This research focuses on evaluating the High-Resolution Model Intercomparison Project (HighResMIP) simulations within the framework of the Coupled Model Intercomparison Project (CMIP) Phase 6 (CMIP6). We used seven of its consortiums to study how CMIP6 reproduced the West African precipitation features during the 1950–2014 historical simulation periods. The rainfall event was studied for two sub-regions of West Africa, the Sahel and the Guinea Coast. Precipitation datasets from the Climate Research Unit (CRU) TS v4.03, University of Delaware (UDEL) v5.01, and Global Precipitation Climatology Centre (GPCC) were used as observational references with the aim of accounting for uncertainty. The observed annual peak during August, which is greater than 200, 25, and 100 mm/month in the Guinea Coast, the Sahel, and West Africa as a whole, respectively, appears to be slightly underestimated by some of the models and the ensemble mean, although all the models captured the general rainfall pattern. Global climate models (GCMs) and the ensemble mean reproduced the spatial daily pattern of precipitation in the monsoon season (from June to September) over West Africa, with a high correlation coefficient exceeding 0.8 for the mean field and a relatively lower correlation coefficient for extreme events. Individual models, such as IPSL and ECMWF, tend to show high performance, but the ensemble mean appears to outperform all other models in reproducing West African precipitation features. The result from this study shows that merely improving the horizontal resolution may not remove biases from CMIP6.

This study evaluated the performance of seven CMIP6 HighResMIP models in the simulations of drought over two sub-regions of West Africa: the Guinea coast and the Sahel during the historical period of 1985–2014, in terms of the potential evapotranspiration index (PET), climatic water availability (CWA), and standardized precipitation evapotranspiration index (SPEI) at three time scales (i.e., 1, 3, and 12 months). The Climate Research Unit (CRU) TS v4.03 datasets were used as the observation reference. The observation shows that the PET and CWA during August (i.e., the rainfall annual peak) were less than 30 and 200 mm/month over the Guinea coast, respectively. The corresponding values over the Sahel were 100 and -50 mm/month, respectively. A significant decreasing trend was observed in drought over the Guinea coast (except Nigeria) and the Sahel. The frequencies of extreme and severe droughts were observed over Nigeria, Liberia, and Sierra Leone during the historical period. The seven HighResMIP models show different behaviors in simulating all of the abovementioned observation features. Among all the simulations, the ENSEMBLE, ECMWF, and IPSL generally perform better in almost all the statistical indices used, although there are still biases that need to be resolved in the models.