考慮颱風與西南氣流相互作用對可能最大降水估算之影響

The Effect of Estimating Probable Maximum Precipitation by Considering Interaction Typhoon and Southwesterly Flow

劉正欽(Cheng-Chin Liu) ； 陳昭銘(Jau-Ming Chen) ； 楊道昌(Tao-Chang Yang) ； 林宥丞(Yu-Cheng Lin) ； 游保杉(Pao-Shan Yu)

《農業工程學報》 60卷4期 (2014/12) Pp. 34-47

https://doi.org/10.29974/JTAE.201412_60(4).0004

摘要

本研究主要提出西南氣流放大因子（Amplification Index of Southwesterly Flow, AISF）以代表考慮颱風與西南氣流影響下，對於可能最大降水（Probable Maximum Precipitation, PMP）之影響，研究區域為曾文水庫集水區。NCEP CFSR（The National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR)）題供日風速與日可降水的資料，而曾文水庫鄰近的阿里山測站提供了日降雨資料，資料年限為1979-2009年5-8月。透由上述資料，在台灣西南海面上找出阿里山降雨與NCEP CFSR平均風速與平均可降水有顯著相關之區域，再利用10場西南氣流事件，經由線性回歸及交叉驗證的方法估算西南氣流降雨回歸方程式。AISF主要研究3類颱風路徑之颱風事件，此3類颱風路徑對於研究區域有較顯著之影響。AISF的定義為歷史最大西南氣流回歸降雨量（PHMS）與特定颱風事件之西南氣流回歸降雨量（PST）之比值。而本研究總共選擇了17場颱風事件推估AISF。結果顯示在西南氣流的影響下，對於颱風降雨都有放大之作用（3類路徑之平均AISF皆大於1；1.18,1.07及1.17），並放大率符合颱風與西南氣流輻合之相對區域。最後將AISF應用於暴雨移置法，與曾文水庫建議之設計PMP比較，前者會較為保守，對於曾文水庫會有較佳之維護性，因此針對曾文水庫之設計PMP，需考慮西南氣流的影響，是有其必要性。

關鍵字

西南氣流放大因子 ； 西南氣流 ； 可能最大降水 ； 曾文水庫

並列摘要

The purpose of this study is to make a description of what effect the southwesterly flow has on Probable Maximum Precipitation (PMP) by proposing Amplification Index of Southwesterly Flow (AISF). The catchment of Tseng-Wen Reservoir is selected as the study area. NCEP CFSR provides the daily data including wind velocity and precipitable water. The Alishan raingauge, near the study area, provides local precipitation daily data. All data has selected from May to August, 1979 to 2009. The study finds that precipitation has significant relationship with average value of both wind velocity and precipitable water from NCEP CFSR (The National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR)) over the southwest ocean of Taiwan. Regression equation for predicting the southwesterly precipitation is deduced by applying linear regression method and cross validation method which using ten southwesterly flow events data. AISF is mainly proposed for researches on typhoon events among which the typhoons are formed along three typhoon routes which have a greater effect on the study area, and is defined as the ratio of historical maximum southwesterly flow precipitation (PHMS) to southwesterly flow precipitation (PST). The study chooses 17 typhoon events to estimate their respective AISF. The result shows that under the effect of southwesterly flow, there occurred strong typhoons and heavy rainfalls on a larger scale. The AISFs of all typhoons are all larger than 1 and also matches the usual occurrences for a convergence region of typhoon and southwesterly flow. Finally, AISF was applied on storm transposition method to compare with the design PMP of Tseng-Wen Reservoir. Finally, AISF was applied on storm transposition method to compare with the design PMP of Tseng-Wen Reservoir. The result shows it is necessary to consider the interaction of two weather systems (in this study: typhoon and southwesterly flow) on PMP estimated.

並列關鍵字

Amplification index of southwesterly flow ； Southwesterly flow ； Probable maximum precipitation ； Tseng-Wen Reservoir