Flow Indices Variability in Humid Subtropical of Upper Awash River Basin, Ethiopia

Abstract

Investigating the hydrological extremes indices at high resolutions describing the whole stream spectrum is essential for the comprehensive assessment of watershed hydrology. The study focuses on a wide-ranging assessment of river discharge in annual mean, peak, and high and low percentiles flow at the Upper Awash River basin, Ethiopia. Statistical tests such as coefficient of variation, flood variability to characterize the flow regime and Tukey’s test to detect decadal variability. Modified Mann-Kendall test, Sen’s slope estimator, innovative trend analysis and Pettitt’s test were applied to see trends, and change points in time series, respectively. Results showed that the basin was characterized by moderate to high variability. Spatially, main tributaries showed a higher variability, almost in all-time step and characterized by higher flood variability. The large discharge receiving rivers resulted in a moderate to high and lower discharge variability. Test statistics resulted in a positive increasing trend dominating most time scales at a 5% significant level and higher magnitude of slope trend in peak flow. A negative trends were also exhibited. Hombole main outlet site experienced decreasing trend in high percentile flow. In comparison, complete trend direction agreements were observed (except in few series). Flow indices showed an upward shift and downward shift mainly in the year 2000s and the significant decadal variation resulted in comparable with change points. The study provides an understanding of water resources variability, which will be necessary to apply operational water resources strategies and management to restrain the potential impacts of variability nature of the streamflow.