Changes in ENSO Impacts on Ethiopia JJAS Precipitation in Recent Decades

Résumé fourni par la source

Ethiopia’s June-September (JJAS) rainfall is crucial for water resources, agriculture, and livelihoods, and exhibits pronounced interannual variability driven by extremely large-scale ocean-atmosphere interactions. The El Niño-Southern Oscillation (ENSO) has long been recognized as the primary source of this variability, exerting strong control on the strength and spatial distribution of Ethiopia’s summer rainfall. Using CHIRPS rainfall, ERA5 reanalysis fields, and ENSO and AMO climate indices, we employ correlation, regression, composite, and sliding-window analyses, complemented by moisture flux and circulation diagnostics. Results show a decline in the ENSO-JJAS rainfall correlation, weakening from r = −0.71 to r = −0.59, with strong relationships over central and northern Ethiopia becoming weak or statistically insignificant after 2001. AMO, on the other hand, has become more influential, with correlations increasing from r = 0.094 to r = 0.556. Atmospheric diagnostics indicate reduced ENSO-related circulation anomalies and moisture convergence over Ethiopia, alongside enhanced contributions to monsoon moisture transport from the Atlantic sector. These findings suggest a shift away from ENSO-dominated control toward a broader multi-basin influence, in which ENSO alone is no longer sufficient to explain JJAS rainfall variability. Therefore, seasonal forecasting systems for Ethiopia should incorporate Atlantic climate variability in addition to ENSO to improve predictive skill.

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