Abstract
Drylands are home to over 2 billion people globally, many of whom use the land for agricultural and pastoral activities. These vulnerable livelihoods could be disrupted if desert dunefields become more active in response to climate and land use change. Despite increasing knowledge about the role that wind, moisture availability and vegetation cover play in shaping dryland landscapes, relatively little is known about how drylands might respond to climatic and population pressures over the 21st century. Here we use a newly developed numerical model, which fully couples vegetation and sediment-transport dynamics, to simulate potential landscape evolution at three locations in the Kalahari Desert, under two future emissions scenarios: stabilising (RCP 4.5) and high (RCP 8.5). Our simulations suggest that whilst our study sites will experience some climatically-induced landscape change, the impacts of climate change alone on vegetation cover and sediment mobility may be relatively small. However, human activity could strongly exacerbate certain landscape trajectories. Fire frequency has a primary impact on vegetation cover, and, together with grazing pressure, plays a significant role in modulating shrub encroachment and ensuing land degradation processes. Appropriate land management strategies must be implemented across the Kalahari Desert to avoid severe environmental and socio-economic consequences over the coming decades.
Highlights
Dryland environments are extreme in their nature, typified by non-equilibrium conditions in climate, vegetation and geomorphology[1,2,3]
Whilst large-scale vegetation shifts are known to result from variations in external forcing[26], the potential impacts of 21st century climatic change on dryland vegetation cover and composition remain unclear[27]
We explore the potential impacts of climate change and human land management on landscape processes in the Kalahari Desert in southern Africa
Summary
The current climate of southern Africa is characterised by marked interannual and interdecadal variability[43], due to influence from both tropical and mid-latitude climate systems[44]. At Maun, proportional tree cover generally increases during both wet and dry seasons as the century progresses, in low-variability scenarios (Fig. 3m,n). Tshane experiences increased sediment movement throughout the century (Fig. 3u,v), under RCP 8.5, despite an increase in general vegetation cover This is attributed to greater shrub encroachment during this period, since porous shrubs tend to provide less extensive sheltering effects than the bluff bodies of grasses[49]. At Maun, vegetation population density generally declines as the century progresses under both RCPs (Fig. 4a), with simultaneous trends of increasing sediment movement (Fig. 4d) and decreasing shrub dominance (Fig. 4g). Sediment movement at Tshane remains broadly stable throughout the century (Fig. 4e), whilst at Tsabong sediment movement tends to be highest in the first half of the century (Fig. 4f)
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