台灣山地與平地之降雨時空變異研究

Abstract

在全球氣候變遷的情境下，降雨的變異受到許多學者關注，然而山地區域缺乏相關研究；本文旨在研究臺灣地區山地與平地之降雨量、日降雨強度、降雨日數等特性分佈的空間與時間變異，再應用本研究所得結果之季節趨勢，揉合時間序列分析與ARIMA模型進行各站台季節與逐月資料之一般模型建構與預測，並探討未來降雨情境對水文循環之影響。為此，本研究透過1978年至2008年間台灣120個水利署雨量站之年度與季節時序資料進行降雨量(Pr)、平均日降雨強度(η)、降雨日數比例(λ)之相關分析，並對於各項降雨特性的長期趨勢進行研究。本研究依參考文獻以海拔1000 m區分山地與平地區域，總體而言，山地區域的雨量與降雨日數均高於平地，而山地雨量之空間分佈主要由日降雨強度決定，平地區域雨量之空間分佈則由降雨日數與日降雨強度共同決定。年間降雨量的變異分析結果顯示，大多數站台不論在年度或季節方面，降雨量年間變化與日降雨強度年間變化具有較降雨日數為大的相關性，因此，降雨量在山地與平地的空間分佈所仰賴之降雨特性是不同的，在山地仰賴日降雨強度，而平地仰賴日降雨強度以及降雨日數。年度與季節等二種時間尺度下的長期趨勢分析顯示，趨勢顯著之站台佔全體站數之比例不高，其空間上之分佈亦不均一，因此，本研究推論降雨量之變化趨勢並非總體的現象，年雨量的長期趨勢與日降雨強度變化的長期趨勢呈顯著相關，具有顯著長期趨勢之站台主要分佈於中央山脈以西，而山地與平地的顯著站台比例相近；季節雨量的長期趨勢與日降雨強度變化的長期趨勢呈顯著相關，季節降雨量趨勢顯著之站台多位於平地部份，趨勢顯著之站台分佈亦不均一，因此，季節尺度下的長期降雨趨勢亦非總體的現象。

Variations in rainfall characteristics have been received a lot of attention in lowland areas while they were not clear in mountainous areas. This research first was to explore spatial and temporal variation of rainfall characteristics in the mountainous and lowland areas in Taiwan. As well, this research forecasted time series using ARIMA models, and then discussed possible impacts on hydrological cycles. To these aims, rainfall amount (Pr), daily rainfall intensity (η), and ratio of rain days (λ) between 1978 and 2008 from 120 stations in Taiwan were presented including annual spatial variation, temporal variations, and marginal long-term trend. In both of annual and seasonal time-scale analysis, spatial variation in Pr was highly explained by η at mountainous stations and by both η and λ at lowland stations, regardless of annual or seasonal datasets. The temporal variation of Pr was determined from η than λ at each station, this was consistent with mountainous and lowland areas. Long-term analysis showed that significantly increases in Pr were not distributed evenly in Taiwan and the changes were not a general phenomenon for the low ratio of total stations. Stations with changing rainfall characteristics located in the west of the central mountain range rather than the east. Further, in annual analysis, the ratio of these changing stations in the mountainous areas was almost same as those in the lowland areas. While I had found different spatial pattern of the long-term trend of Pr, η and λ in each season. Even so, long-term changes of rainfall were still uncommon phenomenon in Taiwan.