Trends and variability in annual and seasonal rainfall amount and timing in Wereilu district, Northeastern Highlands of Ethiopia

Abstract

• Moderate to high temporal variability was observed across the different seasons. • Significant but contrasting trends were observed for both the main and short rainy seasons. • Both monotonic and non-monotonic trends were detected in annual and seasonal rainfall patterns. • The mean rainfall amount and its timing has changed over time. • The observed change in rainfall highlight the need for adaptive strategies at the local level. • Rainfall variability is more pronounced during the short rainy season compared to the main rainy season. Studying climate change can significantly benefit agricultural practices in a country where many people rely heavily on subsistence farming. To this end, this study aimed to examine trends and variability in rainfall amounts and timing in the climate-vulnerable Wereilu district, northeastern highlands of Ethiopia. The coefficient of variation and standardized rainfall anomaly were employed to analyse rainfall variability, while the Innovative Trend Analysis (ITA) was applied to examine rainfall trends. The findings revealed that Kiremt (main rainy season) exhibited moderate variability, whereas Belg (small rainy season) exhibited high variability. The trend analysis showed significant changes in both seasonal and annual rainfall amounts and their timing. Annual and Kiremt rainfall significantly increased at Wereilu by 55.5 mm and 88.7 mm per decade, respectively, and at Kabie by 16.6 mm and 48.4 mm per decade ( p < 0.01). In contrast, Belg rainfall revealed a significant declining trend at both sites. The graphical trend analysis revealed a positive trend for all clusters during Kiremt. In contrast, Belg showed a declining trend across all clusters, with a more pronounced decline in higher values at both sites. Rainfall onset dates significantly shifted towards earlier onset, while rainfall cessation dates showed insignificant late cessation. The length of the rainy season exhibited a positive trend ( p < 0.01) at Wereilu and ( p < 0.05) at Kabie. Overall, the observed substantial changes in rainfall amounts and timing imply the need for relevant adaptation measures, particularly in the farming system and water sector.