Study of Rainfall Characteristics and Their Changes on the Hengchun Peninsula

恆春半島降雨特性及其變遷之研究

陸象豫(Shiang-Yue Lu)

《台灣林業科學》 31卷1期 (2016/03) Pp. 49-60

https://doi.org/10.7075/TJFS.201603_31(1).0004

摘要

本研究探討恆春半島降雨分佈、型態、變遷趨勢等特性，並進行頻率及設計降雨量分析。恆春半島降雨機制主要可分為鋒面雨、雷陣雨及颱風雨三大類，每一機制決定降雨型態及特性。該地區雨量在時間上的分佈極為不平均，約91.03%年雨量集中在5~10月(濕季)，其餘8.97%則分布於11月至翌年4月(乾季)。一年中平均約121.7天的降雨量超過0.1 mm，濕季的降雨天數約佔總降雨日數的71.41%，而乾季則佔28.59%。降雨量過度集中於濕季，但降雨天數則否，顯示濕季的降雨強度通常較大且較集中。年降雨量及濕季的降雨量在過去40年間，均有顯著增加的現象，然而乾季的降雨量卻以每十年2.5mm的微幅減少；全年降雨量約以每十年14.6 mm的幅度增加，濕季降雨量每十年則增加12.8 mm。證實恆春地區降雨量有增加的趨勢，但增加的雨量多集中於濕季。降雨日數長期變化呈現穩定減少的趨勢，減少的幅度在1990年後更為明顯。全年降雨日數減少的幅度最大，乾季的降雨天數減少幅度則較緩，而一年中日降雨量超過30 mm的天數，無論乾濕季均顯示有增加的趨勢。此外，本報告亦以極端值第一型分佈法進行頻率分析，求得2、5、10、25、50及100年回歸週期之10分鐘、1、6及24小時延時之降雨量；亦由歷年降雨紀錄，求得3、6及12小時延時的設計降雨歷線。期望這些研究結果，可做為恆春地區水利工程構造物及防洪工程設計之參考。

關鍵字

降雨特性 ； 恆春半島 ； 長期變遷 ； 設計降雨

並列摘要

Rainfall characteristics including types, regimes, frequency behaviors, long-term changes, and design storm distributions were analyzed for the area of the Hengchun Peninsula in this study. The mechanism of rainfall in the study area can mainly be classified as frontal rain, thunderstorms, and typhoon rain. Each of these mechanisms dominates the type and characteristics of rainfall. Rainfall is extremely unevenly distributed in the annual cycle. About 91.03% of the rainfall is concentrated in the period from May to October (wet season), and the rest (8.97%) is in the period from November to April (dry season). There was a total of 121.7 days on average which had at least 0.1 mm d^(-1) rainfall in the yearly cycle of the study area. The percentage of rainy days in the wet season of the total rainy days in a year was 71.41%, and that of the dry season was 28.59%. This phenomenon indicates that rainfall in the wet season is relatively strong when it occurs, and that in the dry season is usually in smaller amounts. Annual and wet season rainfall totals have significantly increased in the last 4 decades. Annual rainfall has increased about 14.6 mm decades^(-1) and that in the wet season has increased about 12.8 mm decades^(-1). However, the rainfall amount in the dry season has slightly decreased at a rate of -2.5 mm decades^(-1). This phenomenon indicates that there is an increasing trend of rainfall, but the increase is mainly in the wet season. Long-term changes of rainfall-days show a steadily decreasing tendency. Rainfall-days were obviously reduced after 1990. Annual rainfall-days showed the largest declining rate, while rainy days in the dry season showed the least decline. The number of days with a rainfall amount exceeding 30 mm showed an increasing tendency in both the wet and dry seasons. In addition, the Extreme Value Type I distribution was used in this study to estimate magnitudes of 2-, 5-, 10-, 25-, 50-, and 100-year return intervals for 10-min, 1-h, 6-h and 24-h rainfall events. Design storm distributions for 3, 6, and 12 hours were also been analyzed. Results of the design storm analysis combined with those of the frequency analysis can provide a reference for designing hydraulic structures and water control works on the Hengchun Peninsula.

並列關鍵字

rainfall characteristics ； Hengchun Peninsula ； long-term changes ； design storm