干旱区生态环境知识资源中心

The rise and fall of ancient cultures in drylands is mainly controlled by the availability of water. Where no perennial water sources are available, (ancient) cultures in drylands often depend on the availability of water by effective rainfall as a source for water-harvesting measures. These settlements are susceptible to climatic changes. The reconstruction of such climate-human interactions is constrained, as paleoclimatic proxy archives provide climatic information at most with annual or seasonal resolutions, which is often not a sufficient resolution to relate them to the reactions or adaptations of societies to climatic shifts. For the city of Naga (16 degrees N 33 degrees E) in the dry hinterland of the middle Nile River, we present precipitation data for the last 6500 years employing two different downscaling approaches. In time slice experiments, we simulated selected episodes using a spatially high-resolved atmosphere general circulation model. Furthermore, combining observed precipitation data and a simulation of a coupled ocean-atmosphere general circulation model, we attained statistically downscaled precipitation data for the last 6500 years. Our results indicate that the mean precipitation and the frequency of runoff-generating rainfall events decreased from 6000 until 2000 years B. P. Since then, no significant changes occurred. Thus, the foundation of Naga about 2500 years B. P. coincided with a time when rainfall was still more reliable and less variable. Alterations in orbital parameters (according to Milankovic theory) may have been a major reason for the abandonment of the city.