Rise in sea levels along the Indian coasts: Sea water levels go up by 1.30 mm per year on average

By Syed Akbar
Hyderabad, July 28: Visakhapatnam, Mumbai, Kochi and Chennai are facing long term threat of sea invasion as the average sea level in these cities has been going up by 1.30 mm per year.
Data collected by the city-based Indian National Centre for Ocean Information Services shows that the trend of mean sea level rise varies from 1.06 mm to 1.75 mm per year in the Indian Ocean that includes the Arabian Sea and the Bay of Bengal. Analysis of data of 113 years in case of Mumbai reveals that the increase in mean sea level is 1.20 mm per year while data for 54 years in Kochi shows an increase by 1.75 mm per year.
In Visakhapatnam historic data for 53 years shows a net sea level rise by 1.09 mm per year. Diamond Harbour (Kolkata), which has data for 55 years, shows an average increase in sea level by 5.74, the highest for any sea-side city in the Indian Ocean. The rise has been attributed to increase in sea surface temperatures. The annual mean sea surface temperature has risen by 0.31 degrees C, 0.40 degrees C and 0.24 degrees C per decade in Mumbai, Kochi and Visakhapatnam respectively.
According to Incois officials, the increase in sea levels pose severe threat to the life and economy of the East and West coasts as 26 per cent of the country's population live within 50 km from the shoreline. Most of the coastal areas are low lying and vulnerable to oceanogenic hazards like tsunamis and storm surges, besides sea level rise.
Incois, which has now emerged as a major tsunami research and prediction hub in the Indian Ocean rim, monitors the levels in the sea through its active Argo floats deployed at dozens of locations. It also banks on satellite data of earth's gravity field.
Besides rise in mean sea level, there has also been an increase in the annual mean tidal level in Kochi, Visakhapatnam and Mumbai. Kochi registers the highest trend of 1.3 mm/year, followed by Visakhapatnam (0.97 mm/year) and Mumbai (0.8 mm/year). The mean tidal level trend values were worked out on the basis of data available since 1878 in case of Mumbai, 1939 in Kochi and since 1937 in case of Visakhapatnam.
According to official records, among the seasonal trends, the highest trend of 1.8 mm/year has been found at Kochi during the pre-monsoon season. The fluctuations in sea level from one season to other is the lowest at Mumbai and highest at Visakhapatnam. The annual mean sea level has a rising tendency at Mumbai, Kochi and Visakhapatnam with Kochi registering the maximum rising trend of 1.3 mm/year.
Incois officials warn that increase in sea levels will lead to loss of habitat land and bio-diversity, ground water and soil contamination, and damage to important ecosystems including sea-grass, mangroves and coral reefs. Sea-level rise disturbs the food cycle and redistribution of energy, thus causing economic loss to coastal zones.