Pollen evidence indicates that grassland and xerophytic woodland/scrubland occurred in ares of northern Africa characterised by desert today during the mid-Holocene (Jolly et al., 1998a, 1998b). Mid-Holocene pollen assemblages for sites south of 23° N do not contain taxa with desert affinities (Dominique Jolly, unpublished analyses), indicating that the region south of 23° N was characterised by grassland not desert.
The increase in mean annual precipitation required to support grassland at each latitude from 0 to 30° N compared to the modern precipitation at that latitude, zonally averaged over the range 20° W to 30° E longitude, has been calculated using the water-balance module from the BIOME3 equilibrium vegetation model (Haxeltine and Prentice, 1996) (see Joussaume et al., 1999). The latitudinal distribution of biomes (reconstructed at individual pollen sites) in northern Africa today and during the mid-Holocene (6000 ±500 yr B.P.) are shown on the graphic below. The grey-shaded area on the graphic shows maximum and minimum estimates of the increase in precipitation required to support grassland at each latitude. To use this graphic as a model benchmark, simulated DeltaP is required to lie above/within the grey band at all latitudes from 0-23° N.
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If you wish to use these data as a diagnostic, please cite Joussaume et al. (1999) as the first application, and the following website http://www.bridge.bris.ac.uk/pmip2/synth/index.htm as the source.