Detecting Hydrological Variability in Precipitation Extremes: Application of Reanalysis Climate Product in Data-Scarce Wabi Shebele Basin of Ethiopia

Abstract

Understanding climate data is essential for water resource management, flood risk assessment, agricultural planning, ecological modeling, and climate change adaptation. This study investigated the trends and variability of precipitation extremes to explore statistically significant trends in extreme hydrological conditions over the last 35 years in the Wabi Shebele basin of Ethiopia. Two reanalysis climate products: Enhancing National Climate Services (ENACTS) and Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) were evaluated against ground observations using cumulative distribution function and statistical measures. The result shows that the CHIRPS data set performed well and captured the precipitation extremes measured by rain gauges. The Mann–Kendall trend test analysis conducted using three extreme precipitation indices: annual maximum precipitation (AMP) (i.e., annual highest 1-day precipitation amount), R10 (i.e., the yearly count of days when precipitation ≥10 mm), and R95P (i.e., 95% percentile precipitation events). The result indicates an increasing tendency over the western–eastern highland and southern part of the basin; In contrast, it indicates decreasing trends over the middle of the study area. Quantile perturbation analysis using R95P reveals high oscillations at 5-year intervals within a confidence interval (CI), particularly at the basin’s western–eastern highlands and southern lowlands. Since the 2000s, a periodicity analysis of maximum yearly precipitation using the autocorrelation function has revealed cycles at 2-year to 5-year intervals over the western–eastern highlands of the basin.