The Role of the Atlantic Meridional Overturning Circulation in the Projection of Sahel Precipitation

The Atlantic Meridional Overturning Circulation (AMOC) is widely anticipated to weaken by the end of the 21^st century, although there is considerable disparity among state-of-the-art Earth System Models (ESM) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) regarding the magnitude of this weakening. Notably, the weakening of AMOC has been shown to influence future precipitation patterns over different regions, including across West Africa. Uncertainty in projections of Sahel precipitation has persisted across generations of ESM and remains a significant challenge for stakeholders. Towards the end of the 21st century, many climate models predict a dipole pattern, characterized by a drought across western Sahel and an increased rainfall across the central Sahel.

Recent work has shown that models displaying this zonal dipole pattern tend to predict a southward shift in the position of the Atlantic Intertropical Convergence Zone (ITCZ), while those that do not show this dipole tend to predict a northward shift in the Atlantic ITCZ. Furthermore, for the models that do produce this dipole, variability in the longitude where drying transitions to increased precipitation remains difficult to explain. In this study, we seek to elucidate the relationship between changes in AMOC and changes in Sahel precipitation, particularly exploring the potential influence of AMOC on the Atlantic ITCZ and its connection with zonal variability across the Sahel. We use an ensemble of CMIP6 models and statistical analysis to connect the weakening of the AMOC to structural changes in Sahel precipitation across models. Finally, we explore potential mechanisms, including changes to the subtropical high, that may connect these critical climate signals.