JOHANNESBURG, South Africa — Global warming
could have a major impact on Africa's southern sand dune systems, spreading
desert-like conditions and destroying the livelihoods of hundreds of thousands
of people before the end of the century, new research warns.
Large parts of interior southern Africa stretching from northern South Africa to
Angola, Zambia and beyond are made up of stabilized sand dunes. They are at
least partially covered in vegetation and support a growing population of
herders and farmers.
But research presented in the June edition of Nature predicts widespread
reactivation of these dunes as average rainfall declines, droughts increase and
wind strengths pick up in the coming decades -- something last seen
14,000-16,000 years ago.
The research is published as British Prime Minister Tony Blair is trying to
persuade leaders of the Group of Eight richest countries to recognize the
science of climate change -- that carbon emissions are causing global warming
with potentially devastating effects in some of the world's poorest countries.
The study conducted by British-based researchers David Thomas, Giles Wiggs and
Melanie Knight considered a number of different climate and emissions scenarios.
"By the time you get to 2070, regardless of the model used, you get a
landscape that is more desert-like than today," Thomas said in a telephone
interview. "Life will potentially be very difficult."
The movement of dunes is driven by two key environmental factors: wind strength
and the dunes' susceptibility to erosion, which in turn is influenced by the
level of rain fall and vegetation cover.
Based on observed dune activity over 20 years of fieldwork in the Kalahari
region, the team was able to simulate how three dune fields would respond to
different climate scenarios and a range of possible emission levels, Thomas
said.
There are widespread predictions that the coming decades will see increased
drought and wind in this region, accompanied by an overall decline in rainfall,
though punctuated with incidents of extreme rainfall in some areas.
But even if moisture levels increase, it will be balanced by heightened
evaporation as temperatures get warmer, and the dune fields will progressively
become exposed and start moving, Thomas argued.
The researchers predict this would happen first -- possibly as soon as 2039 --
in the southern, driest areas and spread progressively northward, reaching into
northern Botswana, eastern Namibia and western Zimbabwe and western Zambia by
2069.
The southern dune field has only partial vegetation cover and has already
experienced temporary local reactivation during recent droughts. But what the
research suggests is different, Thomas said.
"It is region-wide expansion of dune activity, with a long lasting drying
and enhanced sand transport in windy months. As the land dries out, so plants
die ... and then the wind, if there is enough energy, can pick the sand up and
the dunes start to mobilize," he said.
The effect is likely to be most dramatic in the eastern and northern fields.
"These are areas where dunes are currently wooded in many places, so we'll
potentially see major environmental changes that will see currently vegetated
but sandy landscapes revert to active blowing sand seas," Thomas said.
This study, like others before it, highlights the potential for dramatic change
in the African landscape, said Martin Todd of the Department of Geography
University College London.
But while there is broad agreement that temperatures will rise in Africa, he
cautioned there remains significant uncertainty about the outcome on particular
processes such as vegetation cover and dune movements.
"There is a lot of uncertainty about how well our models can simulate
things like precipitation and wind speed, on which this particular model
depends," Todd said by telephone.
Thomas and Wiggs are geomorphologists based at the Oxford University Center for
the Environment. Knight is a dune activity modeler at the University of
Salford's Department of Earth and Life Sciences in Manchester.
Source: Associated Press