Investigating West African Monsoon Features in Warm Years Using the Regional Climate Model RegCM4

Abstract

This study investigates the changes in West African monsoon features during warm years using the Regional Climate Model version 4.5 (RegCM4.5). The analysis uses 30 years of datasets of rainfall, surface temperature and wind parameters (from 1980 to 2009). We performed a simulation at a spatial resolution of 50 km with the RegCM4.5 model driven by ERA-Interim reanalysis. The rainfall amount is weaker over the Sahel (western and central) and the Guinea region for the warmest years compared to the coldest ones. The analysis of heat fluxes show that the sensible (latent) heat flux is stronger (weaker) during the warmest (coldest) years. When considering the rainfall events, there is a decrease of the number of rainy days over the Guinea Coast (in the South of Cote d’Ivoire, of Ghana and of Benin) and the western and eastern Sahel during warm years. The maximum length of consecutive wet days decreases over the western and eastern Sahel, while the consecutive dry days increase mainly over the Sahel band during the warm years. The percentage of very warm days and warm nights increase mainly over the Sahel domain and the Guinea region. The model also simulates an increase of the warm spell duration index in the whole Sahel domain and over the Guinea Coast in warm years. The analysis of the wind dynamic exhibits during warm years a weakening of the monsoon flow in the lower levels, a strengthening in the magnitude of the African Easterly Jet (AEJ) in the mid-troposphere and a slight increase of the Tropical Easterly Jet (TEJ) in the upper levels of the atmosphere during warm years.

Rainfall Variability and Trends over the African Continent Using TAMSAT Data (1983–2020): Towards Climate Change Resilience and Adaptation

“…However, Africa receives rainfall over two major monsoons: The West African monsoon (WAM) and the East African monsoon (EAM). During the WAM, winds blow southwest from the North Atlantic Ocean, keeping the Inter-Tropical Convergence Zone (ITCZ) above the equator, and WAM usually occurs from June to September [26,27]. West African Sahel became known as having the region's most devastating drought because of changes in WAM conditions during the 1970s and 1980s [28,29].…”

Late 21st Century Projected Changes in the Relationship between Precipitation, African Easterly Jet, and African Easterly Waves

“…More recently, there have been remarkable efforts to improve our understanding of the West African climate system using a regional climate modeling approach [28][29][30][31][32][33][34][35]. For instance, a number of projects have been developed to advance the understanding of the WAM system [31][32][33][34][35] and to comparatively assess the modeling of the WAM mean climatology and its projected changes [29,36,37]. Such studies are based on the physical understanding of the monsoon system, along with its variability and rely mostly on the ability of regional climate models to accurately represent large-scale circulation features [3,16,17,19,[38][39][40].…”

“…In fact, a limited number of studies have attempted to investigate the relationship between changes in WAM features and precipitation changes [16,17,19,22,36,38,[40][41][42][43]. In this study, we utilize an unprecedented high-resolution regional climate model RegCM4 simulations over the West Africa domain under two Representative Concentration Pathways (RCP4.5 and RCP8.5) in the late 21st century to investigate the relationship between the AEJ, the AEWs, the convection, and summer monsoon precipitation changes.…”