Tides and longer-term modulation of sea level around Malaysian coastal seas

Tides are one of the primary contributors to coastal sea level variability. Previous research overlooked the contribution of tidal modulation to interannual sea level variability, especially during extreme events. In this study, the characteristics and longer-term modulation of tides in the Malaysian coastal sea are determined. We analyse the observed historical data for 18 tide gauges and 100 years of predicted TPXO 7.2 model tide data along the coast to determine the tidal components and long-term tide modulation effects at each station. Malaysia has four distinct regions where tides differ: (1) In the Strait of Malacca (MS), Celebes Sea (CS), and Sulu Sea (SS), semidiurnal and mixed semidiurnal tides prevail; (2) In South China Sea (SCS), diurnal and mixed diurnal tides dominate; (3) In Central MS has the highest M2 and S2 component tide amplitudes with 1.38m and 0.58m, respectively; and, (4) At SCS, tide stations indicated a significant diurnal amplitude (S1 and O1). At SCS peninsular Malaysia, there is strong seasonal variability due to monsoon effects. In the SCS (diurnal tides), long-term modulation for the 18.6 nodal cycle dominated with maximum values ranging from 0.15m to 0.25m. Lunar perigee, the 4.4-year with a range of 0.1-0.15m dominated the MS, SS, and CS (semidiurnal tides). Understanding the characteristics of tides and quantifying their amplitude is crucial for developing effective coastal management strategies and mitigating the effects of coastal flooding and extreme events.