近年來因極端降雨事件發生頻繁,造成臺灣降雨特性發生變化,如累積雨量變高、降雨延時加長及區域性降雨強度增加等情形(陳晉琪等,2008)。降雨沖蝕指數是通用土壤流失公式(Universal Soil Loss Equation, USLE)重要的參數之一,它的大小表示降雨對土壤沖蝕能力的高低,分析降雨沖蝕指數的變化有助於瞭解降雨對土壤沖蝕的影響及變遷。臺灣東部地區(宜蘭縣、花蓮縣、臺東縣)受到東北季風與颱風的直接影響,其降雨特性會異於西部地區,且近年來相關之降雨沖蝕指數研究較少。因此,本文蒐集境內51個中央氣象局雨量站2002~2012年10分鐘等間距雨量資料,分析單場、月、季(乾、濕)及年降雨量與降雨沖蝕指數的關係及迴歸關係式,進而探討臺灣東部地區降雨沖蝕指數時間與空間的變化。 本文由19,106場的有效降雨事件分析結果顯示,最大年降雨沖蝕指數介於12,217~173,529 MJ mm ha-1 hr-1 yr-1,降雨沖蝕指數及降雨量迴歸關係式皆達到高度相關以上,顯示兩者關係密切,因此本文建立東部地區51個雨量站各站之迴歸關係式。時間變化分析發現,月、季及年之平均的降雨量及降雨沖蝕指數大部分皆呈上升的趨勢。空間變化分析顯示,月、季及年之平均的降雨量及降雨沖蝕指數,大致由平原向山區逐漸增加,且受緯度影響由南向北(由臺東向宜蘭)增加。另外發現研究區域除了受颱風影響外,常會伴隨東北季風產生共伴效應,造成高強度降雨,對降雨沖蝕指數影響甚鉅。本文研究結果,可提供沉砂設施規劃之參考依據,提高工程設計效益。
In recently years, frequency of high intensity rainfall, long rainfall duration and heavy rainfall are found to increase in Taiwan (Chen, 2008). Rainfall erosivity index R is a key input parameter to the USLE. R describes the soil loss potential caused by precipitation, which can be understood to change in correspondence to changes in extreme rainfall events. R is calculated from the total kinetic energy and the maximum 30-min rainfall intensity of a storm. Therefore, a lack of short duration rainfall intensity data in some countries makes applying the rainfall erosivity index more difficult. For those areas without the data and resources required to calculate rainfall erosivity index, an alternative approach has typically been used to estimate rainfall erosivity index. The purpose of the present study is estimating the rainfall erosivity based on event, monthly, seasonal, dry and wet seasonal and annual precipitation data, respectively. Temporal and spatial of rainfall and rainfall erosivity variations are investigated using 19,106 effective rainfall events by 51 rainfall stations of the Central Weather Bureau (from 1993 to 2012) in eastern Taiwan (Yilan, Hualien, Taitung). The result shows that maximum annual rainfall erosivity varied from 12,217 to 173,529 MJ-mm/ha-hr-yr. Rainfall and rainfall erosivity have a strong positive relationship. Temporal variation of rainfall erosivity shows that the average monthly, seasonal and yearly rainfall and rainfall erosivity increase year by year. The spatial analysis shows average annual rainfall erosivity increases from plain to mountain region, and from southern to northern (from Taitung to Yilan). Average annual rainfall erosivity is highly related with the latitude. In addition, rainfall erosivity index is affected by the typhoon and the northeast monsoon in eastern Taiwan.