Comparative analysis of long-term precipitation trends and its implication in the Modjo catchment, central Ethiopia

Abstract

Understanding trends and variability of precipitation is essential to improve water resources utilization as well as agricultural activities. This study aims to investigate the spatiotemporal trends and variability of rainfall in the Modjo watershed, central Ethiopia. The Mann-Kendall trend (M–K) test, innovative trend analysis (ITA) and Sen’s slope estimator were used to determine temporal trends, while the inverse dis tance weighted interpolation technique was adopted to visualize the spatial trends in time series. The result showed that complex patterns of rainfall variability that range from 16 to 59%, 18 to 63%, and 50 to 90% for the annual, summer, and spring seasons, respectively was observed over the study watershed. The result also indicated that significant trend (p , 0.05) in annual rainfall was detected only in 28.6% and 42.9% of the stations under the M-K test and ITA method, respectively, which indicates relatively more significant trends are dis played by the ITA method than the M–K test. At the seasonal scale, positive trends have been more dominant in the summer season (Z . 0, SITA . 0), whereas negative trends (Z , 0, SITA , 0) were detected in the spring season. Comparatively, the ITA method is found to be robust and allows more detailed trend analysis results using graphical illustrations for extreme events. The study concludes that the increasing and decreasing trends in summer and spring rainfall patterns could have implications leading to an increase in extreme events and lower agri cultural productivity, respectively. The result suggests the need for planning effective adaptation strategies at the regional and local scales.