基流是河川中重要的組成部份之一，不僅是地下水系統中維持河川乾季流量的主要來源，也是提供生態環境與人為活動中用水的重要水資源。近年來由於氣候變遷的影響，臺灣的乾季時期延長，濕季時期延後，導致降雨日數的減少以及降雨強度的增加，加上降雨空間分佈不均以及河川短小流急，使臺灣成為世界上雨水量豐沛但水資源缺乏的國家，因此河川基流量的評估變得十分重要。有鑑於此，本研究以乾濕季分明的臺灣南部作為研究區域，收集各流域主要水文測站資料，以基流分離、時間序列分析、基流歸因分析和小波分析探討基流量的特性，以及其與氣候特徵之間的關聯性。分析結果顯示，臺灣南部流域基流量呈現上升趨勢，降雨和蒸發散與基流量之間皆呈現顯著正相關，其中降雨的影響比蒸發散大。另外，敏感度分析顯示蒸發散和降雨的增加會導致基流的增加，這與降雨和蒸發散皆集中於濕季有關。基流歸因分析顯示，氣候變化對基流量增加的影響(75.0%)遠大於人為活動對基流量減少的影響(–2.9%)，表示氣候變化是影響臺灣南部流域基流量變化的主要因素。小波分析結果顯示，聖嬰-南方震盪(ENSO)和太平洋年代際震盪(PDO)與基流之間皆有負相關性，其中PDO的相關性大於ENSO，ENSO的時間尺度以4~8年為主，並且可能存在8年以上時間尺度；PDO的時間尺度以8年為主，並且在1年時間尺度上具有週期性的相關性變化。

Baseflow is among the most important components of streamflow. It is the main source of streamflow form groundwater systems in the dry season, and also plays an important role as a water resource in the ecological environment and for human activities. In recent years, because of climate change, the number of dry season days in Taiwan has increased, and the wet season has been delayed, resulting in fewer rainy days and increased precipitation intensity. In addition, the spatial distribution of rainfall is uneven, and rivers are short and fast-flowing, Taiwan has become a country with abundant rainfall but insufficient water resources; therefore, the assessment of baseflow is important. This study selected eight basins in Southern Taiwan with distinct wet and dry seasons as the research area. The baseflow characteristics and their relationships with climate features were assessed using baseflow separation, time series analysis, baseflow attribution analysis, and wavelet analysis. The results showed that baseflow has an increasing trend; both precipitation and evapotranspiration have a significant positive correlation with baseflow, and the impact of precipitation is greater than that of evapotranspiration. Sensitivity analysis showed that baseflow increases with increasing evapotranspiration and precipitation; this behavior is related to the concentration of precipitation and evapotranspiration in the wet season. Baseflow attribution analysis showed that the contribution of climate change to baseflow (75.0%) was larger than that of human activities (−2.9%), indicating that climate change was the main factor in the increase in baseflow. Wavelet analysis showed that both the El Niño−Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are negatively correlated with baseflow, where the PDO is more strongly correlated than the ENSO. The main time-scales of the ENSO and PDO are a 4−8-year band and an 8-year band, respectively. The ENSO may have a timescale above the 8-year band, and the PDO exhibits periodic correlation changes at a 1-year band.

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