Climate change at the end of the Old Kingdom in Egypt around 4200 BP: New geoarchaeological evidence

The paper presents compilation of geological and geoarchaeological data, based on excavations at the Saqqara necropolis, to denote climate variability in Egypt during the late Old Kingdom (around 2200 BC). A change in climate in that time was expressed firstly by aridification and low floods of the Nile, but also by occasional heavy rainfalls in northern Egypt. Low Nile floods were probably a consequence of decreased summer precipitation in the Ethiopian Highlands that resulted in catastrophically low discharges into the Blue Nile drainage basin. These weaker summer monsoons in Ethiopia and gradual aridification in Egypt that started about 5000 cal BP, were coincident with a southward progressing shifting of the summer Intertropical Convergence Zone in Africa. Simultaneous intensive rainfalls resulted in wide-spread sheet-flood accumulations, attested by archaeological evidence in northern Egypt. These rainfalls could be triggered by the North Atlantic Oscillation. Both these reasons caused a rapid collapse of the Old Kingdom at about 4200 cal BP.