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Addis Ababa University (2019)

Spatio-temporal Analysis of Rainfall Trend in Upper Awash Basin

Regasa, Delesa

Titre : Spatio-temporal Analysis of Rainfall Trend in Upper Awash Basin

Auteur : Regasa, Delesa

Université de soutenance : Addis Ababa University

Grade : Master Science in Hydraulic Engineering 2019

This study examined spatio-temporal trend and variability of rainfall time series in the Upper Awash Basin. Rainfall records from twenty three stations for the period (1965-2016) of the major stations having longer observation period is used. The variability and trend significance (at α = 5% of two tailed) were studied at monthly, seasonal, and annual time scales. Data quality was checked by cumulative deviation and RAINBOW Software. Rainfall descriptive statistics is calculated by SPSS Software. Prewhitening has been applied to the Mann-Kendall test in the trend-detection of time series to eliminate the effect of serial correlation. Non-parametric Mann-Kendall test for trend significance analysis and Sen‘s slope estimator for trend magnitude in MAKESENS Excel template were used in determining the trend in rainfall. ArcGIS 10.2.2 is used to investigate the spatial interpolation. The coefficient of variation was used for rainfall variability analysis. As far as trend and variability analysis is concerned in space and time, the study area exhibited different trend and variability. Trend analysis with Mann-Kendall test show that, there is statistically significant increasing trend in annual total rainfall at Zequala station only where as statistically significant decreasing trend were found at Welenkomi, Addisalem, Bole, Akaki and Asgori stations. No significance trend was found for the remaining stations. For the trend magnitude with Sen‘s Slope Estimator, maximum rise in rainfall magnitude is 5.69mm/year while maximum decline is -5.1mm/year at Zequala and Welenkomi stations respectively. To observe spatial distribution of rainfall magnitude, trend and variability ; four interpolation methods (IDW, Kriging, Spline and Trend) have been used. Performance of each method is assessed by MAE, MSE, RMSE, MARE, MBE and MRE. Result obtained by IDW(less than 0.15 at all) gets minimum value and considered as high performance for this study. From the test statistics distribution map, western area show statistically significant decreasing whereas most parts of eastern shows statistically significance increasing trends. An even spatial distribution of trend is observed at central part of the study area. These findings provide valuable information on the distribution, variability and trend of rainfall necessary for the design of sustainable water resource management strategies and to reduce the impact of droughts and floods in the study area.


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