Rainfall variability and its teleconnection with atmospheric circulation anomalies over southern and southeastern region, Ethiopia

Factors related to rainfall variabilities in southern and southeastern Ethiopia have not yet been addressed. The extreme wet and dry events caused by atmospheric circulation patterns during the March-April-May periods were studied using 1991–2022 data from Climate Hazard Group InfraRed Precipitation with Stations (CHIRPS) and atmospheric circulation anomalies datasets. Empirical orthogonal function (EOF), precipitation concentration index (PCI), and coefficient of variation (CV) are used to determine the interannual variation. The study revealed that both PCI and CV exhibit rainfall variability with increasing magnitude from west to east of the region, while the first mode of EOF showed a dominantly uniform pattern and accounted for 48.8% of the observed variance. Eight extreme dry and four extreme wet years were also observed. Composite analyses suggested that the study area during wet years were characterized by convergence or divergence of velocity potential, and decrease or increase of vertical velocity at lower or upper troposphere which favorable conditions to vertical motion, while opposite phenomena observed during dry periods. Westerly winds from the southern Atlantic Ocean were associating with wet, while easterly winds from the Indian Ocean with dry. The study found a negative correlation between rainfall and Azores SLP, a positive correlation with Indian Ocean SST, and 62.5% of the driest periods coexisted with La Niña events. In summary, Indian Ocean SST, Nino Index 3.4, Azores SLP, South Atlantic 850-hPa westerly winds, and vertical velocity are predictive factors that should be considered in the rainfall forecasting process in the study area.