Do climate models agree on seasonal rainfall patterns and future changes over southern Africa?

Understanding how rainfall will change over the southern Africa is a challenge, in part, due to large uncertainties in climate model projections. Using a large set of 201 global climate model simulations from the Coupled Model Intercomparison Project Phases 5 and 6 (CMIP5 and CMIP6) and 2018 UK Climate Projections (UKCP18), this study provides an in-depth investigation into future changes in southern African precipitation. Specifically, the spatial and temporal variation of model agreement, the intra- and inter-model uncertainties and the roles of interdecadal variability are examined. Model projections show agreement on drying over most of southern Africa in the dry season and the onset of the rainy season. Meanwhile in the main rainfall season, there is less agreement between models regarding the direction and magnitude of change over much of southern Africa, including in Zimbabwe, Mozambique, Zambia and Malawi. The range in future projections is not linked with biases in the historical climatology, and intra-model uncertainty analysis shows that multiple simulations of the same model often produce disagreeing projections in the sign of precipitation change when compared to the historical period. This highlights the importance of internal variability in influencing rainfall projections over southern Africa. For many models, this substantial interdecadal variability is greater than the projected future change. Given the large variability and uncertainty in models over southern Africa, impact and adaptation studies should consider the strong probability of both wet and dry years, and wet and dry decades, in the future.