## 3 Results and Discussion  
The tide calculation results are verified, as shown in Figure 3; 91.7% of the astronomical tide level errors were within 20 cm. The current velocity and direction verification results are shown in Figure 4. The calculated value of the vertical average current velocity was basically consistent with the measured value, and the simulation of the flow direction was also more consistent with the actual measurement, indicating that the astronomical tide model simulation accuracy is satisfactory and can be used as the basis for further storm surge simulation. Figure 4: Verification of current velocity and angle during spring tide (**a**) velocity (**b**) angle. Figure 3: Verification of astronomical tide at a temporary tide station. In this study, we employed data from Typhoon In-fa (2021) for model validation, sourced from NOAA. Typhoon In-fa, which formed in July 2021, emerged from a tropical disturbance in the western Pacific Ocean and rapidly intensified into a Category 4 typhoon. As shown in Figure 5, its large wind field and well-defined eye posed threats to the East China Sea, with sustained winds exceeding 25 m/s. The verification results are shown in Figures 6 and 7. Firstly, sea level pressure, wind speed 10 m from the surface, wind direction from ERA5 reanalysis data, and the ground and high-altitude elements were extracted (the wind speed was calculated from the zonal and meridional wind speed), which were compared with the Fujita-Takahashi parameterized wind field model. The two models were substituted into the Delft3D-Flow module for calculation so as to obtain the storm surge verification model of Qushan station (122\({}^{\circ}\)17.17\({}^{\prime}\) E, 30\({}^{\circ}\)26.35\({}^{\prime}\) N) and Sijiao station (122\({}^{\circ}\)30.82\({}^{\prime}\) E, 30\({}^{\circ}\)43.23\({}^{\prime}\) N). Figure 5: Typhoon In-fa (2021) data. (Fink line represents the typhoon path, and the number represents the date of July 2021). Figure 6: Comparison between simulation and measured data of Qushan station (**a**) ERA5 model (**b**) Fujita–Takahashi model. This paper applied bias degree (Bias) and root mean square error (RMSE) to determine the accuracy of the typhoon storm surge model. Bias represents the difference between the calculated value and the measured value:  
\[\text{Bias}=\frac{\Sigma(Q_{c_{i}}-Q_{m_{i}})}{\Sigma Q_{m_{i}}} \tag{9}\]  
in which \(Q_{m_{i}}\) is the measured data of the \(i\) th one; \(Q_{c_{i}}\) is the calculated data of the \(i\) th one; M is the total number of values. If Bias is near zero, it indicates that the error between the calculated and measured values of the results is low. The RMSE represents the distribution of data points around the best-fit line. For a perfect match between calculated and measured values, the root mean square error is zero. The RMSE is obtained by the following relation:  
\[\text{RMSE}=\sqrt{\frac{\Sigma\left(Q_{c_{i}}-Q_{m_{i}}\right)^{2}}{M}} \tag{10}\]  
The evaluation criteria presented in Table 1 reveal that the Fujita-Takahashi model demonstrates higher accuracy during the typhoon migration phase, while the ERA5 model exhibits superior precision in the post-typhoon landfall period. By comparing the parameterized wind field model and ERA-5 in our analysis, we identified significant differences between the two before and after typhoon landfall. The morphology of the typhoon underwent drastic changes before and after landfall, deviating from its previously assumed symmetrical circular shape, as depicted in the parameterized typhoon field formula ([PERSON], 1952) [20]. Consequently, the formula for the typhoon field was theoretically not applicable after landfall, which indirectly corroborates our findings that the postlandfall typhoon field model exhibited poorer performance in calculating water levels. Drawing upon the validated structure outlined above, we present a novel approach for investigating typhoon storm surges.