Annual and seasonal rainfall trend analysis using gridded dataset in the Wabe Shebele River Basin, Ethiopia

Long-term rainfall trends analysis under climate change, particularly in developing countries where rainfed agriculture is substantial, is vigorous to evaluate rainfall variability brought changes and propose possible adaptation measures. Hence, the study was designed to evaluate annual and seasonal long-term trends in rainfall in Wabe Shebele River Basin in Ethiopia using gridded monthly precipitation data derived from Climate Research Unit (CRU TS 4.1) with 0.5 degrees x 0.5 degrees resolution from 1920 to 2019 years. The time series trend of annual and seasonal rainfall was detected by employing innovative trend analysis (ITA). The results were compared with the most widely used Mann-Kendall (MK) test and Sen's slope estimator method. The basin was sub-divided into ten sub-basins for easy analysis. The MK test result revealed a non-significant decrease in annual and seasonal rainfall trends that occurred in most sub-basins and the entire basin. The results of the ITA method showed that the scattered plot was accumulated on the 1:1 (45 degrees) straight line, indicating no trend for most of the sub-basins. The trends vary within sub-basins and rainfall magnitude while the decreasing and increasing trends were within +/- 10%. The finding indicates that statistics for phi are non-uniform spatial and temporal and show no significant trends at a 5% significant level in the most sub-basins. The comparison of the three selected methods indicates that ITA performs better in trend investigation. Hence, the ITA method provides results in graphical form, which makes a straightforward interpretation of trends based on rainfall intensity. Rainfall trends investigation is vital for agricultural development where combining the possible adaptation measures to climate change is vigorous during water resources planning and development for agriculture. Accordingly, the strategic plan is recommended for the practical activity of agriculture by considering the decline and variability of rainfall patterns in the sub-basins particularly and in the basin generally.