Amplification of regional tides in response to sea level

Abstract

The study investigates the temporal change in tides under the background of rapid sea level rise, for a highly vulnerable coastal region. It highlights the existence of non-astronomic tidal variability at seasonal and secular time-scales in the Ganga-Brahmaputra-Meghna (GBM) delta, along with increasing low and high tidal levels. The observed variability in semi-diurnal tides was found to be coherent to the mean sea level changes. M2 tide can be a proxy for sea level changes as they show a direct relationship. Steric changes were introduced in the barotropic ADCIRC (ADvanced CIRCulation) model and the results proved that change in water depth modulates the energetics of the tidal wave thereby causing amplification. A regionally varying tidal response was noticed, such that the regions associated with the GBM delta showed maximum amplification. The factors that can cause tidal amplification are region-dependent and coastal geomorphology plays an important role in it. Tidal prediction based on changing sea level was able to capture the observed seasonal modulation of tides and increasing trend in low and high tidal levels. Incorporating the effect of changing tides can improve the accuracy of tidal predictions and will help advance studies regarding regional sea level change, coastal flooding and tide-surge interaction.