The purpose of this study is to perform a high-resolution general circulation model (GCM) experiment to quantify the sensitivity of regional climate to change in vegetation around the Mediterranean basin, corresponding to vegetation change during the Roman Classical Period (RCP), about 2,000 years before present (yr BP). First, and RCP vegetation distribution based on fossil pollen maps and historical records was defined. Second, the RCP vegetation inferred from palynology and other proxies, was converted to the 12 vegetation types required by the biosphere model implemented in the GCM. The albedo change due to the change in vegetation significantly alters the atmospheric circulation over northern Africa and the Mediterranean. The consequences of this change involve a northward shift of the ITCZ over the African continent and a coupled circulation between northwestern Africa and the Mediterranean Sea. A large increase of precipitation occurs over the Sahel, the Nile valley and northwestern Africa. A smaller increase of precipitation occurs also over the Iberian peninsula and the region corresponding to the south of the Caucasus range (Armenia). The increase of precipitation over northern Africa, the Iberian peninsula and the Armenian region are consistent with the pollen, historical and geographical data. The results of this study suggest that deforestation around the Mediterranean during the last 2,000 years may be a major factor in the dryness of the current climate.
Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
last update: 5 January 1998
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