異常波浪的發生對於航行與海域遊憩安全都造成很大的威脅，異常波浪的預測可以提供預警訊息，降低危害風險。截至目前為止，異常波浪發生機制仍未有定論，以定率的方式進行預測尚不可行，本研究以序率方法從事異常波浪發生機率研究。本研究基於非線性波理論，推導異常波浪發生機率估算之理論式，結果顯示異常波浪的發生機率與水位變化的峰度以及波浪數目有關，數值解顯示非線性理論推估所得之異常波浪發生機率最大為線性波理論所得之4倍。本文以基隆碧砂漁港外長期連續波浪觀測資料進行理論驗證，分析結果顯示異常波浪發生機率平均有22.4%的誤差，本文檢討其原因認為與在推導最大波高超越機率時之近似以及使用線性理論之波高與水位均方根比值是可能的誤差來源，本文研究發現，前者的影響程度很小，後者為主要之誤差來源，經以實測波高與水位均方根關係式代入推導異常波浪發生機率，並再以長期實測數據驗證，均方根誤差降低至15.8%，改進了異常波浪發生機率之估算。

Freak wave will cause huge risks to ships or people doing costal activities. Prediction of freak wave can provide information for early warning and then decrease risk of hazards. Since the mechanism of freak wave is still unclear so far, deterministic prediction is not possible. Therefore stochastic method is used by this study for research of occurrence probability prediction of freak wave. In this study, nonlinear wave theory is applied for formula to estimate freak wave occurrence probability. Result demonstrates that occurrence probability of freak wave is related to two parameters: number of waves and kurtosis of water elevation.
Analysis of the formula shows the maximum occurrence probability can become four times larger than the probability estimared under linear condition. Moreover, validated by the continuous measured data at Bisa Harbor, the average root-mean-square-error of assessment of occurrence probability is 22.4%. The possible reason to this difference is the ratio of significant wave height and root-mean-square of water elevation, which is assumed to be 4 under linear condition. Modified the formula by our field measurement data, the accuracy of estimation of occurrence probability improved. The modified formula is also validated by other in-situ data and can be used for future works with better assessments.

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