氣候變遷對半乾旱地區水文氣候與乾旱的影響：衣索匹亞比拉特流域的案例研究;Impact of Climate Change on Hydroclimate and Drought in Semiarid Regions: A case study in the Bilate Watershed, Ethiopia

NCUIR > College of Earth Sciences > Taiwan International Graduate Program for Earth System Science (NCU-Academia Sinica) > Electronic Thesis & Dissertation > Item 987654321/89585

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Title:	氣候變遷對半乾旱地區水文氣候與乾旱的影響：衣索匹亞比拉特流域的案例研究;Impact of Climate Change on Hydroclimate and Drought in Semiarid Regions: A case study in the Bilate Watershed, Ethiopia
Authors:	歐約瑟;Orke, Yoseph Arba
Contributors:	國際研究生博士學位學程
Keywords:	rainfall;temperature;streamflow;variability;changing points;Mann-Kendall test;hydrological impacts;RCPs;SWAT model
Date:	2022-07-13
Issue Date:	2022-10-04 11:46:51 (UTC+8)
Publisher:	國立中央大學
Abstract:	降雨在Bilate Wathershed (BW)扮演著重要角色，是該地區農業用水的主要來源，而農業在半乾旱地區受到氣候變遷的影響下將面臨許多挑戰，如農業減產、缺水和糧食安全。近年來，BW經歷更加頻繁且劇烈的水文氣候變化，因此探討水文與氣象因子的變化趨勢與程度，有助於為水資源管理和農業生產提供重要資訊。本研究首先使用變異係數 (coefficient of variation) 和標準化異常指數 (standardized anomaly index) 評估降雨、溫度和流量的變化，再利用變異點檢測方法、Mann-Kendell 檢測和 Sen 斜率計算，以量化其改變點和趨勢則。氣候變遷對BW的水文氣候影響，利用SWAT (Soil and Water Assessment Tool) 模型進行水文模擬，氣候推估資料來自CORDEX (Coordinated Regional Downscaling Experiment ) 資料庫，採用兩個代表性排放情境 (RCP4.5 和 RCP8.5)，評估 2021-2050 年和 2071-2100 年期間的氣候變化。對氣候變遷對乾旱的影響，則使用Standardized Precipitation Index (SPI)、Streamflow Drought Index (SDI) 和Reconnaissance Drought Index (RDI) 等三個乾旱指數來評估氣候變化對乾旱特徵的影響。分析結果主要發現，Bega (乾季) 和Belg (次要雨季) 的降雨量和逕流變化率高於Kiremt (主要雨季)，氣溫在 1990 年代初期為 0.91°C的上升趨勢，雨量在 1990年代後期有減少趨勢 (-11%)，流量則在 2000年代有減少趨勢 (-42%) 的減少趨勢，檢測到的變化點可能與ENSO事件有關。趨勢檢定顯示溫度有顯著的上升，最低溫 (0.06°C/年)的年均增幅比最高溫 (0.02°C/年) 顯著增加，年降雨量和流量呈現明顯下降趨勢，分別為8.32毫米/年和3.64毫米/年。隨著氣溫的大幅上升和降雨量的減少，流域的流量一直在減少，導致可用水量減少。前述變化趨勢對水資源管理和農業活動，應審慎考慮溫度升高與降雨量減少使可用水量更加不穩定，提早擬定調適措施。使用RCP8.5的氣變推估情境，氣溫將大幅上升，到21世紀蒸發量將增加16.8%，預計年平均降雨量將減少38.3%，導致流量減少高達37.5%，日夜溫差變小可能有利於作物生長，但同時也會因高溫產生不利影響。氣候變遷下，三種不同乾旱指數的強度皆增加，顯示未來乾旱的發生機率在遠期將更高，這些預期影響將加劇水資源短缺並對糧食安全產生衝擊，本研究結果包含過去氣候水文變化趨勢及未來氣變衝擊影響之水文氣候與乾旱，可以提供水資源管理當局和決策者提供可信賴的量化資訊，以盡早擬訂因應未來氣候變遷的有效調適措施。 ;The livelihood of communities in the Bilate Watershed (BW) depends mainly on rain-fed agriculture. The effects of the erratic nature of hydroclimatic variables, such as reduction of agricultural production, scarcity of water, and food insecurity, are widespread in the semi-arid regions. The Bilate Watershed has experienced more frequent and intense spatiotemporal hydroclimatic variability in recent years. Therefore, it is essential to understand variations in hydrometeorological variables to provide crucial information for water management and agriculture. The coefficient of variation (CV) and the standardized anomaly index (SAI) were used to assess the variability of rainfall, temperature, and streamflow. Changing point detection methods, the Mann–Kendell test, and Sen’s slope estimator were employed to detect shifting points and trends of the variables in the watershed. The impact of climate change on hydrometeorology of the Bilate Watershed was assessed by the Soil and Water Assessment Tool (SWAT) model using climate projections under two Representative Concentration Pathways (RCP4.5 and RCP8.5) obtained from the Coordinated Regional Downscaling Experiment (CORDEX) Africa during 2021-2050 and 2071-2100. Moreover, the impact of climate change on droughts characteristics was also assessed by applying three drought indices such as the standardized precipitation index (SPI), streamflow drought index (SDI), and reconnaissance drought index (RDI). Rainfall and streamflow showed higher variability in the Bega (dry season) and Belg (minor rainy season) than in the Kiremt (main rainy season). Temperature exhibited an upward shift of 0.91 °C in the early 1990s. A decline in rainfall (-11%) and streamflow (-42%) were found after changing points around the late 1990s and 2000s. The changing points detected were likely related to the ENSO events. The trend test identified a significant increase in temperature with a faster increase in minimum temperature (0.06 °C/year) than maximum temperature (0.02 °C/year). Average annual rainfall and streamflow showed significant declining trends of 8.32 mm/year and 3.64 mm/year. With this substantial increase in temperature and decline in rainfall, the watershed has been experiencing a reduction in streamflow and exacerbating the lack of available water. Adaptation measures should be developed by considering the increasing temperature and rainfall′s declining and erratic nature for water management and agricultural activities. Due to the profound rise in temperature under the RCP8.5 scenario, evapotranspiration will increase by 16.8% by the end of the 21st century. Average annual rainfall is projected to decrease by 38.3%, leading to a decrease in streamflow up to 37.5%. Projections in reduced diurnal temperatures may benefit crop growth but intensify heat stress. The probability of drought is expected to double in the far period with increased intensity for all three drought types. These expected impacts will exacerbate water scarcity and threaten food security in the study area. The study results provide promising quantitative information to water management authorities and decision-makers to develop adaptive measures to cope with the changing climate.
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