estimate for storm surge intensity to estimate the maximum storm surge,” said Dr. Sujatha Byravan from Centre for Development Finance, IFMR. Dr. Byravan is the lead author of the report.

According to her, with global warming and increased sea level rise, storm surges become more intense. Hence 10 per cent addition for storm surge intensity is done.

But actual height of storm surges can be calculated only based on detailed analysis of coastal geomorphology. This study has not gone in to such details.

For the remaining eight coastal districts, only areas that are below 5 metres above today’s mean sea level would be at risk from 1 m sea level rise. Based on these estimates, the total replacement value of infrastructure — port, power plants and major roads in Tamil Nadu — is calculated to be between Rs.47,418 and Rs.53,554 crores in 2010 terms.