A Study of Rainfall Changes and Thresholds of Extreme Rainfall Events in the Lienhuachih Area of Central Taiwan

蓮華池地區降雨變遷及極端降雨事件門檻值之研究

陸象豫(Shiang-Yue Lu) ； 孫銘源(Ming-Yuan Sun) ； 黃惠雪(Hui-Hsueh Huang)

《台灣林業科學》 33卷4期 (2018/12) Pp. 251-262

https://doi.org/10.7075/TJFS.201812_33(4).0001

摘要

Hydrological fluctuations tend to greatly vary, and rainfall characteristics have recently been significantly affected by influences of global warming worldwide. Rainfall changes and the occurrence of extreme events have received more attention because of their great impacts on ecosystem operations, agricultural activities, and design of hydraulic structures. Rainfall types, regimes, and long-term changes, and thresholds of extreme events were analyzed for the Lienhuachih area in this study using rainfall records from April 1928 to December 2016. Rainfall is unevenly distributed in the annual cycle with about 85.8% of amount and 68.8% of rainy days concentrated from April to September. Therefore, the wet season in the study area was defined as being from April to September rather than from May to October as in most other parts of Taiwan, owing to heavier spring rains. The Lienhuachih area has a mean annual rainfall of about 2409.0 mm and rainfall-days of about 144.6 d. An analysis of long-term rainfall changes showed a decreasing trend of about 28.0, 29.2, and 17.6 mm decade^(-1), for the annual total, and wet and dry seasons, respectively. Rainfall-days also showed a steadily decreasing trend of about 4.6, 2.3, and 2.4 d decade^(-1) for the annual total, and wet and dry seasons, respectively. Thresholds for extreme rainfall and drought were roughly 600 mm d^(-1) and 65 consecutive days of no rainfall, respectively, as estimated by quantities from the Extreme Value Type I frequency analysis of 50-yr return period. The decreasing trend for both rainfall amounts and rainfall-days and the more-frequent occurrence of extremely torrential rainfall indicate that rainfall will increasingly become temporally concentrated in the study area. This phenomenon may bring about greater difficulties for water resources management.

關鍵字

rainfall type ； long-term change ； threshold of extreme rainfall events ； Lienhuachih

並列摘要

近年來受到暖化的影響，世界各地水文事件的變動範圍日益擴大且降雨特性亦明顯的改變。由於降雨量雨分布的變化與極端降雨事件對生態系運作、農業活動和水利工程構設計有顯著的影響，因此格外受到關注。本報告藉由分析蓮華池地區1928年4月至2016年12月的降雨記錄，探討該地區的降雨型態、時間分布、長期變化趨勢以及極端降雨事件閾值。蓮華池地區年平均降雨量約2409.0 mm，降雨天數約為144.6天。由於在時間上分布相當不平均且春雨雨量較豐，致85.8％的年降雨量以及68.8%的年降雨日數集中於4至9月；因此該地區的濕季訂為4至9月，而非台灣其他多數地區的5至10月。長期的降雨變化分析顯示，蓮華池地區全年度、濕季及乾季降雨量均呈遞減趨勢，降幅每10年分別約為28.0、29.2與17.6 mm。降雨天數亦呈減少趨勢，全年度、濕季及乾季的降幅每10年分別約為4.6、2.3與2.4天。以極端值一型分佈函數經頻率分析所求得50年回歸週期日降雨量及連續無降雨天數，作為該地區極端降雨與極端乾旱的閾值，獲知該地區日降雨量需大於600 mm及連續65天無降雨方達到極端降雨與乾旱的門檻。降雨量和降雨日數的減少趨勢以及超大豪雨事件越趨頻繁，顯示蓮華池地區降雨在時間上分布日趨集中，此現象將使水資源經營管理日顯棘手。

並列關鍵字

降雨型態 ； 長期變遷 ； 極端降雨閾值 ； 蓮華池