Relationship between the Future Projections of Sahel Rainfall and the Simulation Biases of Present South Asian and Western North Pacific Rainfall in Summer

Confident model projections of regional climate, in particular precipitation, could be very useful for designing climate change adaptation, particularly for vulnerable regions such as the Sahel. However, there is an extremely large uncertainty in the future Sahel rainfall projections made by current climate models. In this study, we find a close relationship between the future Sahel rainfall projections and present rainfall simulation biases in South Asia and the western North Pacific in summer, using the historical simulations and future projections of phase 5 of the Coupled Model Intercomparison Project (CMIP5). This future-present relationship can be used to calibrate Sahel rainfall projections since historical simulation biases can be much more reliably estimated than future change. The accordingly calibrated results show a substantial increase in both precipitation and precipitation minus evaporation in the future Sahel, in comparison with the multimodel ensemble (MME) result. This relationship between the historical rainfall bias and future Sahel rainfall projection is suggested to lie with the different schemes of convective parameterization among models: some schemes tend to result in both overestimated (underestimated) historical rainfall in South Asia (the western North Pacific) and enhanced future Sahel rainfall projection, while other schemes result in the opposite.