Sea Level Rise in the Southern Coast of Sri Lanka

Abstract

Sea level variation is short and long term fluctuation of water level by the forces of the location’s
astronomical, meteorological and hydrological properties. The volume of the ocean has been
increasing by absorption of additional heat accumulated in the atmosphere by natural and
anthropogenic activities during the last few decades. The high-frequency in-situ sea level observation
from Mirissa station and satellite altimetry data from ECMWE, AVISO were used for the analysis of
sea level dynamics from 1993 to 2021 in the southern coast of Sri Lanka. The Harmonic analysis tool
for MATLAB version was used to quantify tidal constituents and derivation of tidal pattern based on
form factor as presented Hicks in 2006. The resulted in tidal pattern is mixed semidiurnal (F=0.275,
Range: 0.25 to 1.5), which is included two high tides (50 cm) and two low tides (11 cm) per day with
different strengths within the micro-tidal category in the southern coast of Sri Lanka. The most
dominant tidal constitutes are semidiurnal lunar (M2) through 0.082 cph frequency with 95% of
significant level. The Power Spectral Density (PSD) of the tidal spectrum was captured two dominant
peaks related to M2 and S2. The satellite-derived monthly average sea level fluctuation shows a
significant seasonal signal with a range of 18-22 cm during the last 22 years on the southern coast of
Sri Lanka. The maximum seasonal sea level variation was recorded from December to January, while
the minimum from July to August. The peak month on the southern-coast is slightly later and lower
than the peak month on the east-coast. The seasonal variation of the Southern coast is comparable to
that of Sri Lanka’s west coast. During the last five years, the maximum extreme sea level height
recorded was less than 1 m. The long term sea level variation is a positive trend with approximately
3.12 mm per year in the Southern coast of Sri Lanka.

Keywords: Sea level, Seasonal, Sea level rise, Tide, Extreme height