臺灣南部地區降雨量與降雨沖蝕指數時間與空間之變化

Temporal and Spatial Variations of Rainfall and Rainfall Erosivity in Southern Taiwan

屈峻廣(Chun-Kuang Chu)

指導教授 ： 李明熹

國立屏東科技大學/工學院/水土保持系所/碩士(2014年)

https://doi.org/10.6346/NPUST.2014.00280

摘要

近年來臺灣極端降雨事件發生頻繁，有累積雨量變高、降雨延時更長及區域性降雨強度增強等情況發生(陳晉琪等，2008)，對於土壤沖蝕的影響甚鉅。目前臺灣多以通用土壤流失公式(Universal Soil Loss Equation, USLE)進行土壤流失量之估算，其中降雨沖蝕指數(Rainfall Erosivity, R)直接反映在降雨對土壤沖蝕的影響程度。因此，本文為了解降雨特性的改變對降雨沖蝕指數之影響，以臺灣南部地區為例，蒐集境內76個中央氣象局雨量站的降雨資料，利用降雨沖蝕指數(R=E#westeur024#I30max)的計算方法，分析單場、月、季、乾濕季及年降雨量與降雨沖蝕指數的關係，探討臺灣南部地區降雨量與降雨沖蝕指數時間與空間的變化，有助於現今或未來對土壤沖蝕變化之了解。
研究結果顯示，在25,986場有效降雨事件中單場最大降雨量與降雨動能約有7成發生在莫拉克颱風侵臺期間。單場最大年降雨沖蝕指數範圍介於31,062~144,248 MJ-mm/ha-hr-yr。另外由降雨量與降雨沖蝕指數關係式中發現，降雨量與降雨沖蝕指數大多呈現高度相關。月的降雨量及降雨沖蝕指數主要集中在5~10月為主，約佔全年的9成，其中8月的月降雨量及降雨沖蝕指數最大，分別為566 mm及9,386 MJ-mm/ha-hr。季的降雨量與降雨沖蝕指數集中夏、秋兩季，佔全年9成以上。乾、濕季的降雨量與降雨沖蝕指數主要集中於濕季(5~10月)，佔全年約93%。年平均降雨量與降雨沖蝕指數範圍分別為1,000~6,401 mm及8,754~104,272 MJ-mm/ha-hr-yr，平均值為2,243 mm及32,080 MJ-mm/ha-hr-yr。熱帶地區各國的年平均降雨沖蝕指數多介於1,080~33,500 MJ-mm/ha-hr-yr，均比本研究區域低，顯示本研究區域受降雨所引發土壤沖蝕災害，較其他熱帶地區嚴重。
降雨量與降雨沖蝕指數時間變化結果顯示，在月、季及年的時間變化，大部份均呈現皆有逐年增加之趨勢。空間變化結果顯示，月、季、及年之平均的降雨量與降雨沖蝕指數，整體來看由西向東逐漸增加之趨勢，換句話說，由平原逐漸向山坡地遞增。在年平均降雨量、年平均降雨沖蝕指數與高程變化分析結果得知，當高程在1,000 m以下，兩者均隨著高程的增加而有急劇上升的趨勢，當高程超過1,000 m後，兩者則隨著高程的增加呈現緩慢下降的趨勢。

關鍵字

降雨沖蝕指數 ； 時間變化 ； 空間變化

並列摘要

In recently years, trend of the rainfall characteristics have gradually changed due to extremely heavy rainfall event in the world. Rainfall is the major cause of soil erosion dynamic factor. Rainfall erosivity is a numerical description of the potential of rainfall to erode soil and is one of the key input parameter for USLE modeling. 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 variations of rainfall and rainfall erosivity are investigated using a dataset monitored by 76 rainfall stations (from 1993 to 2012) in southern Taiwan.
There are 70% of all rainfall erosivity stations that the individual maximum rainfall amount and kinetic energy erosivity occurred during typhoon Morakot, 2009. We found that the rainfall and the rainfall erosivity have a strong positive relationship (R2> 0.7). The maximum annual rainfall erosivity varied from 31,062 to 144,248 MJ-mm/ha-hr-yr. Most of the average monthly rainfall and rainfall erosivity happened from May to October (above 90% of the yearly ones). The average maximum monthly rainfall was 566 mm on the June or August, and the average maximum monthly rainfall erosivity is 9,386 MJ-mm/ha-hr on the August. Most of the seasonal rainfall and rainfall erosivity happened in summer or fall (more than 90% of the yearly ones). More than 90% of the yearly rainfall and rainfall erosivity happened in the wet seasonal. The average yearly rainfall and rainfall erosivity are 2,243 mm and 32,080 MJ-mm/ha-hr-yr, respectively. The rainfall erosivity values in southern Taiwan are higher than other world’s ones. It shows that there is a serious rainfall erosion problem in the study area.
Result of temporal variation shows that the average monthly, seasonal and yearly rainfall and rainfall erosivity increase year by year. The spatial analysis shows the average yearly rainfall and rainfall erosivity increase from western region to eastern region and from plain to mountain region. The relationship of average yearly rainfall, rainfall erosivity and elevation show that the average yearly rainfall amount and rainfall erosivity abruptly increase as the elevation (< 1,000 m) increase, but they decrease as the elevation (> 1,000 m) increase.

並列關鍵字

Rainfall erosivity ； Temporal variation ； Spatial variation

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