Investigating the influence of Fouta Jallon topography on the West African mean surface climate using RegCM5

This study uses the International Center for Theoretical Physics (ICTP) Regional Climate Model version 5 (RegCM5.0) to investigate the impact of the Fouta Djallon topography on the mean surface climate of West Africa with a focus on the June–September (JJAS) season. Two experiments were conducted: a control simulation with current topography (REF) and a sensitivity simulation with flattened terrain (FLAT). Results show that reducing the elevation leads to decreased rainfall and increased temperatures, particularly over the Guinea Coast and the modified topographic region. Rainfall decreases by approximately 4.59% in the Guinea Coast sub-zone, while it slightly increases by about 2.76% in the Sahel. The most significant rainfall reduction, exceeding 20%, occurs over the flattened area. Temperature rises across both regions, with the strongest warming over the Fouta Jallon region. This pattern is likely due to the suppression of orographic uplift, which enhances the southwesterly monsoon flow from the Atlantic Ocean and causes a northward shift of the Intertropical Convergence Zone (ITCZ) into the Sahel. The findings highlight the key role of Fouta Jallon topography on the West African climate system.