长江口极端增水非平稳变化特征研究

Study on the non-stationary characteristics of extreme storm surges along the Changjiang River Estuary

本文基于ADCIRC构建适用于长江口的台风暴潮模型,对1979–2019年间长江口台风增水过程进行数值重构;结合非平稳广义极值分布和状态空间模型,构建适用于刻画长江口极端增水非平稳变化的频率统计模型,研判非平稳变化引起的极端增水量值调整情况。结果表明,长江口各验潮站处极端增水的非平稳广义极值分布时变位置参数在2008年前表现为波动特征,2008年后呈现逐渐增大趋势。2008–2019年间各验潮站处极端增水时变位置参数的线性上升率介于0.8~1.2 cm/a之间。基于上述变化趋势,考虑极端增水非平稳变化时长江口各验潮站处百年一遇增水均大于基于平稳假定的推算结果,二者差值介于8~15 cm之间。经分析,2008年后北上到长江口附近海域再转向外海的热带气旋强度有明显增强趋势,致使长江口各验潮站处年第二和第三大值增水增大,这是导致各验潮站处风暴增水极值分布位置参数出现趋势性增大的主要原因。

Under the background of global climate change,the extreme storm surge events caused by tropical cyc-lones in the Changjiang River Estuary and adjacent coastal area present non-stationary feature.In this study,a storm surge model for the Changjiang River Estuary was constructed using the ADCIRC model to reproduce the storm surges during 241 tropical cyclones affecting the Changjiang River Estuary from 1979 to 2019.By combin-ing the non-stationary generalized extreme value distribution with the state space approach,a statistical model for capturing the non-stationarity of extreme storm surges was built to investigate the spatiotemporal variability of the extreme storm surges in the Changjiang River Estuary and its adjacent coastal area.The statistical model can well reproduce the non-stationary feature of extreme storm surges,which was mainly represented by the time-dependent location parameter.The time-dependent location parameters at the tidal gauge stations were stationary before 2008 and presented increasing trends afterwards,which was mainly caused by the increase of the annual second-and third-largest storm surges.The reoccurrence period of storm surge event with 100-year return period under the sta-tionary assumption was reduced to around 40–80 years,indicating an increased flood risk in the Changjiang River Estuary.Combined with the changes in the intensity and path of the tropical cyclones that caused the annual second-and third-largest storm surges,it was concluded that the increasing trends of extreme storm surges were mainly caused by the increase in the intensity of the tropical cyclone that tracking northward to the offshore of the Changjiang River Estuary and veering eastwards.