Dunefield activity response to climate variability in the southwest Kalahari

Aeolian activity on the crests of linear dunes in the arid southwest Kalahari Desert is primarily controlled by vegetation cover. Cover is temporally variable in response to rainfall, with mobility index (MI) values and field based studies demonstrating the dynamic nature of aeolian processes in this dunefield. Landsat TM data for a drought (1984) and wetter (1993) year were analysed for two subscenes in the dune field, one for a pastoral landscape and one for a conservation area, to investigate the spatial dynamics of dune activity, using the empirically determined 14% cover threshold as the limit to crestal aeolian activity. TM band 3 data were found to best represent vegetation cover, including senesced material, at the end of the dry season, the period when the potential for aeolian activity is normally high due to the wind strength at this time. The extent of 0-14% cover areas ranged from 10% (1984) to 3% (1993) for the pastoral area and 16% (1984) to 6% (1993) for the conservation landscape. The wetter (1993) image residuals have different spatial characteristics in the two subscenes, with bare active dunes in the pastoral lands associated with locations of livestock pressure and those in the conservation area related to natural fire events. The study demonstrates the spatial dynamics of temporally variable linear dune activity in the southwest Kalahari, and also shows that areas devegetated by drought can recover sufficient vegetation in wet years to limit the spatial extent of aeolian transport on dune crests.