The Sahara is the largest of the deserts on the planet and expands from the west to east coast of northern Africa. Inhabitants have evolved to survive the harsh climate of the desert, however they now have to cope with the sprawl of the Sahara into the Sahel – Desertification. There are contrasting opinions on the overall cause of the land degradation; some believe it is due mostly to the influence of humans and others consider changes in the climate to be primarily responsible for the spread of the desert.
There are four main human interactions that are said to lead to desertification: overcultivation, overgrazing, deforestation and poor irrigation. These are influenced by population change and changes in social and economic conditions. Alan Grainger, author of ‘Desertification: How people make deserts, how people can stop, and why they don’t ‘, is a strong believer in the irresponsibility of mans actions in the spread of the desert. He states… “Drought triggers off a crisis, but does not itself cause desertification” In northern Africa, there is a high population growth (Mali NI=3%).
With an escalating population there will be more need to intensify demand on farmland for various crops to be cultivated such as rice and cassava. This leads to several problems that put increased strain on the land. Some of these difficulties include a decline in the fertility of the soil, therefore each time crops are grown they become less successful until they will no longer grow and the land becomes useless, a desert. Also, the topsoil will become crusty by the evaporation of the little rain, which will then increase surface run-off for when it does rain, eroding the soil by gullying.
In the 1960s a large-scale development of groundnuts in the Sahel is said to be significantly responsible for the drought of the early 1970s, as thought by Richard Franke and Barbara Chasin (Montclair State College, New Jersey, USA). Constant harvesting of the large areas of groundnuts due to encouragement from developed countries, like France – with whom they could exchange this product for staple foodstuffs – greatly reduced the amount of fallow land. This meant that nomads who had previously used the land for grazing had to move north where the grazing is then intensified, further increasing the rate of desertification.
This political tie exacerbated a fragile situation. Farmers in the Sahel also cause problems when they graze livestock, mainly goats and cattle. Short-term sedentarisation produces overgrazing, especially when concentrated along walkways and water holes. The walkways are required to transport cattle from each settlement since new “grassy” land has to be found for the livestock when the essential resources end. This nomadic way of life increases the rate of land degradation by placing pressure on the land and the water resources.
Overgrazing leads to a number of problems such as a decline in palatable grass species, especially perennials, which are good at holding the soil together and prevents erosion by rain or wind. “Overgrazing is indeed a major cause of desertification” Irrigation schemes were set up to help stem the problem of desertification. However, these were not managed properly causing further problems. A chain reaction occurs if there is bad irrigation that is summarised in figure 2. Saline soils have good structure and are fairly easily leached but can be reclaimed. Alkaline soils are very compacted and are not good at leaching.
This means that the surface becomes difficult for roots of shrubs and trees to penetrate and the land is hard to reclaim. Deforestation is another one of humans’ influences on environmental change. In the Sahel four million hectares of trees are harvested every year. With deforestation, water evaporates from the soil, is drawn up by capillary rise, leading to a fall in the water table, leaving the topsoil dry and susceptible to wind-erosion. Richard St Barbe Barker, founder of ‘The Men of The Trees Organisation’ shows concern over the effect of deforestation on desertification and says that “When trees go, deserts come”.
Figure 2. Many authors consider land degradation to be caused by global warming and regional climate change. Tereba Togola, a Malian resident is one of these authors and asserts that climate change has taken place for thousands of years and the recent drought in the Sahel is just another one of the many cycles. Togola describes the climate patterns of 4500 years ago, when there were growing oscillations of aridity where dry periods were becoming more frequent. This brought on a period of desertification throughout the Saharan and Sahelian area.
Many of the lakes in the region – Lake Bosumtwi – became dry as a result of the higher temperatures and diminishing amount of rainfall. Large southward population movements to the wetter granite massifs of the Adrar Des Iforas occurred due to the worsening weather conditions. With them, they brought the desert conditions. The sever weather conditions forced them to overgraze and overcultivate the land until it turned to desert where subsequently they had had to move even further south, continuing to erode the land. Authors McIntosh and Tainter illustrate that droughts can be connected with various natural phenomena.
An increase in sea level pressure around the Azores and northern Sahara consequently creates increased anticyclonic activity and augmented winter northeasterly trades, pushing the ITCZ south. If the ITCZ moves south to the warmer southern hemisphere, the subtropical high-pressure area of the Hadley cell dominates the Sahel for much of the year, leading to drier weather and consequently the land degrades. The climate in the Sahel fluctuates greatly from generation to generation causing implications for the people dwelling there.
McIntosh and Tainter say the precipitation variance prevents cultivators from having a regular growing pattern and having to move around to find suitable land. Another natural method of desertification is Sahelian fires that smoulder each year around March and April. These use the parched grasslands as a means of transportation to the surrounding area, destroying all vegetation in its path. The fires can actually be used to control the land by clearing it to produce improved land for grazing potential. Scientists at NASA say… “Benefits… outweighed by the negative impacts f fires on soil fertility, leading to long-term declines in productivity. ” It could be said that researchers have failed to determine the definite cause of the degradation. However, both causes – physical and human – can lead to desertification. It seems possible that Alan Grainger’s theory is most convincing and is worth taking into account; climate change does not actually cause desertification but accelerates the degradation process by human reaction to it. Changes in climate have occurred for millennia leading to increased aridity and the evaporation of lakes in the desert area.
The Spearman’s Rank Correlation Coefficient on the appendix sheet shows if there is a relationship between area of the desert and agricultural population, and area of the desert and rainfall anomaly. Table 1 shows that there is not a statistical relationship and human population has no effect on the size of the desert. Table 2 shows a statistical relationship between the amount of rainfall. Although the spearman rank (appendix 1) illustrates that there is a connection, it is doubtful that rainfall deficiency is the individual cause.
The climate has a strong influence on human actions and in this case humans have had to react to the climate change to sustain a good standard of living, which subsequently leads desertification. Therefore, climate manipulates the way of life of the people but it is the inhabitants themselves that cause the degradation by their exploitation of the land due to their intense farming methods and constant rhythmical travels in the Sahara. If humans were not to use the land so intensively it may have a chance to replenish before the severe drought approaches.