Abstract
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.
Highlights
Climate change impacts will felt through altering patterns of agricultural production and water availability, with an increase in temperature and changing the rainfall patterns. e climate of the Earth has been changing through time [1].According to Intergovernmental Panel on Climate Change (IPCC) assessment reports (2014), for instance, compared to any preceding decade since 1850, Earth’s surface temperature has been reported to be successively warmer for the last three decades [2]
And annual data from each rainfall and streamflow station are tested by the four homogeneity tests (Pettitt’s, standard normal homogeneity test (SNHT), Buishand range test (BRT), and von Neumann ratio (VNR)). e annual and seasonal temporal trend analysis of rainfall, temperature, and streamflow time series were performed using Mann-Kendall methods at a 5% level of significance at each station. e monthly and annual homogeneity tests analyses were followed by spatial-temporal trend analyses of selected seasonal and annual hydroclimatic time series
We presented the application of different statistical tests to analyse homogeneity and trends in rainfall, temperature, and discharge in the Upper Awash sub-basin (UASB) in Ethiopia for a period of nearly four decades, 1980 through 2017. e homogeneity of the annual and monthly rainfall and discharge data series of Upper Awash Sab-Basin (UASB) was studied using four statistical tests; Pettitt’s test [34], SNHT [52], BRT [32], and VNR [35]. e rainfall and discharge data series were analyzed at a 0.05 significance level for each homogeneity test separately
Summary
Climate change impacts will felt through altering patterns of agricultural production and water availability, with an increase in temperature and changing the rainfall patterns. e climate of the Earth has been changing through time [1].According to Intergovernmental Panel on Climate Change (IPCC) assessment reports (2014), for instance, compared to any preceding decade since 1850, Earth’s surface temperature has been reported to be successively warmer for the last three decades [2]. Climate change impacts will felt through altering patterns of agricultural production and water availability, with an increase in temperature and changing the rainfall patterns. Is indicates that it is in recent years that the effect of climate change has been felt through abrupt changes in hydroclimatic system at various spatial scales, agricultural production, and water availability [3, 4]. E change in both local and global climate, magnitude, and pattern of temperature and rainfall affect the rate and occurrence of hydrologic phenomena such as drought and flood. In response to change in climate, there is a marked tendency towards a decrease in the water resources and with a consistent increase in drought severity and duration [21]. Characterizing precipitation and flow trends is crucial for any design of sustainable water management strategies and to reduce the impact of droughts and floods [18, 22, 23]
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