Abstract
AbstractThe 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.
Highlights
West African monsoon (WAM) prevails during the West African rainy season and provides a large amount of rainfall, over 75% (Hagos and Cook 2007), in most parts of the region
This study examined the impacts of global warming on precipitation amount during the West African monsoon season using the pseudo-global warming (PGW) method
The estimated rainfall amount in the 2070s from the PGW runs increased slightly compared with the current climate runs
Summary
West African monsoon (WAM) prevails during the West African rainy season and provides a large amount of rainfall, over 75% (Hagos and Cook 2007), in most parts of the region. Coupled global circulation models (GCMs) are useful tools for performing global simulations These state-of-the-art models can be employed to investigate climate change associated with increase in greenhouse gas concentrations caused by anthropogenic activities. The coarse nature of GCM’s horizontal resolution limits their ability to reproduce local climates, which are directly related to the inability of the model to properly resolve orographic features (IPCC 2007). Other methods such as statistical downscaling (Schmidli et al 2006), dynamical downscaling (CORDEX, Giorgi et al 2009), and direct simulation by high-resolution GCM (Wild et al 1995) are gaining more application to project climate conditions at a regional scale. A grid point interval of less than several kilometers or rather at a convection-permitting scale, usually less than 4 km (Prein et al 2013), is more appropriate for simulating the complex interactions related to orography and local climate, which directly impact the monsoon system of the region
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