Long-Term Rainfall Dynamics and Trend Assessment Using Observed and Gridded Satellite Precipitation Products and Implications for Climate Change Adaptation over Modjo Catchment, Ethiopia

The evaluation of long-term rainfall variability and trends in the context of a changing global climate is essential for developing effective adaptation strategies. It is also important to analyze trends using global precipitation products. The objective of the present study was to assess the long-term trends in annual and seasonal rainfall over the Modjo catchment in central Ethiopia by utilizing both observed and satellite precipitation products, CHIRPS and PERSIANN-CDR. The study employed CV and PCI to evaluate the variability and monthly rainfall concentration within the catchment. The Sen Slope Estimator, Mann-Kendall test, and Innovative Trend Analysis were used to assess the trends within the data series. The results indicate that annual and Kiremt rainfall showed low to moderate variability at all stations, whereas the Meher, Bega, and Belg seasons exhibited high variability, with CV values exceeding 30%. The PCI values indicated that the annual rainfall data series exhibited a moderate and irregular distribution, while the seasonal rainfall distribution displayed a highly irregular pattern, with all values exceeding 20. The MK and SSE trend analysis revealed no significant trends (at α = 0.05) in the annual rainfall across all stations; however, significant trend changes were observed in the seasonal rainfall datasets. Additionally, Trend analysis revealed a significant decrease in most Bega season trends (at α = 0.05, α = 0.01), whereas Kiremt and annual seasons showed similar patterns. Conversely, the Meher season showed an increasing trend with no significance at α = 0.05. The ITA shows trends similar to MK and SSE, but with different significance levels. In the analysis, 22% of the data was insignificant, while the rest was significant at a 95% confidence level. The study reveals temporal dynamics in rainfall trends, underscores important implications for climate change adaptation, and offers valuable insights for planning effective adaptation measures.