Sonja van Renssen
Climate change is likely to “activate” sand dunes across Southern Africa , with potentially disastrous consequences, report researchers in the journal Nature. As the Kalahari desert gets hotter and drier in the 21st century, dunes will become unstable and vegetation for grazing scarce.
Three global warming scenarios, representing the current range of climate change predictions, modelled what would happen to the dunes in the coming century. “By 2070, the models all predict a significant increase in dune activity,” says David Thomas of the University of Oxford, United Kingdom.
Dune activity depends on two main factors: soil moisture and wind. With little moisture and high winds, vegetation declines, allowing sand to be picked up and blown around. The higher temperatures caused by global warming will lead to a long-term decline in soil moisture, longer and more frequent droughts and stronger winds, say the researchers.
They say the expected loss of vegetation could be disastrous for pastoral farmers, whose livestock depend on plants for grazing. “It’s going to be a lot harder to keep livestock alive and, therefore, harder for people to live on a sedentary basis in large parts of the Kalahari,” says Thomas. He foresees a possible return to the nomadic lifestyle that was the norm before large-scale pastoral farming.
The Kalahari is an immense region of arid and semi-arid land, covering about 70% of and parts of Angola, Namibia, South Africa, Zambia and Zimbabwe.
The research predicts that by 2040 the southern dunes of and will be “activated”; by 2070, the more northern and eastern dunes of Angola, Zambia and Zimbabwe; by 2099, all the dunes from Angola and Zambia in the north to those in South Africa.
Some climate models do forecast a seasonal increase in rainfall, but even these conclude that benefits would be wiped out by increased evaporation because of higher air temperatures.
Enhanced levels of carbon dioxide, which in theory could stimulate plant growth, are unlikely to have much positive impact in practice. Extra carbon dioxide helps “only if the plants are not stressed, which they will be if there’s a moisture deficit,” says Thomas.
The potential for human activities to affect the shifting dunes should not be underestimated, says David Niemeijer, co-author of a recent report on desertification published by the Millennium Ecosystem Assessment. “Conserving water and planting trees could make things better,” he says, “or improper husbandry could make things worse.” Recent decades have also seen an unprecedented intensification of grazing that has led to local desertification. -- Scidev.net