长江口徐六泾水文站极值水位研究

Extreme water level at Xuliujing hydrological station in the Yangtze Estuary

在气候变化背景下,极端天气和水位事件频发。为了分析长江口极端潮位的长周期特征,研究基于极值理论相关方法,采用近33 a实测资料对长江口极值潮位趋势性和重现期进行分析,结果表明:长江口徐六泾站年极值水位呈轻微下降趋势,直接原因是大通流量减少导致当地年均海面的下降;区分组模型结果显示,台风“温妮”期间长江口造成的风暴潮位为100 a一遇,而POT模型计算结果仅为60 a一遇,100 a一遇重现期潮位约7.0 m;潮位重现期的计算本质是一种用频率代替概率、从样本推求整体的过程,具有一定不确定性。其意义在于以可获取的数据为基础,计算事件发生的风险率,旨在为工程设计或风险管理提供依据。

In the context of climate change,extreme weather and water level events occur frequently.To study the long-term evolution characteristics of extreme tide levels in the Yangtze Estuary,this paper analyzes the tendency and the return period of the extreme tide level in the Yangtze Estuary based on the methods of the extreme value theory,using the observed data in the last 33 years.The results show that the annual extreme water level at Xuliujing station shows a slight downward trend,which is directly caused by the decrease of local mean sea level due to the reduced river discharge of Datong station.The storm tide level caused by Typhoon Winnie in the Yangtze Estuary is estimated to be a once-in-a-century event according to the Block Maximum model.However,it is projected to occur once in 60 years based on the results of the POT model,with the once-in-a-century return period tide level reaching 7.0 m.Calculation of the return period of tide level is essentially a process of replacing probability with frequency and extrapolating from sample to the whole,with a certain degree of uncertainty.Its significance lies in using obtainable data to calculate the risk rate of an event,providing a basis for engineering design or risk management.