Response of storm surge and M2 tide to typhoon speeds along coastal Zhejiang Province

Storm surges are among the most devastating natural hazards occurring in coastal regions of Zhejiang Province. A nested tidal model is built to simulate the storm surge generated by typhoons with varied velocities. Two typhoons with extreme moving speeds (Mary and Kai-tak, with low and high moving speeds, respectively) between 1949 and 2020 are simulated and analyzed. To investigate the changes of storm surge and the influence of M2 tide caused by the moving speed, three different moving speeds (2.0, 1.0 and 0.5 times) are studied based on Chan-hom. The results show that: The landing intensity of the low moving speed typhoon is weaker than that of the high moving speed typhoon, but the former has a longer-lasting impact on the storm surge. When the moving speed is slower, the wind points towards the shore for a longer time, which increases the average water level in the area from the west of the Zhoushan sea area to the Qiantang River. With the decrease of typhoon moving speed, the amplitude of the tide decreases, while the change of lag angle varies in different water areas.