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Although desert dunes cover 5 per cent of the global land surface and 30 per cent of Africa, the potential impacts of twenty-first century global warming on desert dune systems are not well understood. The inactive Sahel and southern African dune systems, which developed in multiple arid phases since the last interglacial period, are used today by pastoral and agricultural systems that could be disrupted if climate change alters twenty-first century dune dynamics. Empirical data and model simulations have established that the interplay between dune surface erodibility (determined by vegetation cover and moisture availability) and atmospheric erosivity (determined by wind energy) is critical for dunefield dynamics. This relationship between erodibility and erosivity is susceptible to climate-change impacts. Here we use simulations with three global climate models and a range of emission scenarios to assess the potential future activity of three Kalahari dunefields. We determine monthly values of dune activity by modifying and improving an established dune mobility index so that it can account for global climate model data outputs. We find that, regardless of the emission scenario used, significantly enhanced dune activity is simulated in the southern dunefield by 2039, and in the eastern and northern dunefields by 2069. By 2099 all dunefields are highly dynamic, from northern South Africa to Angola and Zambia. Our results suggest that dunefields are likely to be reactivated (the sand will become significantly exposed and move) as a consequence of twenty-first century climate warming.

As part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest Kalahari, data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces, and that the majority of surface activity occurs on the crests and upper slopes of the dunes. The data suggest that the limiting variables on surface sediment movement vary on different parts of a dune. On interdunes and lower dune slopes the primary limiting variable is available wind energy, while on dune crests and upper slopes it is vegetation cover. Ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation. From individual data points, no evidence is found to support a threshold vegetation cover below which sediment movement occurs. Rather, a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change. However, dunes with differing amounts of mean vegetation cover display differing degrees of surface activity, and at this scale, a vegetation cover threshold in the region of 14 per cent may be recognized.

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