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Projected robust shift of climate zones over West Africa in response to anthropogenic climate change for the late 21st century


The response of West African climate zones to anthropogenic climate change during the late 21st century is investigated using the revised Thornthwaite climate classification applied to ensembles of CMIP5, CORDEX, and higher-resolution RegCM4 experiments (HIRES). The ensembles reproduce fairly well the observed climate zones, although with some notable discrepancies. CORDEX and HIRES provide realistic fine-scale information which enhances that from the coarser-scale CMIP5, especially in the Gulf of Guinea encompassing marked landcover and topography gradients. The late 21st century projections reveal an extension of torrid climates throughout West Africa. In addition, the Sahel, predominantly semi-arid in present-day conditions, is projected to face moderately persistent future arid climate. Similarly, the Gulf of Guinea shows a tendency in the future to experience highly seasonal semi-arid conditions. Finally, wet and moist regions with an extreme seasonality around orographic zones become less extensive under future climate change. Consequently, West Africa evolves towards increasingly torrid, arid and semi-arid regimes with the recession of moist and wet zones mostly because of the temperature forcing, although precipitation can be locally an important factor. These features are common to all multimodel ensembles, a sign of robustness, with few disagreements in their areal extents, and with more pronounced changes in the higher-resolution RCM projections. Such changes point towards an increased risk of water stress for managed and unmanaged ecosystems, and thus add an element of vulnerability to future anthropogenic climate change for West African water management, ecosystem services and agricultural activities.

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This work is supported by the German Federal Ministry of Education and Research through the West African Science Service Center on Climate Change and Adapted Landuse (WASCAL); and the United States Agency for International Development (USAID) through Partnerships for Enhanced Engagement in Research (PEER Project 2–344). The computation for the HIRES simulations was done at the Abdus Salam International Centre for Theoretical Physics (ICTP, Trieste, Italy). Therefore we would like to thank the Earth System Physics section for their support. We are also grateful to the CMIP5 and CORDEX modeling centers and the anonymous reviewers whose comments have improved the quality of this paper.

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Correspondence to Mouhamadou Bamba Sylla.

Electronic supplementary material

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Figure S1

Distribution of reference period thermal types using PE from the Thornthwaite (left panels) and Hamon (right panels) methods for UDEL (a and b) and CRU (c and d) (PDF 280 kb)

Figure S2

Distribution of reference period thermal types using PE from the Thornthwaite (left panels) and Hamon (right panels) methods for CRU (a and b), CMIP5 (c and d), CORDEX (e and f) and HIRES (g and h) ensembles using all models (PDF 274 kb)

Figure S3

Same as Fig. 2 but for the moisture types (PDF 302 kb)

Figure S4

Distribution of thermal types for reference period (left panels), future RCP4.5 (middle panels) and future RCP8.5 (right panels) for the CMIP5 (a, b and c), CORDEX (d, e and f) and HIRES (g, h and I) ensembles using all models (PDF 294 kb)

Figure S5

Same as Fig. 4 but for the moisture types (PDF 357 kb)

Figure S6

Distribution of climate types for reference period (1975-2004; left panels), future RCP4.5 (2080-2099; middle panels) and future RCP8.5 (2080-2099; right panels) for the CMIP5 (a, b and c), CORDEX (d, e and f) and HIRES (g, h and I) ensembles using the 3 GCMs that drive HIRES. Abbreviations definition: T: Torrid; H: Hot; W: Warm; Cl: Cool; Cd: cold; F: Frigid (PDF 645 kb)

Figure S7

Same as Fig. 6 but for the ensembles of 8 CMIP5 GCMs that force CORDEX, CORDEX and HIRES (PDF 640 kb)

Figure S8

Changes (RCP4.5/8.5 minus reference period) in moisture index and superimposed ratio between change in precipitation (in %) and change in PE (in %) for CMIP5 (a and b), CORDEX (c and d) and HIRES (e and f) ensembles using all models (PDF 460 kb)

Figure S9

Distribution of reference period seasonality for UDEL (a), CRU (b), CMIP5 (c), CORDEX (d), and HIRES (e) ensembles using all models. The “dots” (.) is for seasonality caused by temperature, the “stars” (*) for seasonality caused by both temperature and precipitation and the “plus” (+) for seasonality caused by precipitation (PDF 264 kb)

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Sylla, M.B., Elguindi, N., Giorgi, F. et al. Projected robust shift of climate zones over West Africa in response to anthropogenic climate change for the late 21st century. Climatic Change 134, 241–253 (2016).

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  • Couple Model Intercomparison Project Phase
  • Areal Extent
  • Ensemble Size
  • Climate Type
  • Anthropogenic Climate Change