Landscapes rarely reflect any one particular set of environmental conditions (process domain) or period of climate or geological change. Quaternary climate oscillations have left their imprint on desert landscapes such as the Sahara, where it is possible to define two main modes of desert behaviour since the Last Glacial Maximum, around 20 ka ago: an arid mode, dominated by ‘desert’ processes, and a humid mode, dominated by processes usually associated with semi-arid or temperate conditions. As the surface processes vary with the climate regime, so does the nature of the geohazard threat. Some hazards will change in magnitude and frequency as the climate shifts between humid and arid periods (e.g. wadi floods and associated channel erosion, salt aggressiveness), others will no longer be credible because of changes in sediment availability (e.g. stabilization of dunes by vegetation in humid periods) or sediment transport potential (e.g. mega-dunes are essentially stable under relatively weak interglacial wind regimes).

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