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 threatof sea invasion as the average sea level in these cities has been going up by 1.30 mm peryear. Data collected by the city-based Indian National Centre for Ocean Information Servicesshows that the trend of mean sea level rise varies from 1.06 mm to 1.75 mm per year inthe Indian Ocean that includes the Arabian Sea and the Bay of Bengal. Analysis of data of113 years in case of Mumbai reveals that the increase in mean sea level is 1.20 mm peryear 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 peryear. Diamond Harbour (Kolkata), which has data for 55 years, shows an average increasein sea level by 5.74, the highest for any sea-side city in the Indian Ocean. The rise hasbeen attributed to increase in sea surface temperatures. The annual mean sea surfacetemperature has risen by 0.31 degrees C, 0.40 degrees C and 0.24 degrees C per decade inMumbai, Kochi and Visakhapatnam respectively. According to Incois officials, the increase in sea levels pose severe threat to the lifeand economy of the East and West coasts as 26 per cent of the country's population livewithin 50 km from the shoreline. Most of the coastal areas are low lying and vulnerableto 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 theIndian Ocean rim, monitors the levels in the sea through its active Argo floats deployedat 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 tidallevel in Kochi, Visakhapatnam and Mumbai. Kochi registers the highest trend of 1.3mm/year, followed by Visakhapatnam (0.97 mm/year) and Mumbai (0.8 mm/year). The meantidal level trend values were worked out on the basis of data available since 1878 incase of Mumbai, 1939 in Kochi and since 1937 in case of Visakhapatnam. According to official records, among the seasonal trends, the highest trend of 1.8mm/year has been found at Kochi during the pre-monsoon season. The fluctuations in sealevel from one season to other is the lowest at Mumbai and highest at Visakhapatnam. Theannual mean sea level has a rising tendency at Mumbai, Kochi and Visakhapatnam with Kochiregistering the maximum rising trend of 1.3 mm/year. Incois officials warn that increase in sea levels will lead to loss of habitat land andbio-diversity, ground water and soil contamination, and damage to important ecosystemsincluding sea-grass, mangroves and coral reefs. Sea-level rise disturbs the food cycleand redistribution of energy, thus causing economic loss to coastal zones.