Sea Level Changes Along Bangladesh Coast in Relation to the Southern Oscillation Phenomenon

• Published in: Marine geodesy Vol. 24; no. 1; pp. 65 - 72
• Main Authors: Khan, O. P. Singh Tariq Masood Ali, Murty, Tad S., Rahman, Md. Sazedur
• Format: Journal Article
• Language: English
• Published: 01.03.2001
• Subjects: Marine; ISW, Bangladesh
• ISSN: 0149-0419; 1521-060X
• DOI: 10.1080/01490410151079990

Interannual variations of sea level along the Bangladesh coast are quite pronounced and often dominate the long-term sea level trends that are taking place. The El Nino/Southern Oscillation (ENSO) induced variation is an important component of interannual mode of variations. The present article deals with the relationship between the sea level variations along the Bangladesh coast and the Southern Oscillation phenomenon. The mean tide level data of monsoon season (June to September) pertaining to Hiron Point (in Sundarbans) and Char Changa (on the mouth of Meghna River) have been analyzed and correlated to the Southern Oscillation Index (SOI). The annual variation of mean tide level in the coastal areas of Bangladesh reveals that the tide level reaches its peak during the monsoon season. The maximum tide level during the calendar year is recorded in August. Thus, it is not surprising that the inundation of the coastal belt of Bangladesh due to the floods is most common during the summer monsoon season, especially from July to September. Therefore, the sea level variations during the monsoon are of paramount importance to Bangladesh. The results of the present study show that both at Hiron Point and Char Changa there is a substantial difference between the mean tide level during the El Nino and La Nina monsoons. The mean tide level at Hiron Point is higher by about 5 cm during August of La Nina years as compared to that during the El Nino years. The difference at Char Changa, which is located at the mouth of Meghna River, is much higher. This is probably due to the increased fresh water discharge into the Meghna River during La Nina years. Thus at the time of crossing of a monsoon depression, the chances of widespread inundation are higher during a La Nin similar to a year as compared to that during an El Nino year. The Correlation Coefficients (CCs) between Mean Tide Levels (MTLs) at Hiron Point and Char Changa and the SOI during September (at the end of monsoon) are +0.33 and +0.39 respectively. These CCs are statistically significant at 90% and 95% levels, respectively. These results may find applications in the preparedness programs for combating sea level associated disasters in Bangladesh.