Indian Ocean Dipole Impacts on Eastern African Short Rains Across Observations, Historical Simulations and Future Projections

Eastern African “short rains” (October–December) are significantly influenced by the Indian Ocean Dipole (IOD), with increased rainfall during positive IOD events and dryness during negative IOD events. Most Coupled Model Intercomparison Project Phase 6 models overestimate the short-rain response to IOD events in Eastern Africa, especially during negative events. This is due to enhanced zonal moisture transport anomalies, mainly related to amplified IOD intensity and the westward extension of the IOD eastern core. Mean-state precipitation biases further contribute to overestimated short rains, traced back to the mean-state positive IOD-like biases. Under global warming, the contrasting short-rain responses to IOD in the Horn of Africa and Southeastern Africa are primarily driven by the westward-shifting IOD circulation. Enhanced impacts in the Horn of Africa are driven by stronger IOD-related zonal winds and the more humid mean-state atmosphere which is attributed to the IOD-like warming pattern. In contrast, weakened impacts in Southeastern Africa are associated with anomalous meridional wind changes. Additionally, due to more extreme negative IOD events, the frequency as well as severity of droughts in the Horn of Africa are projected to increase. These findings provide valuable insights into Eastern Africa's climate dynamics and inform climate adaptation strategies.