Evaluation of sea level rise and associated responses in Hangzhou Bay from 1978 to 2017

The mean sea level, extreme sea level, and astronomical tide in Hangzhou Bay were analyzed using the tide gage data from 1978 to 2017 in Tanxu station, and the effects of rising sea levels on floods were estimated. The mean sea level in Hangzhou Bay showed a significant rising trend of 4.6 mm per year in 1978–2017. This rate was much higher than the mean sea level of the China seas, and the extreme sea level in Hangzhou Bay increased at the rate of 0.011 m per year. During 1978–2017, the mean tide range increased at the rate of 1.30 cm per year. The amplitude of M2 significantly increased at the rate of 0.57 cm per year, whereas the phase lag decreased at the rate of −0.21° per year. The amplitude and phase lag of the K1 tidal component slightly decreased at the rate of −0.03 cm per year and −0.07° per year, respectively. The changes in extreme sea level in Hangzhou Bay were mainly caused by variations in mean sea level. The coastal areas of Hangzhou Bay at risk from flooding due to the 100-year sea level return will increase by about 400 km2 by 2050. Keywords: Hangzhou Bay, Sea level rise, Astronomical tide, Extreme sea level, Marine disaste