Evaluation of extreme precipitation indices over West Africa in CMIP6 models

In this study, the performance of sixteen Coupled Model Intercomparison Project Phase 6 (CMIP6) models in simulating extreme precipitation indices over West Africa has been evaluated. Nine extreme precipitation indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI) have been used. The performance of CMIP6 models and their ensemble mean was examined by comparing the model results to that of Global Precipitation Climatology Project One-Degree Daily Dataset (GPCP) and Tropical Rainfall Measuring Mission Multi-satellite Precipitation Analysis 3B42 (TRMM) gridded observations during the present-day period 1997-2014 with focus on the summer months (i.e., June-July-August, JJA). Our results show that CMIP6 models reasonably reproduce the spatial patterns of the extreme precipitation indices over the entire region, although their performance is quite different between Sahel and Guinea coast subregions. The gridded observations exhibit significant differences in their estimates of the indices evaluated, and the CMIP6 models are generally closer to GPCP than to TRMM. The models broadly exhibit too many consecutive wet days (CWD) resulting in widespread overestimation over entire West Africa. Also, the heavy (R10 mm) and very heavy (R20 mm) precipitation days are considerably overestimated especially over the mountain regions. Overall, the ensemble mean outperforms any individual model at capturing mean distributions of the extreme precipitation indices, particularly in comparison to the two gridded observations.