The myth of the marching desert

The world's deserts are on the move, engulfing entire nations in their path. That is the myth. But is it true? What is "desertification"? And has the UN wasted billions of dollars because it failed to answer this basic question?

Bill Forse

NEW DESERTS are forming from Mexico to Rajhastan and from Mauritania to Botswana. The process is called desertification. The world has an image to go with the word: an emotive picture of inexorably shifting sands encroaching on valuable farmland.

The word and the image have sustained a decade-long effort by the United Nations Environment Programme (UNEP) to combat the spread of deserts. Now an increasing number of scientists are arguing that the image is a mirage and the efforts have been largely misdirected. Countries such as Mali, on the southern fringes of the Sahara desert, have used international aid to plant millions of trees as a barrier against the encroaching sands. But is the desert really moving?

Soils around the world are suffering from various forms of degradation -- that much is certain. The damage is worst in the dry lands, which cover roughly a third of the land surface of the planet and support some 850 million people. But the fear is that attempts to encapsulate this problem with the phrase "desertification" have obscured possible solutions.

The UNEP claims that desertification costs $26 billion a year in lost food production. The damage, it says, could be prevented by spending $4.5 billion each year. But to date, the programme's calls for funds have fallen on deaf ears. A meeting of Descon (the UN body responsible for combating desertification) in Geneva last November heard that less than 10 per cent of this money had been raised.

But the real argument is about whether what money has been spent has been spent wisely. There has been "too much unfounded assertion and exaggeration", says Ridley Nelson in a paper published recently by the environmental arm of the World Bank. And Jeremy Swift, in a paper from the Institute of Development Studies claims that existing definitions of the problem of desertification have led to "big public policies being based on very little bits of science".

The notion of the advancing deserts is old. Shifting sand dunes have engulfed desert settlements throughout history. Here and there, they still do. But should we conclude that expanding deserts are the principal threat to arid lands? The new critics of UNEP say that we should not.

The UN's prime initiative on deserts, which set the current tramlines for halting the degradation of soils in dry lands, was the Conference on Desertification (UNCOD) held in Nairobi, Kenya, in 1977. The conference produced a world map of desertification and asserted, among other things, that the Sahara desert of North Africa had moved south by about 100 kilometres between 1958 and 1975, an average of 6 kilometres a year.

A major review of the action against deserts was held by the UN in 1984. Mostafa Tolba, the director of the UNEP said then: "Currently, 35 percent of the world's land surface is at risk . . . each year, 21 million hectares is reduced to near or complete uselessness."

These figures have become part of the furniture in the study of desertification, enshrined, as Nelson put it, as "institutional fact". The numbers frequently accompany compelling pictures of forlorn children standing on their dune-covered homes, and turn up in books and papers from the UN with titles such as "Rolling back the desert" and "Deserts on the march". All this has focused attention on the edges of existing deserts. This, say the critics, is a major error.

"There is extremely little scientific evidence based on field research or remote sensing for the many statements about the extent of desertification," says Nelson. Many of the figures come from the answers to a questionnaire sent out by the UNEP in 1982. The answers to that questionnaire probably mean very little, says Swift "In Africa, governments were completing it in many cases at the height of a drought," says Nelson. Experts even from sophisticated governments say they had great difficulty answering the questions. They had little of the data that they were asked for. There were no proper guidelines for how to answer critical questions about the degree of desertification of land.

The UN's figure for the southward march of the Sahara comes from an investigation conducted in 1975 by Hugh Lamprey, an ecologist who is now director of the Worldwide Fund for Nature in East Africa. He said: "The desert's boundary had shifted south by 90 to 100 kilometres between 1958 and 1975."

In a paper published last November, two geographers from University College, London, Clive Agnew and Andrew Warren, dispute this claim. The estimate of the position of the edge of the desert in 1958 they say, was based on very limited data from weather stations. Moreover, in 1975, there was a drought. Lamprey failed to distinguish between the temporary effects of the drought on the boundaries of the desert and any permanent "desertification", they say.

Warren and Agnew also query Tolba's claim that 35 percent of the world's land is "at risk". "This is the area that is arid and at least half of that area is very arid -- too arid for any form of agriculture." It is hardly "at risk", they say.

The term "desertification" is deeply flawed, says Camilla Toulmin of the International Institute for Environment and Development (IIED), a UN-funded agency based in London. There is little agreement among scientists about what it means. Some use the term to imply an irreversible change. Others do not. Some want to include changes due solely to a decline in rainfall. Others say this should be excluded.

The UN defines the process as "the diminution or destruction of the biological potential of land that can lead ultimately to desert-like conditions". This definition is so wide that it includes, for instance, waterlogging from irrigation canals. Nelson says that the process must be caused "at least partly by man". He says that the process is not one of expanding deserts but rather is a complex process of "pulsing deteriorations" emanating not from desert margins, but "radiating out from centres of excessive population pressure". This is a sharply different view suggesting an entirely different agenda for governments and aid agencies. Nelson's view is that the main pressure for desertification is not the spread of sand dunes, but the spread of people.

There are, of course, places where the desert can be seen encroaching on neighbouring land, and where it can be held back, more or less literally. Stephen Bristow of SOS Sahel, a British charity, has done work at Shendi on the banks of the Nile in Sudan where, as trees are eaten by livestock, the sands take over. SOS Sahel is successfully fighting the desert by planting new trees, he says.

The debate about what turns useful land into desert centres on whether it is the fault of humans or the inevitable result of changes in climate. The suggested human culprits include short-sighted governments and farmers, poverty and growth in population. The people who suffer tend to blame natural events.

Some researchers stress the decline in rainfall across the Sahel since the late 1960s as being at the heart of that region's recurrent crisis. But it is not clear how permanent such changes may prove.

Swedish researchers say that even after years of drought in the Sahel, there are few real signs of irreversible land degradation in the area of the Sudan that they have studied in detail. "The creation of desert-like conditions seemed to occur mainly in drought periods." When the rainfall returned to normal, as it did this summer in much of the region, "the productivity recovered".

One study concludes: "No ecological zones have shifted southwards and the boundaries between different vegetation associations appear to be the same now as they were 80 years ago."

Satellite studies of the Sahara in the 1980s do not show an inexorably advancing desert but rather "a generally southward retreating vegetation front in the Sahel in 1982 to 1984 and a generally northward advancing vegetation front in 1985, 1986 and 1987," says Nelson.

Parts of the Sahara turn green rapidly whenever rainfall returns. Researchers in the arid lands of Australia also point to a recent remarkable recovery of some badly degraded soils in New South Wales and claim that improved rainfall is a prime reason for this.

The only sensible strategy for many places hit by "desertification" could thus be to wait for the rains to return. But that, says Swift, depends on some knowledge of whether a drop in rainfall is part of a short- or long-term trend. If, as some suggest, the Sahel is drying out because of some consequence of the greenhouse effect, the African farmers could be in for a long wait.

The truth is that there is not enough long-term data to predict trends, says Graham Farmer, a climatologist at the University of East Anglia. He points out that computer models are not yet good enough to tell whether global warming from the greenhouse effect will make the Sahel wetter or drier.

Even short-term predictions are shaky. Last spring, the Meteorological Office in Britain predicted one of the driest summers for the Sahel "in a hundred years". In June, on the basis of changes in the ocean currents and temperatures in the Pacific and Atlantic oceans, the office revised its prediction to a very wet season. The second forecast was correct, as the region experienced the wettest rainy season for at least 20 years.

An assessment of exactly how much land turns into desert each year hinges largely on definitions. Most researchers are skeptical about the figure of 21 million hectares of land lost each year, which is repeatedly quoted by the UN.

Satellite images are an obvious source of data. But there are problems. One report by the UNEP of desertification in Bangladesh mistakenly included all the paddy fields as desert because they were dry at the time when the pictures were taken. And the spread of thorn bushes in East Africa is destroying feeding grounds for nomadic cattle herds. Yet a satellite will register increased biological productivity.

Critics of the orthodox idea of spreading deserts say it is still implanted in the minds of policy-makers. The Brundtland Report, currently the most-quoted document on the environment and development, contains a chapter on the "advancing desert" that simply quotes all the UN's statistics.

The president of the World Bank, Barber Conable, in a speech marking the conversion of his organisation to a Breener perspective, said: "We know we must stop the advance of the desert . . . in Mali, the Sahara has been drawn 350 kilometres south by desertification over the past 20 years."

With the wrong problem planted in the minds of decision-makers, some of the policies adopted to fight the loss of land have been "futile and even damaging", say the critics. This can affect the lives of millions of people since land degradation is a major ingredient in the recipe for famine.

Correct diagnosis is essential in responding to crises in the dry lands of the world. As Warren and Agnew put it: "If the problem is thought to be drought, lasting no more than two or three years, food aid may be adequate. If it is seen as climatic change, permanent withdrawal is called for. If there has been near-complete devegetation, in the absence of a climatic change, the treatment is reseeding or replanting. If the diagnosis is that the desert is actively expanding at its margins, then same kind of holding line might be the answer."

Warren says: "If you trade on false statistics, you get ridiculous schemes like the trans-Saharan green belt." There is no point in planting trees to halt the desert's progress if it is not moving or if the changing climate won't let the trees grow.

Many countries, including Mali, Algeria, Iran, Sudan and Somalia, have planted trees in an effort to halt the desert. Yet, say Warren and Agnew, "active sand dunes seldom threaten valuable land . . . the cost-benefit of planting is low or negative. But planting is visible and gives the impression that something is being done."

Swift wants more basic research into land degradation, and believes that people with entrenched views on the subject have prevented the release of money for this in the past. Some new projects have started. Last year, the International Livestock Centre for Africa, in Addis Ababa, Ethiopia, began a five-year project to monitor vegetation, livestock and rainfall and the effects of drought. The International Union for the Conservation of Nature (IUCN), which is run by a former chief scientist at Britain's Department of the Environment is looking at new ways of managing natural resources in the Sahel. In November, the IUCN published its first Sahel Environmental Status Report, which aimed to relate crop yields and rainfall across the Sahel.

Some governments and aid agencies are already changing their views. Consultants from Mali and China, working with the UN Sahelian Office, have taken a second look at the 1985 Malian national plan to combat desertification. That plan proposed building a "green belt" of trees across Mali to halt advancing sand dunes. The consultants say that this was founded on the erroneous idea that it was possible to block the southward march of the Sahara. The new idea is to intervene in the life of individual villages to halt soil degradation.

The redefinition of the problem does not make solutions any easier. Says Nelson: "Soil degradation is a problem that won't readily be solved by an annual investment. Both it and the solution are less certain and in many respects more difficult."

"Basic research," say Warren and Agnew, "must precede the monitoring that is such a popular cause among the desertification organisations. We cannot know what to monitor if we do not understand the basic processes, and their impact on people's lives.