![]() ![]() 1b i.e., assuming the changes in precipitation are caused primarily by changes in the position of the ITCZ, not its intensity or the duration of the wet season). Similarly, the simulated mean position of the African ITCZ during boreal summer is shifted by about 1 degree, compared with a minimal shift of about 5 degrees required to maintain a Saharan steppe ( Fig. 1b Jolly et al., 1998 Joussaume et al., 1999) or lacustrine environments (Lézine et al., 2011). However, all models severely underestimate reconstructions of the minimal increase in precipitation required to sustain a Saharan steppe: simulated changes do not exceed 100 mm yr −1 in the mid Sahara, in disagreement with evidence of widespread grasslands that require an increase of at least 200-300 mm yr −1 (Fig. 1a see Harrison et al., 2015 Chevalier et al., 2017 for a detailed analysis). As expected, a clear northward shift of the annual-mean precipitation over Africa is captured in the ensemble mean of PMIP3 models ( Fig. ![]()
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