Analysis of trends and variability of hydroclimate variables in the Didessa Sub-basin: Implications for the Upper Blue Nile (Abbay) Basin, Ethiopia.

Long-term trends and variability of hydroclimate variables significantly impact water resources. This study aims to investigate trends and variability of hydroclimate variables in the Didessa sub-basin. Modified Mann-Kendall and Sen's slope estimators were used to analyze the trends. At the same time, variability was assessed using the standardized anomaly index (SAI), precipitation concentration index (PCI), and coefficient of variation (CV). The seasonal and annual rainfall trend analysis results showed an increasing tendency, except for the winter. The PCI and SAI results for most of the stations in the sub-basin exhibit moderate rainfall concentration. The sub-basin mean temperature showed a significant upward trend, with annual average rates of +0.02 °C. Analysis of streamflow at Arjo and Bunobedele stations showed a significant upward trend of 0.5 m/s/yr and 0.015 m/s/yr, respectively, in the spring season. Mixed trends were observed at upstream stations; Big Anger exhibits a downward trend with a declining rate of 3.04 m/s/yr, while Little Anger displays a rising trend with an increasing rate of 0.25 m/s/yr. Flow data at upstream and downstream gauged stations positively correlated with mean rainfall. The findings of this study have significant implications for water resource management and climate change mitigation by giving insight to policymakers and water resource managers in developing adaptation strategies for changing hydroclimate conditions to ensure sustainable water utilization globally.