Abstract:
A set of numerical experiments was conducted in order to investigate the impacts of global
warming on West African monsoon rainfall for selected five years. The experiments varied different
cumulus, microphysics and planetary boundary layer parameterization schemes. Rainfall characteristics
over three climatic zones, Guinea Coast, Savannah and Sahel, was analyzed. The potential change
associated with global warming is assessed by the pseudo global warming (PGW) downscaling method.
Multiple PGW runs were conducted using climate perturbation from the 40-member ensemble of the
Community Earth System Model version 1 (CESM1) coupled with Community Atmospheric Model
version 5.2 (CAM5.2) component large ensemble project. The model output was compared with TRMM
and GPCP rainfall and atmospheric parameters from ECMWF reanalysis datasets. Results show that the
rainfall amount in the 2070s estimated from the PGW runs substantially increases, especially in the eastern
Sahel due to enhanced moisture convergence, compared to the current climate. The percentage change in
simulated total rainfall amount can increase or decrease by 50% in the PGW runs and the theoretical
rainfall computed based on Clausius-Clapeyron relation. Also, found is an increase (decrease) in heavy
(both light and moderate) rainfall amount. These results, however, depend on the GCM used as the
boundary conditions of the RCM. This suggests that the 4 o C change in average surface temperature
derived from the 40-member ensemble model strongly influenced the increased rainfall simulated by the
PGW experiments. Thus, highlighting the advantage of using the PGW technique to estimate the likely
difference between present and future climate with reduced large-scale model biases and computational
resources.
