Co-occurrence probability of typhoon surges affecting multiple estuaries in the northern coastal region of Taiwan

Abstract Taiwan lies on the northwest Pacific and is usually invaded by typhoons in summers and autumns. When typhoons strike the coast, surges usually occur. In addition, if a typhoon surge occurs during a high-tide period, the water level starts to rise. As a result, largely urbanized and highly populated regions around the estuaries may be devastated by catastrophic damage owing to floodwater elevation rising and unable to drain off floodwater. Therefore, in order to allocate regional resources reasonably and prevent and reduce coastal disasters effectively, it is necessary to estimate the co-occurrence probability of typhoon surges in multiple estuaries. In this study, total 36 typhoon processes are applied to calculate the simultaneous-occurrence probability of typhoon surges in three estuaries in Nan-Kan River, Huang River, and Lan-Yang River in the northern part of Taiwan. We first use certain extreme-value distribution models to fit the simulated peak values of a typhoon surge. These univariate statistical distributions include the Pearson type III, Weibull, generalized extreme value, and lognormal distributions. Through hypothesis and goodness-of-fit tests, the Pearson type III distribution is chosen as the optimal curve to fit the typhoon surges in these three estuaries. Then, according to the dependence of the typhoon surges in these three estuaries, a three-dimensional compound probability distribution model P-GH-TriP3 is constructed, and the joint return periods are calculated. The results indicate the simultaneous-occurrence probability of disasters in these three estuaries is small, which can provide some reasonable proposal for coastal typhoon disaster prevention and reduction and ocean engineering design.