Impacts of Global Warming on West African Monsoon Rainfall

Abstract

The impacts of global warming on rainfall in West Africa were examined using a numerical framework for 5 monsoon years (2001, 2007, 2008, 2010, and 2011). Rainfall characteristics over the three climatic zones, Guinea coast, Savannah, and Sahel, were analyzed. The potential changes associated with global warming were 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 Tropical Rainfall Measuring Mission and Global Precipitation Climatology Project rainfall alongside surface temperature from the European Center for Medium-Range Weather Forecast Reanalysis. Results show that the estimated rainfall amount from the future climate in the 2070s increases slightly compared with the current climate. The total rainfall amount simulated for the current climate is 16% and 63% less than that of the PGW runs and observations, respectively. Also found is an increase (decrease) in heavy (light and moderate) rainfall amount in the PGW runs. These results are, however, contingent on the global circulation model (GCM), which provides the boundary conditions of the regional climate model. CESM1.0-CAM5.2, the GCM employed in this study, tends to provide a greater surface temperature change of about 4 C. This projected temperature change consequently caused the increase in the simulated precipitation in the PGW experiments, thus highlighting the advantage of using the PGW method to estimate the likely difference between the present and future climate with reduced large-scale model differences and computational resources. The findings of this study are, however, useful to inform decision-making in climate-related activities and guide the design of climate change adaptation projects for the West African region.