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The results of the interdisciplinary project ACACIA support the assumption of a more humid climate at Djara, on the Egyptian Limestone Plateau, which is a hyper-arid desert today, during the early and mid-Holocene. The ancient plant and animal inventories give new impetus for the suggestion of an interfingering of two climatic regimes, the winter rains from the north and west and the summer monsoonal rains from the south, on the latitude of Djara. A playa sediment sequence, the composition of plant and animal taxa as well as the reconstructed settlement patterns indicate a semi-arid climate with alternating more humid and drier conditions.

The concentration of prehistoric sites in the Djara depression points to locally favourable conditions in contrast to the surrounding plateau surface. The widespread catchment and a distinct system of palaeochannels offered fresh water over a period of time due to the run-off from the plateau surface after rain events. Although the ecological conditions were better during the Holocene humid phase than they are today, a sedentary way of life was improbable. The hydrological constraints require altogether highly mobile subsistence strategies. Shells of the Nile bivalve Aspatharia sp. (Spathopsis sp.) give evidence for contacts between Djara and the Nile Valley, which remains beside the Egyptian oases an important retreat area with perennially available water. The decrease of radiocarbon dates and related archaeological sites around 6300 BP (c. 5300 cal BC) indicate the depopulation of the Djara region as a consequence of the drying trend. While the drop off of the C-14-dates can also be observed in other desert research areas of the ACACIA-project, we date the end of the Holocene humid phase about 300 years earlier than previously suggested. (c) 2006 Elsevier Ltd. All rights reserved.