Projection of West African summer monsoon rainfall in dynamically downscaled CMIP5 models
West Africa faces an increasing challenge related to water resources in the coming decades; hence high-confidence climate projection is crucial for the region’s future. In this study, future changes in summer monsoon rainfall under the RCP8.5 scenario were investigated over West Africa for the period of 2074–2099 with respect to the present-day period of 1980–2005 using the Rossby Centre Regional Climate Model (RCA4), driven by six Coupled Model Intercomparison Project phase 5 (CMIP5) global circulation models (GCMs). Through evaluation of the present climate, the RCA4 simulations and their multi-model ensemble mean (EnsMean) reasonably reproduced the climatology of the summer rainfall and associated tropospheric circulation features. In a warmer climate, summer monsoon rainfall is projected to increase in most parts of West Africa, but a decrease is expected in the northwest, around Senegal. Changes in the monsoon circulation are opposite in the lower and upper troposphere, with the tipping point at 400 hPa. Specifically, a projected strengthening and northward shift is observed at the lower and mid-tropospheric level, while weakening is evident at the upper tropospheric level. A diagnosis based on a moisture budget equation reveals that the robust positive response of West African summer monsoon rainfall to global warming is largely explained by the enhancement of moisture convergence and surface evaporation.
KeywordsMonsoon Global warming Climate change Dynamical downscaling African easterly jet Tropical easterly jet
This work is supported by National Nature Science Foundation of China Grant (41675062), and Research Grants Council of the Hong Kong Special Administrative Region, China (CityU 11305715 and 11335316). The first author is a recipient of a research studentship provided by the City University of Hong Kong (CityU). The authors appreciate WCRP and START for setting up and funding the CORDEX-Africa analysis initiative, and the University of Cape Town for leading the training and analysis program. We are very grateful to the regional downscaling group who kindly shared the downscaled data used in this analysis. We are also grateful to the services that have operated the CMIP5 GCMs, GPCP, CRU, and NCEP/NCAR datasets. We thank the anonymous reviewers for their constructive comments and suggestions.
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