Land surface feedbacks and palaeomonsoons in northern Africa

We ran a sequence of climate model experiments for 6000 years ago, with land-surface conditions based on a realistic map of palaeovegetation, lakes and wetlands, to quantify the effects of land-surface feedbacks in the Saharan region. Vegetation- induced albedo and moisture flux changes produced year-round warming, forced the monsoon to 17 degrees-25 degrees N two months earlier, and shifted the precipitation belt approximate to 300 km northwards compared to the effects of orbital forcing alone. The addition of lakes and wetlands produced localised changes in evaporation and precipitation, but caused no further extension of the monsoon belt. Diagnostic analyses with biome and continental hydrology models showed that the combined land- surface feedbacks, although substantial, could neither maintain grassland as far north as observed (approximate to 26 degrees N) nor maintain Lake "MegaChad" (330,000 km(2))