近年氣候異常導致乾旱事件增加，臺灣經常面臨水資源短缺問題，對社會經濟和生態系統造成嚴重影響，因此瞭解乾旱是非常重要的。本研究採用2013年至2022年的Landsat 8衛星影像、降雨以及溫度資料，計算溫度植生乾燥指數 (Temperature Vegetation Dryness Index, TVDI)、改進型溫度植生乾燥指數 (improved Temperature Vegetation Dryness Index, iTVDI)、常態化差異乾旱指數(Normalized Difference Drought Index, NDDI)以及標準化降水指數(Standardized Precipitation Index, SPI)等四種乾旱指數，探討近十年濁水溪沖積扇的乾旱時空變化。為檢驗上述乾旱指數的合理性，本研究將乾旱指數與土壤含水量和土地利用/土地覆蓋比較分析。研究結果顯示，TVDI和iTVDI在平原區呈現相似的變化，但在山區的差異較大，以土壤含水量數據作為依據，iTVDI的準確性優於TVDI。時間上，iTVDI在乾季(11月至隔年4月)為0.62 ± 0.03，屬於乾旱範圍；濕季(5月至10月)為0.54 ± 0.06，屬於正常範圍。此外，在2015、2018和2021年均出現乾旱事件。空間上，濁水溪沖積扇沿海和山區iTVDI值比扇央區域低，顯示扇央區域較容易發生乾旱，且濕潤和乾燥區域的空間位置不會隨時間改變。另外，土地利用/土地覆蓋分析結果與iTVDI比較，顯示濕潤區域主要位於研究區域東部林地區域與西部水體區域，作物和建地為主的草地和裸地較乾燥。最後，TVDI、iTVDI、SPI和NDDI相關性分析結果顯示，顯示乾旱程度隨著降雨減少或植被減少而增加。本研究透過衛星影像資料分析乾旱的時空變化，可為乾旱監測和水資源管理提供參考，減輕乾旱對社會、經濟和環境的影響。

In recent years, the increase in drought events due to abnormal climate change has caused Taiwan to frequently face water scarcity problems, which have had severe impacts on the social economy and ecological systems. Therefore, understanding drought is very importance. This study utilized Landsat 8 satellite imagery, rainfall, and temperature data from 2013 to 2022 to calculate four drought indices, including the Temperature Vegetation Dryness Index (TVDI), improved Temperature Vegetation Dryness Index (iTVDI), Normalized Difference Drought Index (NDDI), and Standardized Precipitation Index (SPI), to investigate the spatiotemporal variations of drought in the Choushui River Alluvial Fan over the past decade. To verify the rational of the drought indices that mention above, this study compared the drought indices with soil moisture and land use/land cover data. The results show that TVDI and iTVDI exhibited similar variations in the plain areas, but had greater differences in the mountainous areas. Based on the soil moisture data, the accuracy of iTVDI was superior to that of TVDI. In terms of time, the iTVDI value was 0.62 ± 0.03 during the dry season (November to April of the following year), which falls within the dry range, and 0.54 ± 0.06 during the wet season (May to October), which falls within the normal range. Additionally, drought events occurred in 2015, 2018, and 2021. In terms of region, the iTVDI values in the coastal and mountainous areas were lower than in the central fan area, indicating that the central fan area has a higher possibility for drought occurrence, and the regional positions of the wet and dry areas do not change over time. Furthermore, the comparison of the land use/land cover analysis results with the iTVDI showed that the wet areas were mainly located in the eastern forested regions and western water body areas of the study region, while the grasslands and bare lands dominated by crops and building areas were more dry. Finally, the correlation analysis results among TVDI, iTVDI, SPI, and NDDI showed that the drought severity increased as rainfall decreased or vegetation decreased. This study’s analysis of the spatiotemporal variations of drought using satellite imagery data can provide a reference for drought monitoring and water resource management, aiming to lessen the impacts of drought on society, the economy, and the environment.

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