Understanding long-term trends in hydroclimatic variables is important for future sustainable water resource management as it could show the possible regime shifts in hydrology. The main objective of this study was to analyze the homogeneity and trends of hydroclimatic data of Upper Awash Sab-Basin (UASB) in Oromia, Ethiopia, by employing homogeneity tests and Mann-Kendall and Sen’s slope tests. The data consist of 18 rainfall stations, 8 temperature stations, and 8 flow gauging stations across the UASB. Homogeneity and trends in streamflow, rainfall, and temperature variables were analyzed for the time period 1980 to 2017. In order to analyze homogeneity of hydroclimatic variables, we used four homogeneity tests (Pettitt’s test, Buishand’s test, standard normal homogeneity test, and von Neumann ratio test) at 5% significance level. Based on the outputs of four homogeneity tests, the results were classified into three categories, namely, “useful,” “doubtful,” and “suspect” to select the homogeneity stations. Mann-Kendall (Z) and Sen’s slope tests (Q) were applied for the selected homogeneous time series to detect the trend and magnitude of changes in hydroclimatic variables. The result showed that most of the stations in annual rainfall and streamflow data series were classified as useful. It is found that 58% of the rainfall stations were homogeneous. It is highlighted that 3 out of 8 discharge gauging stations have an inhomogeneity as they failed from one or a combination of the four tests. The MK revealed significant decreasing trends of annual rainfall in Addis Alem (Q = −19.81), Akaki (Q = −5.60), Hombole (Q = −9.49), and Ghinch (Q = −12.38) stations. The trend of annual temperature was a significant increasing trend in Addis Ababa Bole (Q = 0.05), Addis Ababa Tikur Ambessa (Q = 0.03), Tulu Bolo (Q = 0.07), and Addis Alem (Q = 0.06) stations. The results of discharge showed a significant increasing trend in Bega at Mojo (Q = 0.17) and Hombole (Q = 0.03) gauging stations. In general, the results obtained from discharge, rainfall, and temperature series indicated that most of the stations exhibited no trends in both annual and seasonal time series. It can be concluded that decreases in average annual rainfall totals and increases in mean annual temperature will probably drive sub-basin scale changes in discharge. We believe that the results obtained can fill information gaps on homogeneity and trends of hydroclimatic variables, which is very crucial for future water resource planning and management in the face of climate change.

中文翻译：

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埃塞俄比亚上阿瓦希河流域的长期均一性和水文气候变量趋势

了解水文气候变量的长期趋势对于未来的可持续水资源管理非常重要，因为它可能表明水文状况可能发生变化。这项研究的主要目的是通过使用均一性测试以及Mann-Kendall和Sen's斜度测试来分析埃塞俄比亚奥罗米亚上阿瓦什-萨宾-盆地（UASB）的水文气候数据的均一性和趋势。数据由UASB上的18个降雨站，8个温度站和8个流量测量站组成。分析了1980年至2017年期间的流量，降雨和温度变量的均一性和趋势。为了分析水文气候变量的均一性，我们使用了四个均一性检验（佩蒂特检验，比尚检验，标准正态均质检验和冯·诺伊曼比率测试）在5％的显着性水平。根据四个同质性测试的结果，将结果分为“有用”，“可疑”和“可疑”三类，以选择同质性测站。曼恩·肯德尔（将Z）和Sen的斜率测试（Q）用于选定的均质时间序列，以检测水文气候变量变化的趋势和幅度。结果表明，年降水量和流量数据系列中的大多数站都被归类为有用站。发现58％的降雨站是均匀的。需要强调的是，在8个排放测量站中，有3个存在不均匀性，因为它们在一项或多项测试中均失败了。MK揭示了亚的 斯亚丁（Q = −19.81），Akaki（Q  = −5.60），Hombole（Q  = −9.49）和Ghinch（Q = -12.38）个电台。亚的斯亚贝巴伯勒（Q  = 0.05），亚的斯亚贝巴Tikur Ambessa（Q  = 0.03），图卢博洛（Q  = 0.07）和亚的斯亚贝德（Q  = 0.06）站的年温度趋势呈显着上升趋势。放电结果显示，在Mojo（Q  = 0.17）和Hombole（Q = 0.03）计量站。通常，从流量，降雨和温度序列中获得的结果表明，大多数站点在年度和季节时间序列中都没有表现出趋势。可以得出的结论是，年平均降水总量的减少和年平均温度的增加可能会导致流域次流域规模的变化。我们认为，所获得的结果可以填补关于水文气候变量同质性和趋势的信息空白，这对于面对气候变化的未来水资源规划和管理至关重要。