The possible linkage of ENSO and IOD to JJAS rainfall variability over Ethiopia

Abstract Rainfall variability in Ethiopia is strongly influenced by large-scale sea surface temperature (SST) anomalies, notably the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). This study examines June–September (JJAS) rainfall from 1991 to 2020 using multiple datasets and statistical methods, including t-tests, empirical orthogonal functions (EOF), composite analysis, correlation, and linear regression. The first EOF captures 64.4% of total rainfall variance and shows contrasting variability between northwest and southeast regions, effectively representing interannual JJAS rainfall patterns. Circulation analyses reveal that above-average rainfall is associated with lower pressure systems, enhanced convection, anomalous convergent flows, and positive water flux anomalies, while below-average rainfall corresponds to opposite conditions. ENSO shows a significant correlation with JJAS rainfall (r = − 0.66), while IOD exhibits a weaker but regionally relevant influence (r = 0.2), particularly in eastern Ethiopia. Warm SST anomalies in the central equatorial Pacific (El Niño) induce high pressure, positive outgoing long wave radiation, and subsidence over Ethiopia, reducing rainfall, whereas La Niña conditions enhance rainfall. IOD phases modulate low-level convergence and divergence patterns, further influencing regional precipitation. These results highlight the complex interplay between ENSO, IOD, and tropical circulation in shaping Ethiopia’s main rainy season, providing critical insights for planning, mitigation, and climate adaptation strategies.