## 5 Conclusions  
In 2015, five typhoons affected the area of the Taiwan Strait, four of which were super typhoons. This study focused on the response of the waters of the Taiwan Strait to the passage of typhoons Soudelor (2015) and Dujuan (2015), which were the two strongest typhoons to affect the Taiwan Strait area in 2015. Both Soudelor and Dujuan made landfall twice and caused severe damage in China. We analyzed observations from buoys and tide stations acquired during the passage of the two typhoons, as well as the results of numerical modeling simulations.  
Analysis revealed that prominent resonant coupling between the astronomical tide and the storm surge resulted in a tidal period oscillation on the storm surge and reduced tidal range. The high tide arrived early because the tide wave was accelerated by the rise of the water level attributable to the storm surge. It confirms that tide-surge interaction is inevitable in coastal areas with shallow water depth and large tides. The predicted water level matched the observations well, especially the predictions that considered tide-surge interaction.  
Wave observations and modeling results showed that wave height oscillated within the tidal period. Waves are affected by both currents and water level. Wave heights are modulated along a tidal cycle because of tide-induced water level variations shift the cross-shore position of the surf zone. In coastal zones subjected to strong tidal currents such as tidal inlets, tidal currents can substantially affect the wave field. Tidal current flattens the wave amplitude and reduces the wave height. However, during this ebb phase, as and when currents increase, the wave steepness increases with the increase in wave height together with the decrease in wavelength. This study found that waves in the middle of the Taiwan Strait were affected primarily by the current, whereas water level had the greatest effect when the water level was comparable with the water depth in coastal area.  
Figure 17: Water depth on the western bank of the Taiwan Strait.  
Wave setup, which is the water level rise driven by typhoon waves, was also simulated for the passage of typhoons Soudelor and Dujuan. The wave setup was enhanced as the typhoons approached and reached its highest value when the typhoons made landfall. It was found that wave setup also oscillated within the tidal period. The wave setup, which was found to be positive (negative) in the nearshore (offshore) area, was over 15 (-8) cm in this study. According to the simulation results, local terrain is the most important influencing factor of wave setup distribution.  
Conceptualization, S.S. and L.Z.; Methodology, L.Z.; Software, L.Z.; Validation, L.Z. and F.Z.; Formal Analysis, S.S.; Investigation, L.Z.; Resources, Y.X. and S.S.; Data Curation, Y.X.; Writing--Original Draft Preparation, L.Z. and F.Z.; Writing--Review & Editing, S.S., F.Z., and Y.X.; Visualization, L.Z. and F.Z.; Supervision, S.S.; Project Administration, S.S. and Y.X.; Funding Acquisition, S.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Key R&D Program of China grant number No. 2017 YFC1404804 and 2016 YFC1401104 and Marine Economic Development Subsidy Project of Fujian, China grant number No. ZTHY-2019-2.  
The authors declare no conflict of interest.