Hydrological Trend Variability And Time Series Modeling Of Weyib Catc

The main goal of this study is to assess trend, spatio- temporal variability of rainfall and runoff,rnand time series modeling of major tributaries of Weyib River catchment, which is located inrnGenale Dawa basin between 6022’ to 7006’N and 39037’ to 41015’E. Stream flow records fromrnsix flow-gauging stations in four major river catchment of the weyib between (1981- 2008) andrnsix precipitation stations all over the weyib catchment between (1984-2014) were studied atrnmonthly, seasonal, and annual scales. In the study, the data were firstly subjected to qualityrnchecks through the cumulative deviations test and the standard normal homogeneity test. Torndetect correlation Lag-1 autocorrelation coefficient was used. ArcGIS 10 environment is used torninvestigate the spatial variability. The Coefficient of Variation (CV) was used for variabilityrnanalysis. Mann-Kendall trend analysis and Sen’s slope estimator in MAKESENSE version 1.0rnExcel template are used in determining the changes in the rainfall and runoff. ARIMA model inrnMinitab 17 Statistical software was used for time series modeling. By using statistical measurern(R2, AIC and BIC) it was determined that, ARIMA time series model is better appropriate tornstream flow forecasting. The interesting observation is that all sub catchment of the Weyibrncatchment for both rainfall and runoff exhibit different behavior as far as trend and variabilityrnanalysis is concerned. Trend analyses with Mann-Kendall test show that, there is increase inrnsignificant trend in annual mean runoff at Togona and Tebel station while the other four stationsrn(Shaya, Agarfa, Alemkerem and Denbel) shows no significant trend. From precipitation stations,rnonly Ginir station shows significant increasing trend in annual basis. The direction of rainfall andrnrunoff trend was, in general, upward and statistically significant (upward) trends (95% to 99.9%)rnsignificant levels were observed. Global climate change influence on the changes in rainfall andrnrunoff characteristics was not conclusive. The key conclusion is that, the results of this study arernexpected to assist water resources managers and policy makers in making better planningrndecisions in the Weyib River catchment.rnKeywords: Weyib River catchment ; Minitab 17 ;Trend analysis ;Precipitation ; Mann-KendallrnTest ; Sen’s Slope Estimator; probability distribution

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