| 摘要: | 阿瓦什河流域（ARB）的農業生產主要依賴天然降水。降雨異常的影響將使農業生產力下降與缺水，甚至造成糧食危機，這些都越來越嚴峻。近年來，ARB的降雨在空間和時間上都出現更加頻繁與強烈的異常。分析降雨變化和趨勢，將有助於提高農業生產管理效率。在ARB中進行了1986-2016年期間29個氣象站的溫度和降雨變化點檢測分析，包含馮·諾伊曼比率，佩蒂特氏，比尚範圍（BR）和標準正態均勻性（SNH）以及曼恩·肯德爾趨勢測試（MK),。並使用五個乾旱指數來探討2002-2017年期間頻繁的乾旱現象，這五個乾旱指數分別是儲水赤字指數（WSDI），蒸發應力指數（ESI）,標準降水蒸散指數（SPEI）, 標準降水指數（SPI）和蒸發需求乾旱指數（EDDI）。此外，也使用HydrologiskaByr?nsVattenbalans-avdelning（HBV）模式搭配六種氣候情景（ECHAM-A2，IPSL-A2，IPSL-RCP4.5，MPI-RCP4.5，MPI- RCP8.5，IPSL-RCP8.5）評估2021-2050年及2071-2100年之水文循環變化。
在整個ARB的MK趨勢測試顯示，溫度的年和季節尺度是顯著增加。在2001/02年和1997/98年分別檢測到主要雨季（MRS）（6月至9月）和次要雨季（mRS）（2月至5月）的溫度變化點。對於降雨，ARB的下游部分變化很大，並且趨勢和均值變化明顯減少。BR和SNH的測試結果顯示，mRS降雨變化點在1997/98年，隨後每年減少52.5 mm。每年和MRS期間降雨的增加（或減少）與聖嬰（ElNi?o）事件有高度關聯。mRS中降雨的顯著下降趨勢和變化點與印度洋和大西洋的持續變暖，局部變暖以及反聖嬰事件有關， ARB的降雨異常對該地區的農業構成了嚴峻挑戰。因此，至關重要的是，在ARB，特別是在下游地區，建立適當的綜合水管理和儲水技術。
從2002年至2017年的MK檢驗發現，年度和季節性陸地儲水量指數（TWS）顯著增加，這有利於流域的灌溉和其他經濟活動。根據儲水不足指數（WSD），在2005 / 01-2006 / 03中發現了持續15個月的最嚴重乾旱，總WSD為-411.8 mm，2005/03年的峰值不足指數為-46.24 mm，表明流域總TWS極度短缺。使用SPI，ESI，SPEI和EDDI，可檢測在2002、2008-2009年、2012-2013年和2015年的持續乾旱，而乾旱的嚴重性（強度）在2009之後比以前降低。除了一般的乾旱外，還使用ESI和EDDI指數在ARB中檢查了爆發式乾旱。因此，ARB的農業用地，草地，植被覆蓋的地區和沿河的灌溉耕地容易出現乾旱。與ESI相比，使用EDDI檢測到的爆發式乾旱程度更大，因為ESI依賴於土壤水分和植被覆蓋度。發現下游流域特別是在MRS和mRS的最後兩個月中，極易遭受此類型乾旱。EDDI可以及早發現爆發式乾旱的開始，可以將其用作預警，以最大程度地減少流域內農業作物的損失和與乾旱有關的風險。總體而言，3個月和6個月的乾旱指數可以最好地預測ARB的氣象和農業乾旱狀況。
高人口密度，多樣化的生態以及上游ARB（MK子盆地）以天然降水為主的農業，氣候影響分析對該地區至關重要。所有GCM下溫度的升高會增加蒸發散量，造成MK盆地的水分流失。然而，最低溫度的升高可以減少作物的冷害。所有GCM（不包括ECHAM-A2）下的年降雨量和MRS降雨量和流量都會增加。使用RCP8.5，在近期（2021-2050）和遠期（2071-2100）期間的年降雨量分別增加38％和57％；在近期（2021-2050）和遠期（2071-2100）期間，流量預計分別增長23％和49％。大多數GCM的推估流量增加將提高8月的洪災風險，而ECHAM-A2的流量減少將加劇現有的水資源短缺，特別是在mRS中。總體而言，MRS期間的儲水規劃對減少乾季缺水的影響至關重要。這些發現將有助於該盆地的社區和水資源管理者建立適當的調適措施，以進行有效的水資源管理。
;The community′s livelihood in the Awash River basin (ARB) is mainly reliant on rainfall-dependent agriculture. Effects of rainfall anomalies such as reduction of agricultural productivity, water scarcity, and food insecurity are becoming more prevalent in this area. In recent years, the ARB experienced more frequent and intense spatio-temporal rainfall anomalies, which make the shift and trend analyses of rainfall associated with sea surface temperature crucial for providing guidance to improve food security. Change-point detection tests (e.g., the von Neumann ratio, Pettit′s, the Buishand′s Range (BR), and the Standard Normal Homogeneity (SNH)), and the Mann-Kendall trend-test analysis (M-K) of temperature and rainfall were carried out for the ARB from 29 meteorological stations during the period 1986-2016. The frequent drought reoccurrences were also characterized using five drought indices, including the Water Storage Deficit Index (WSDI), the Evaporative Stress Index (ESI), the Standardized Precipitation Evapotranspiration Index (SPEI), the Standardized Precipitation Index (SPI), and the Evaporative Demand Drought Index (EDDI) during the period 2002-2017. Moreover, the impact of climate change on the hydrology of upstream ARB was assessed by Hydrologiska Byr?ns Vattenbalans-avdelning (HBV) model using six scenarios during 2021-2050 and 2071-2100.
The M-K trend test over the entire ARB showed a significant increasing trend in annual and seasonal temperature. Temperature change-points for the major rainy season (MRS) (June-September) and the minor rainy season (mRS) (February-May) were detected in 2001/02 and 1997/98, respectively. For rainfall, the downstream part of the ARB experienced high variability, significant decreasing trend, and shift in mean values. The BR and SNH test results showed that the mRS rainfall change-point was around 1997/98, with a subsequent annual decrease of 52.5 mm/yr. The increase (decrease) of rainfall in the annual and MRS periods is attributed to effects of the La Ni?a (El Ni?o) events. The significant decreasing trend and change-point of rainfall in the mRS is associated to the steady warming of the Indian and Atlantic Oceans, local warming, and the La Ni?a events, which explained that rainfall anomalies in the ARB are posing a serious challenge to agriculture productions in the area. It is therefore essential that appropriate integrated water management and water-harvesting technologies should be established in the ARB, especially in the downstream areas.
The M-K test from 2002 to 2017 detected a significant increase in annual and seasonal terrestrial water storage (TWS), which is advantageous to irrigation management and other increasing economic activities in the basin. Based on water storage deficit (WSD), the most severe drought that lasted for 15 months was detected around 2005/01-2006/03 with a total WSD of -411.8 mm with a peak deficit of -46.24 mm in 2005/03, indicating an extreme shortage of TWS in the basin. Persistent droughts were identified in 2002, 2008-2009, 2012-2013, and 2015 by SPI, ESI, SPEI, and EDDI, showing less intensified drought after 2009. In addition to the conventional drought, flash drought was also examined in ARB using ESI and EDDI indices. Results showed agricultural/grass-lands, vegetation, and irrigational cropland areas were prone to flash drought in ARB. The extent of flash drought detected by the EDDI was more extensive as compared to those by the ESI due to soil moisture and vegetation coverages were considered in the ESI. The downstream part was found to be highly susceptible to flash drought, especially in the MRS and the last two months of mRS. The EDDI can early detect the start of the flash drought, which can be used as an early warning precursor to support the planning of adaption measures to reduce agricultural crop losses and drought-related risks in the basin. Overall, the 3- and 6-monthly drought indices can best predict the onset and severity of meteorological and agricultural droughts in ARB.
Considering impacts of climate change, the upstream ARB (MK subbasin) is highly vulnerable due to high population density, diverse ecology, and mainly rainfed agriculture. The projected increase in temperature under all GCMs considered in this study will increase the evapotranspiration that induces more water loss in MK subbasin. Nevertheless, the risk of crop chilling damage will be reduced as the projected increase in minimum temperature. The annual and MRS rainfall and streamflow are projected to increase by all GCMs, excluding ECHAM-A2. Under RCP8.5 scenarios, annual rainfall (streamflow) is expected to increase by 38% (23%) and 57% (49%) during 2021-2050 and 2071-2100, respectively. The projected streamflow increase by most of the GCMs may increase flood risk mainly in August, while the streamflow decrease by ECHAM-A2 will exacerbate the existing water shortage, especially in the mRS. Overall, water harvesting during the MRS would be vital to minimizing the adverse effects. These findings will help the community and water managers of the subbasin to establish suitable adaptation measures for viable water resources management |
