Using Resolved Jet Dynamics to Address Rainfall Uncertainty over the Sahel

Simulations of 21st century rainfall disagree on whether wetter or drier conditions should be expected over the Sahel. Sea surface temperature (SSTs), aerosols, and greenhouse gases have all been implicated as the primary drivers of the historical rainfall variability. Changes in large-scale dynamics over the Sahel – the strength and position of three zonal jets (AWJ, AEJ, TEJ) – is a key interim step by which this forcing is communicated into changes in rainfall. We report of results showing that jet dynamics from an ensemble of CMIP5 simulations infer a robust increase in future rainfall over the Sahel. Our findings suggest that deficiencies in convective parameterizations or land-atmosphere feedbacks, as opposed to discrepancies in remote forcing, may be causing much of the uncertainty in future projections. We identify a key mode of jet variability and demonstrate how it can be used to reconstruct historical rainfall from fully resolved atmospheric fields. Our approach adds resolution to the complex teleconnection chain delivering rainfall to the Sahel and provides a useful tool to investigate a number of critical open research questions concerning the remote forcing of historical and future rainfall.