Twenty‐First Century Projections and Trends of <scp>JJAS</scp> Rainfall Over the Greater Horn of Africa Under <scp>CMIP6</scp> Shared Socioeconomic Pathways Scenarios

ABSTRACT Understanding future changes in seasonal rainfall over the Greater Horn of Africa (GHA) is critical, given the region's heavy reliance on June–September (JJAS) precipitation for agriculture, water resources and livelihoods. This study examines projected changes in June–September (JJAS) rainfall over the GHA using Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations under three Shared Socioeconomic Pathways (SSP126, SSP245 and SSP585). Projections are derived from CMIP and ScenarioMIP experiments using six top‐performing models (CESM2, CESM2‐WACCM, EC‐Earth3, GFDL‐ESM4, HadGEM3‐GC31‐MM and MPI‐ESM1‐2‐HR), selected based on their skill in reproducing historical JJAS rainfall. Changes are assessed for the near‐term (2021–2040), mid‐term (2041–2060) and long‐term (2081–2100) relative to the 1995–2014 baseline. The analysis focuses on key JJAS rainfall‐dependent regions, including the Ethiopian Highlands and western GHA sub‐regions and examines both trend behaviour and spatial patterns of projected precipitation change. Results indicate a general tendency toward increased JJAS rainfall across parts of the GHA under the high‐emission SSP585 scenario, with half of the models and the multimodel ensemble (MME) showing significant wetting, although projections exhibit pronounced spatial heterogeneity and inter‐model variability. In contrast, SSP126 and SSP245 exhibit weak and spatially inconsistent trends, with no uniform regional signal in the MME. Regions that climatologically receive little JJAS rainfall are projected to experience a change in rainfall of up to ~40% across all future periods, although the direction and magnitude of these changes vary among models and emission scenarios. Regional discrepancies among models remain substantial, especially over the Ethiopian Highlands and Sudan region, reflecting the complex influence of large‐scale circulation dynamics, regional climate drivers and topographic effects. Projected rainfall changes are dynamically consistent with simulated modifications in subtropical high‐pressure systems, low‐level moisture transport, upper‐tropospheric circulation and tropical sea surface temperature warming. While increased rainfall may enhance water availability in some areas, localized drying and increased variability imply persistent climate risks. These findings highlight a strong scenario dependence of future JJAS rainfall over the GHA and underscore the need for improved regional climate modelling to support adaptation planning, water resource management and climate resilience across the GHA.