On the Coherence of Sahel Region under Different Emissions Scenarios

The interannual variability of precipitation over Africa in summer is dominated by the Sahel region that expands from west to east on the southern border of the Sahara Desert. Any subregion in the Sahel is highly correlated with the region mean indicating that the region is homogeneous with respect to interannual rainfall variability, and that this variability is characterized by a dominant mode for the entire region superimposed by weaker local changes in the subregions. In this work, we test the coherence of the Sahel region under different emissions scenarios using precipitation from the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) dataset. The NEX-GDDP dataset includes downscaled projections for RCP 4.5 and RCP 8.5 from 21 CMIP5 models. Some models capture the precipitation signal over the Sahel in summer while other models miss the spatial patterns by dividing the Sahel into smaller regions with dissimilar interannual variability, generating random spatial patterns, or simulating Sahel-like precipitation variability shifted in space. This regionalization analysis provides a method for interpreting simulations properly when studying climate process or projecting climate change impacts. If a model has systematic spatial shifts of the Sahel climate pattern, then analysis of Sahel sensitivity in this model should be performed with a corresponding shift. This opens the possibility of a more meaningful, regionalization-based multi-model ensemble of climate projections for the Sahel. In the long term, these studies can also inform model development to correct spatial biases and displacements in the representation of climate variability.