Projections of a Wetter Sahel in the 21st Century from Global and Regional Models

Confident regional-scale climate change predictions for Africa are needed to support adaptation planning. State-of-the-art regional climate model simulations at 90-km and 30-km resolution are run and analyzed along with output from CMIP5 AOGCMs to predict how the West African and Sahel summer surface temperature, precipitation, and surface moisture are likely to change at mid- and late-century due to increased atmospheric CO2 concentrations under the RCP 8.5 emission scenario and evaluate confidence in such projections.

It is shown that the regional climate model can realistically simulate the current summer evolution of the West Africa monsoon climate including the onset and demise of the Sahel wet season, a necessary but not sufficient condition for confident prediction.

RCM and AOGCM projections indicate the likelihood for increased surface air temperatures over this century, with Sahara and Sahel temperature increases of 2 – 3.5 K by mid-century, and 3 – 6 K by late-century. Summer rainfall and surface moisture are also projected to increase over most of the Sahel. This is primarily associated with an increase in rainfall intensity and not a lengthening of the wet season. Pinpointing exactly when the rainfall and surface moisture increase will first commence and by exactly what magnitude is less certain as these predictions appear to be model dependent. Models that simulate stronger warming over the Sahara are associated with larger and earlier rainfall increases over the Sahel due to an intensification low-level West African westerly jet, and vice versa.