Evaluation of rainfall patterns and spatiotemporal variability: the case of Gurage Zone, Ethiopia

This study presents the first comprehensive assessment of rainfall trends and variability in Ethiopia's Gurage Zone, employing Sen's slope estimator, the Mann–Kendall (MK) test, and innovative trend analysis (ITA), complemented by the coefficient of variation (CV) and standard anomaly index (SAI) metrics. The results revealed high rainfall variability (CV = 18.14–158.8%), particularly in the summer (Kiremt) and spring (Tsedey) seasons within highland agroclimatic regions. Seasonal distribution showed maximum rainfall in the summer (1,045.18 mm) and minimum in the winter (43.29–102.25 mm). Spatially, the northwestern areas received higher rainfall than the eastern parts. The trend analysis indicated a significant decreasing trend in the winter, with Buie (Z = −2.93) and Koshe (Z = −2.94) showing the strongest declines. Additionally, Butajira and Ejersalele stations exhibited significant monthly trends at the 10% level, with January showing the most pronounced decline. Overall, the findings highlight substantial rainfall variability and declining trends, offering critical, novel insights for climate research, policy formulation, and strategic water resource management in an area previously unexamined.