On the dry valleys of the Kalahari: Documentary evidence of environmental change in central southern Africa

Dry 'fossil' valleys (mekgacha) are an important landscape feature in the semi-arid to arid Kalahari Desert of central southern Africa. The majority of valleys do not contain flow, except in their headwater regions, but may contain pools of water on a seasonal basis. As a result, they are frequently mentioned in historical accounts of the region recorded by European travellers, and from these reports it is possible to assemble a picture of hydrological change. This paper describes the evidence for such change, for the period c.1750 until c.1910. Discussion mainly concerns the most frequently observed valleys, the Molopo and Kuruman, although Middle Kalahari systems are also considered. The picture which emerges is one of little change in Middle Kalahari systems. A decline in flow in the Kuruman since c.1750 is tentatively identified, pre-dating the period of permanent human settlement in this region. The river appears to have established its present regime after 1800. A previously unrecognized flood event in the Kuruman in 1820 is also identified. These hydrological changes are placed within the context of historical climate evidence from the southern Cape of South Africa and show close correlation. This suggests that documentary evidence may be used to extend the climate record established for the southern African summer rainfall zone into the Kalahari.