## 5 Conclusions  
A process-based, three-dimensional, hydrodynamic and salinity-transporting, numerical model based on MIKE3, with a high-resolution of unstructured mesh and spatially varying bottom roughness, is applied to investigate the effects of the historical Typhoon Fongwong, which landed in Shanghai, on the hydrodynamics and saline water intrusion in the NB of the YRE. The model covers the entire YRE and the HB to present the complete typhoon track and to better express the hydrodynamics and saltwater exchange between the two estuaries. This numerical model is well validated quantitatively against tidal level, current velocity and salinity measurements. Three scenarios of Typhoon Fongwong, no wind force action and normal wind force were computed and analyzed to describe the influence of the typhoon on the NB of the YRE, and the main findings could be concluded as below. Although the tidal level process in the NB kept a semi-diurnal tidal type during Typhoon Fongwong, the tidal level had an increasing trend in the typhoon rising period, reaching the highest increase during the first half of the typhoon stable stage, then appearing as an obvious negative storm surge around 24 September 2014 due to the wind direction changing from S/SW to W/NW, the storm surge diminished in the typhoon falling stage and vanished at the end of the typhoon. In general, the tidal level and its range, and the tidal level difference caused by the typhoon, increased toward the upstream area in the NB due to the combined effects of the funnel-shaped plane geometry of the NB and the typhoon. The typhoon clearly increased the surface flooding velocity in the offshore area of the YRE due to a strong wind stress and low bottom roughness in deeper water. During a tidal cycle, the typhoon enhanced the flood current with a maximum increase by 0.13 m/s and weakened the ebb current with a maximum decrease by 0.12 m/s in the NB, and the typhoon changed the current more at the mouth than in the upstream area, due to both the typhoon becoming weaker after landing and increasing bottom roughness toward the upstream. The typhoon significantly increased the flood discharge and decreased the ebb discharge in the NB, i.e., the flood discharge increased by 29.38% and ebb discharge decreased by 84.01%, respectively. This led to a large change in the flow split ratio of the NB, that is, the flood flow split ratio increased from 3.31% to 4.51% with an increase ratio of 26.61%, while the ebb flow split ratio decreased from 0.99% to 0.54% with a decrease ratio of 83.33%. The surface salinity distributions during the typhoon's three periods had similar patterns, i.e., the high salinity in offshore areas and the salinity towards the upstream area both reduced, except for shoal areas with a high salinity. The effect of the typhoon on the salinity at the mouth of the river was much stronger than that at the upstream in the NB. The salinity at the mouth had a clear decrease around on 24 September 2014 due to the negative storm surge. A high surface salinity was maintained during the typhoon falling period, which indicated that the typhoon impact on salinity could last much longer than the tidal level and current. The typhoon changed the estuarine mixing type and enhanced water mixing and matter exchange in the vertical direction. The isohaline of 1 psu, 2 psu and 4 psu shifted upstream at 500 m, 1000 m and 19.5 km, respectively, in the NB due to Typhoon Fongwong. The salinity distribution gradually recovered to the normal salt wedge pattern in 3 days after the typhoon. [PERSON], [PERSON] and [PERSON] conceived and designed the framework of this study, analyzed and discussed the results, and wrote the paper; [PERSON], [PERSON] and [PERSON] conducted part of computations. All authors have read and agreed to the published version of the manuscript.