Representation of Present and Future of Mean and Extreme Precipitation in CMIP6 HighResMIP Simulation over West Africa

This research investigates the representation of present and future of mean and extreme precipitation in the High Resolution Model Intercomparison Project (HighResMIP) within the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations over West Africa. The ensemble means of eight high- and low-resolution simulations, referred to as ENSEMBLE-H and ENSEMBLE-L, were analyzed for the period 2025–2049. Future mean and extreme precipitation patterns were examined for two sub regions of West Africa: the Sahel and the Guinea Coast. Projected annual rainfall peaks at 250 mm/month in May and 150 mm/month in both August and September. The onset of precipitation is expected between the 35th and 67th day of the year for the Guinea Coast, and between the 135th and 165th day for the Sahel. Cessation days are projected between the 315th and 330th day for the Guinea Coast, and between the 250th and 280th day for the Sahel. The length of the growing season is anticipated to increase, reaching around 10 months for the Guinea Coast and 4 months for the Sahel by 2045–2049. High rainfall events are projected to occur in 2035 and 2036, exceeding normal levels. The spatio-temporal analysis of extreme precipitation shows a more significant increase in the highest one-day precipitation over the Sahel (approximately 30%) compared to the Guinea Coast (less than 20%). Additionally, heavy rainfall events (r10mm) are projected to see a positive change of around 8% over the Guinea Coast and 12% over the Sahel. These results suggest potential future re-greening of the Sahel. A greater positive change in precipitation is projected over the Sahel compared to the Guinea Coast during the 2025–2049 period.