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United Nations is poised to draw up a convention to halt desertification,
the process by which fertile land turns into desert. But are the world’s
deserts really spreading – and if so, why? The short answer is that nobody
knows, and that spells trouble for the convention. One reason for our ongoing
ignorance, say many scientists, is the poor quality of research in the 15
years since the UN Environment Programme (UNEP) claimed a global mandate
to address desertification.

Almost since the beginning of the century, both French and British colonial
scientists have spoken about the ‘advancing sands’ of the Sahara. They variously
blamed diminishing rains and the activities of shifting cultivators and
nomadic cattle herders. In 1949 the French geographer Andre Aubreville coined
the term ‘desertification’ to describe how ‘deserts are being born today
under our very eyes’.

The first quantified assessment appears to have come from the US government’s
Agency for International Development. In 1972, the USAID claimed, without
citing specific evidence, that ‘there has been a net advance in some places
along a 2000-mile southern front of as much as 30 miles a year’.

The idea of an advancing desert front caught on, particularly after
drought and famine devastated the Sahel – the desert margins south of the
Sahara – in the early 1970s. It crystallised at the UN Conference on Desertification,
held in Nairobi in 1977. The conference launched UNEP’s Plan of Action to
Combat Desertification, a global initiative that promoted preventive measures
such as planting trees on sand dunes.

The initiative was a failure. Spending on anti-desertification projects
since has been around $6 billion, but with little tangible effect. Earlier
this year, UNEP’s secretary-general Mostafa Tolba described the initiative’s
outcome as ‘pathetic’. He blamed shortage of money, and proposed spending
a staggering $450 billion over the coming 20 years, probably under the
auspices of the Desertification Convention (proposed at last June’s Earth
Summit), which UNEP is likely to manage.

UNEP defines desertification as ‘land degradation in arid, semiarid
and dry subhumid areas resulting mainly from human impact’. It says that
‘though desertification may be accelerated by drought, it is rarely caused
by it’ and that, because human action is largely to blame, ‘it follows that
it can also be arrested by human action’. But all these statements are
widely criticised. Many researchers argue that most of the apparent growth
of desert regions is caused by changes in rainfall. It follows, they say,
that the potential to halt these changes is much more limited than UNEP
assumes.

Andrew Warren, a geographer from University College London who worked
on a review* of desert and drought policy for the UN last year, says there
are three reasons why land may begin to resemble desert. (His use of ‘resemble’
is deliberately vague: in the past people have assumed too readily that
if land begins to look like desert, it has become permanent desert.) These
causes are: short-term drought, longer-term climate change, and the destruction
of soils and vegetation through human activity. ‘You need a different response
for each one. The problem is how to distinguish between them,’ he says.

It is a problem that neither UNEP nor the scientific community has successfully
addressed in the 15 years since the launch of the Plan of Action. The question
today for policy makers is whether there is any point in throwing money
at proposed solutions when the problem is so badly understood. Without better
science, many desert researchers say that a desertification convention will
prove as ineffective as previous efforts.

DESERTS WON’T WAIT

The counter-argument is that the desertification crisis is too grave
to wait for science. UNEP has frequently claimed that ‘each year 21 million
hectares of once-productive soil are reduced by desertification to a level
of zero productivity, and 6 million hectares become total wasteland beyond
economic recoverability’. This is a lot of land: 21 million hectares is
almost the size of the British Isles.

But where did these figures come from? The answer is a 1984 report by
UNEP, based largely on replies to a questionnaire sent to governments in
1982. Those replies ‘have an extraordinarily shaky basis,’ wrote Ridley
Nelson, a senior researcher at the World Bank, in a 1988 bank working paper.
‘The use of this data seems to have been very casual . . . particularly
since in Africa they were completing it in many cases at the height of
a drought’.

Did the data show the effects of short-term drought or long-term change?
Nobody knows. The same failing under-mines another critical study that put
statistical flesh on the hypothesis of advancing deserts. In 1975, Hugh
Lamprey, a bush pilot turned environmentalist, concluded from a study of
northern Sudan that ‘the desert southern boundary has shifted south by an
average of 90 to 100 kilometres in the last 17 years in several areas.’

Nelson found that Lamprey’s study, which has been widely disseminated
by both UNEP and the government of Sudan, had become the ‘main source’ for
the idea of an advancing desert front. It underpinned the Plan of Action
in 1977, for example. And in 1986 it led George Bush, then vice-president,
to consider more US aid for Sudan because ‘desertification was advancing
at 9 kilometres per annum’.

But was this image of shifting sands correct? Lamprey had reached his
conclusion by comparing his own observations of vegetation, taken from a
light plane during one month at the height of the drought of the early 1970s,
with rainfall statistics from 1958, the end of a wet phase in the region.
It is far from clear, say critics, how he made this comparison. Certainly,
said Warren in a report written in 1988 with his colleague Clive Agnew,
Lamprey ‘failed to distinguish between the effects of the drought and of
»å±ð²õ±ð°ù³Ù¾±´Ú¾±³¦²¹³Ù¾±´Ç²Ô’.

MISSING EVIDENCE

Ulf Hellden and other researchers at Lund University in Sweden spent
most of the 1980s examining satellite images and historical records to find
signs of the Sahara’s advance in Sudan. Lamprey had singled out the area
around the village of Kheiran in northern Kordofan as exhibiting desert
advance. But Hellden found that the presence of local sand dunes was ‘reported
as early as 1911 . . . The system is not rolling southward and it is not
connected with the Sahara desert.’

His team concluded at the end of last year that ‘none of these studies
verified the creation of long-lasting desert-like conditions in the Sudan
during the 1962-1984 period which corresponded to the magnitude described
by many authors’. Driving home the message, they said: ‘There was no trend
in the creation or possible growth of desert patches . . . no major shifts
in the northern cultivation limit . . . no major sand dune transformations
. . . and no major changes in vegetation cover and crop productivity .
. . which could not be explained by varying rainfall characteristics.’

And what applied to Sudan appeared to apply along most of the southern
edge of the Sahara. Studies of satellite images by Compton Tucker of NASA’s
Goddard Space Flight Center in Maryland have showed that the desert boundary
oscillates by tens of kilometres from year to year, depending on local rainfall.
Commenting on those findings, Sharon Nicholson, a leading desert meteorologist
from Florida State University in Tallahassee, said: ‘The message is that
a lot of what’s being claimed about the so-called desertification of the
Sahel is just incorrect.’

Desertification, says Warren, has generally been ‘perceived as a long-term
process of degradation which accelerated during periods of intense drought’.
UNEP has frequently called it ‘irreversible’. But the desert margins seem
to be much less fragile than is usually assumed, and far more dynamic. According
to Nelson, ‘Recovery of apparently irreversible degraded areas following
better rainfall can be astonishing, even to experienced observers.’ For
example, after successive droughts in Ethiopia in the 1980s, vegetation
burst forth within hours of the first rains returning.

Michael Mortimore, a geographer who has researched the desert in northern
Nigeria for 20 years, concludes that ‘arid and semiarid ecosystems are adapted
to frequent climatic oscillations’. One measure of this resilience is the
agricultural production of the Sahel. When an international panel called
together by the Swedish Agency for Research Cooperation with Developing
Countries assessed the evidence for spreading deserts in 1990, it reported
that crop productivity in the Sahel over the past 25 years showed no downward
trend that would indicate severe desertification; instead, it varied with
rainfall. The available data ‘do not support the common belief that agricultural
systems in the Sahel are near collapse’.

In the face of this sustained assault on conventional wisdom, UNEP has
been shifting its ground. It has finally dropped the shifting sands hypothesis,
even in publicity material. Instead, it proposes a revised model, encapsulated
in a public relations feature distributed to the media by its public affairs
departments earlier this year: ‘Whether the deserts of the world are receding
or advancing is not the issue . . . the process of desertification is not
shifting sand dunes, or the advance of a wall of sand, but rather patches
of increasingly unproductive land ‘breaking out’ and spreading over hundreds
of square kilometres.’ The centres of such patches were villages and water
holes, where people and animals were destroying vegetation and soils.

But this model is also under attack. Hellden concluded last year from
his satellite pictures of Sudan that ‘there was no trend in the creation
or possible growth of desert patches around 103 examined villages and water
³ó´Ç±ô±ð²õ’.

Warren told the UN last year that ‘even the view that cattle watering
points act as centres or poles of desertification is now questioned’. In
central Sudan, he found evidence of this at only 7 out of 77 watering holes,
‘even in drought years’. Likewise, when researchers in Senegal used satellite
pictures to look at 20 deep wells on the desert margins, they found, according
to Hellden, ‘no consistent relationship between primary productivity and
proximity to a well’.

Warren suggests that although the cattle may trample and damage a small
circle around the watering point itself, they may also fertilise the pastures
in a circular zone beyond. Thus they could actually increase the amount
of vegetation.

Such findings help undermine what was for many years one of the central
assumptions of the desertification debate – that the cattle herders of the
Sahel are creating deserts by allowing their animals to overgraze pastures,
especially around watering holes. Warren, in his UN report, said that ‘only
under very extreme densities of cattle’ is soil erosion serious: ‘overgrazing
has been greatly overestimated as an environmental problem.’

The argument was already looking a bit thin, according to Nelson. ‘The
two conventional wisdoms – that on the one hand livestock numbers have been
rising for a long time, well beyond the calculated sustainable carrying
capacity, and that on the other hand the productivity of rangelands has
been falling for a long time – do not lie at all well together.’

In fact, traditional nomadic herders often seem to know far more about
the innate resilience of the vegetation of the Sahel than botanists trained
in the West. Their herding methods, based on constant migration and fluctuating
herd sizes, work better in the unpredictable environment of the desert margins
than does settled ranching.

Agnew points out that in Mali, the nomadic Fulbe herders on the desert
margins have better pastures than those found in the wetter savanna lands
to the south, presumably because their land is better managed. This observation
also raises an interesting question about how deserts are defined; indeed,
it throws every argument, on both sides of the desertification debate, into
confusion. The amount of vegetation, it seems, is a very poor measure of
the desert margin.

Take a flight across the semidesert border between Israel and Egypt,
and you will see that the Israeli Negev is greener than the yellowish Egyptian
Sinai. The reason is that Sinai pastures are grazed lower than those in
the Negev. They contain less biomass. Any analysis of satellite pictures,
which essentially measure biomass, would describe the Sinai as more ‘desertified’
than the Negev.

But are such assumptions fair? According to Agnew and Warren, ‘there
are good scientific arguments for the case that pastures are more productive
when they are grazed low – in other words, when they appear more desert-like.
Up to a point, plants produce more new and fresh growth if they are encouraged
by being grazed, and they may be less vulnerable to drought if they are
kept small’.

FALSE PICTURE

For analysts of satellite pictures, such pitfalls are troubling. In
parts of East Africa declining rainfall and (it is claimed) overgrazing
have destroyed grasses, causing thorn scrub to take over. Few would deny
that this is a downward ecological step, though it may be easily reversed.
Yet, as Warren and Agnew point out, ‘The invasion of thorn scrub increases
biomass and would appear on satellite imagery as an increase in vegetative
³¦´Ç±¹±ð°ù.’ In other words, it would look as if the desert was retreating when
it was actually advancing.

The growing importance of satellites in assessing the state of the land
may encourage scientists to use indices of vegetation to assess whether
deserts are spreading. But researchers such as Warren believe that the state
of soils, which can not be seen so easily from space, is more important.
Changes to vegetation, such as withering, can easily be reversed by a drop
of rain. Those to soil, such as loss of nutrients, may not.

So far, the scientific community has failed to answer the key questions
about the extent of man-made desertification. The 1990 expert panel in
Sweden concluded that ‘there has not yet been any international effort to
actually monitor and document the desertification through repeated observations
in the Sahel’.

Many blame UNEP, an agency with a remit from the UN to further the environmental
sciences, for offering spurious certainty in place of a proper research
programme. ‘UNEP sometimes likes to point to its scientific status,’ says
Hellden, ‘but they have never raised the money to assess the real status
of desertification.’ Pressed on this point, a spokesperson for UNEP told
New Scientist: ‘It is not UNEP’s fault, but rather a regrettable global
state of affairs that nobody still has a world map of vegetation or soil
³¦´Ç±¹±ð°ù.’

STATE OF FLUX

The research that has been done suggests that the old presumptions are
mostly wrong. Nomadic herdsmen do not, by and large, destroy their pastures.
On the contrary, they use it best. If there is overfarming, it has yet to
cause widespread reductions in crop yields. There is no natural ecological
equilibrium in the Sahel, only constant flux.

Even the case against the evils of population growth on desert margins
is unproven. Researchers ‘have not found it easy to relate population densities
to degradation’, says Warren. Mortimore points out in his book, Adapting
to Drought (Cambridge University Press, 1989), that in the arid but densely
populated farming region around Kano in northern Nigeria, greater numbers
of people can benefit the land, because the larger workforce can carry out
all manner of labour-intensive soil and water conservation and tree-planting
schemes. ‘There is an inherent contradiction in calling simultaneously for
intensified conservationary land use and for family planning,’ he says.

Some researchers refuse to accept the new mood of uncertainty. In a
1991 paper for UNESCO, the French government researcher Henri Le Houerou
claims that ‘the mechanisms (of desertification) are perfectly described
and well known’, adding that ‘overgrazing is predominant in the Sahel’.
And, though UNEP is more cautious in its scientific reports, it often joins
in in its publicity material. A ‘fact sheet’ published this summer declares
in its concluding paragraph: ‘Clearly the causes of land degradation are
well understood.’ Well, clearly not.

Despite having a mission as a scientific agency within the UN, UNEP
has frequently used statistics in a cavalier manner. For many years, it
claimed that 35 per cent of the world’s land area is ‘threatened’ by desertification.
This, says Warren, turned out to be a measure of all the arid zones on the
planet, half of which are too arid for any form of agriculture. In what
sense, then, is it threatened? This year, UNEP has a new figure: 25 per
cent of the planet is ‘involved’ in desertification.

UNEP says that ‘approximately 25 400 million tonnes of material is removed
each year from topsoils . . . much of it in drylands.’ But the main source
for this remarkably precise statistic, the 15-year Global Assessment of
Soil Degradation, funded by UNEP, emphasises that the findings are an order-of-magnitude
best guess. The real figure could be ten times greater or ten times less.

Mortimore says that UNEP’s ‘continued reliance’ on such poor data ‘demonstrates
the failure of UNEP to fulfil its monitoring responsibility’. The 1990 Swedish
panel complained that ‘the effects of desertification in Africa and elsewhere
are not documented according to scientific standards. The need for basic
research is as obvious today as it was in 1977.’ UNEP can reasonably claim
that national governments deny it the money to conduct proper research.
But one former UNEP researcher who spoke to New Scientist says that what
is done is often of poor quality and the interpretations often bizarre.

‘We don’t understand where UNEP gets most of its figures,’ says Hellden.
‘Some of them are just fantastic. They should realise that they can’t go
on like this.’

The neglect of research dooms aid projects to failure. As the Swedish
panel concluded: ‘Anti-desertification measures and land rehabilitation
development projects can only be successful if based on correct diagnosis.
Our present knowledge is inadequate to formulate policies for socioeconomic
change in Africa in the name of desertification.’

Conspicuously, UNEP’s desertification initiatives remain based on the
premise that most land degradation in arid zones is a consequence of human
activity – and thus can be rolled back by further human interventions. ‘UNEP
has to believe in man-made desertification because that justifies the intervention,’
says Hellden. But the premise does not stand up to scientific scrutiny.
It may even be largely false. ‘You cannot take big decisions about the future
of arid Africa without the data on what is really happening to the environment
of 200 million people,’ concludes Hellden. ‘But UNEP has failed to do that.’

The tragedy is that phrase ‘»å±ð²õ±ð°ù³Ù¾±´Ú¾±³¦²¹³Ù¾±´Ç²Ô’. Adopted as a catchphrase
to encapsulate a series of poorly-understood problems in arid lands, it
has turned into a burden that prevents understanding. As one scientist who
left the UNEP desert programme in disgust at its poor research standards
put it recently: ‘I wish the term desertification had never been invented.’

* Assessment of Desertification and Drought in the Sudano-Sahelian Region
1985-1991