The influence of quasi-biennial oscillation on West African Rainfall

The quasi-biennial oscillation (QBO) is a global climate phenomenon of repeating cycles of tropical stratosphere winds, reversing direction from eastward to westward roughly every 14 months. However, unlike in Eastern Africa and India where QBO effect has been well studied, knowledge about its influence on West African rainfall and its variability is very scares. Using the five historical Coupled Models Intercomparison Project Phase 5 (CMIP5) simulations, (CMCC-CMS, HadGEM2-CC, HadGEM3-A, MPI-ESM-MR and MIROC-ESM-MR), this study investigates the influence of (QBO) on West African precipitation. The capability of the CMIP5 models to reproduce the quasi-biennial oscillation structure was evaluated while the influence of the QBO on West African precipitation was studied using wavelet analysis over the three zones of the regions (Sahel, Savannah, Guinea). Further, we studied the composite of rainfall variability during QBO and non-QBO years and also applied the composite of the QBO to investigate the dominant impacts of its phases (west and east) over the region. Results show that all models capture the general structure of the QBO well with varying biases but HadGEM2-CC produced results closest to observation (ERAINT). Therefore using this model with ERAINT and applying wavelet coherence analysis it was found that there is good coupling between QBO and precipitation over all three climatic zones of West Africa with the coherence of 0.6–0.8 in both ERA-Interim and HadGEM2-CC for the intra-annual (0.5–1.0 year) and inter-annual (2.0–4.0 years) timescales in all zones and at the two levels (30 and 50 hPa) considered. In addition, rainfall rates were found to be generally higher everywhere during the west phase of a QBO year than during the east phase but more so over the Savannah and Guinea region.