Coastal Currents and their Extremes in Singapore

COASTAL CURRENTS AND THEIR EXTREMES IN SINGAPORE

Jun Yu Puah*¹, David Lallemant^1,2, Ivan D. Haigh³, Kyle M. Morgan^1,2, Dongju Peng², Adam D. Switzer^1,2

¹Asian School of the Environment, Nanyang Technological University, Singapore

²Earth Observatory of Singapore, Nanyang Technological University, Singapore 

³School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, UK

*a210012@e.ntu.edu.sg

 

Extreme currents are integral as they affect ship navigation and public safety. However, research on extreme currents is scarce and further hampered by the lack of long-term observational records. In this study we estimate the characteristics of extreme shallow-water currents in Pulau Hantu and Kusu Island located in the Singapore Strait and investigate their potential drivers. We apply harmonic analysis to around 12 months of data to decompose the observed currents into tidal and residual components. The tail distribution of the residual component was estimated using extreme value analysis by fitting a non-homogeneous Poisson process to the data, accounting for temporal and directional dependences. Random simulations of tidal currents were then combined with residual currents via the Joint Probability Method to generate new observed current realizations. Finally, wind data was extracted from ERA5 Reanalysis to investigate how well monsoonal winds correlates with residual currents across monsoon periods. Tidal variance ranges from 29-69% across all sites, which is lower than expected given the dominance of tidal currents in the Singapore Strait. Extreme currents orient mainly in 2 directions along the coastline contours. Mean speed in Pulau Hantu is greater than Kusu Island and may be attributed to the hydrodynamic pressure gradient set up by the monsoons. Lastly, the stronger correlation observed in some sites during the inter-monsoon periods demonstrates the importance of localized winds from local systems such as Sumatra squalls in driving extreme currents. The variability of the study results highlights the challenges in modelling currents in the Singapore Strait given its complex bathymetry, equatorial weather patterns and complex tidal regime. Future work could include the integration of shipborne Automated Information Systems to examine extreme currents and evaluate the role of meteorological effects in driving extreme currents in the region.