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Drought, desertification, and water management in Sub-Saharan Africa
Droughts in Sub-Saharan Africa and their implications for planning and development
Land degradation and management of soil and water
Edouard G. Bonkoungou
For Sub-Saharan Africa as a whole, consisting of 45 countries, gross national product per person in constant dollars fell by 20 per cent between 1977 and 1986. May (1988) reports that the average person in many of these countries is now poorer than at the time of independence about 30 years ago. Whereas Latin America and Asia have become almost self-sufficient in cereals, Africa has grown more dependent on imports and food aid. Total food production has, in fact, increased but not enough to keep pace with population growth. During the past 30 years agricultural production in Sub-Saharan Africa has risen by 2 per cent a year, while population is growing at the rate of about 3.2 per cent a year, faster than any other region has ever experienced (World Bank 1989).
The constraints on development in Sub-Saharan Africa are many and varied, including the following: a difficult climate with frequent episodes of severe drought in the semi-arid lands; fragile soils prone to erosion and nutrient depletion; a very fast rate of population growth; a heavy external debt burden. The world economy has not favoured Africa. Declines in Africa's commodity export prices and increases in the import prices of manufactured goods and oil have deteriorated the terms of trade and worsened Africa's external debt burden. Although this is true of all third world economies, the impasse in Sub-Saharan Africa is most striking.
Yet, as Harrison (1987) points out, the economic crisis is dwarfed by the continent's deepening environmental crisis. In the semi-arid regions, for example, recurrent droughts and population pressure have led to destruction of vegetation resulting in desertification, erosion, and depletion of soil fertility. Although the outlook is rather gloomy, there are individual projects that have succeeded against a background of general failure. If we could read the lessons of their successes, we might be able to piece together the formula, as Harrison (1987) puts it, and find some way of breaking through the development impasse.
This paper highlights some of the major environmental constraints in Sub-Saharan Africa and points to their implications for sustainable development strategies in the region, with a focus on semi-arid lands.
Droughts in Sub-Saharan Africa and their implications for planning and development
Recurrent droughts are a salient feature of the semi-arid lands of Sub-Saharan Africa, especially the Sahel. Rainfall fluctuates widely in time and space in a way that has not yet been understood and therefore cannot be easily forecast. The implication of this extreme variability for planning and development is that the concept of "mean" or "average" rainfall has little value.
Some of the main characteristics of the drought-prone climate of the region are presented below.
Rainfall fluctuation in time
The recent drought in the Sahel is not unique in the history of the region. Droughts of this magnitude and extent have occurred in the past. Nicholson (1982), using records of harvest quality, lake levels and river flow, rainfall data, and climatic description, reconstructed past episodes of droughts and good rainfall (see figs. 8.1 and 8.2).
For example, a wet episode lasted from about 1870 to 1895. Harvests were consistently good in the semi-arid regions of Namibia, southern Angola, and South Africa. North of the equator, the Niger Bend region near Timbuktoo, Mali, in the Sahel yielded abundant crops and the region became the "bread basket" of West Africa. Today, annual rainfall in the area is only about 200 mm, below the rain-fed agriculture boundary.
Fig. 8.1 Trends of African indicators of lake and river levels, rainfall, and harvest quality, 18801920 (Source: Nicholson 1982)
Fig. 8.2 Annual rainfall fluctuations in the Sahel, 1900-1982 (Source: Sircoulon 1992)
About 1895, a major change towards more arid conditions occurred and the "desiccation" culminated in severe drought around 19131914.
In more recent decades, rainfall was more abundant in the 1950s, with records as high as 30 to 60 per cent above "normal." But this episode ended abruptly towards the end of the 1960s, giving way to the extreme drought of the early 1970s when rainfall went down 15 to 35 per cent below normal in the Sahel. In some areas, rainfall during the 1968-1973 period was 50 per cent lower than during the 1950s.
Fluctuations are often abrupt and extreme, with droughts recurring at irregular intervals. The change from wetter conditions to persistent drought cannot as yet be forecast. Thus the implication for planning and development is that the carrying capacity of the land should be that of the driest years, not the "average" year.
Clustering and persistence of abnormal years
An unusual feature of rainfall fluctuations in the region is their extreme persistence for one to two decades or more.
In most humid areas, dry and wet years are generally randomly interspersed. In some arid regions, however, abnormal years tend to cluster together. In the Sahel, this characteristic is extreme: wet or dry conditions may persist for one or two decades. As an example, the period 1960-1980 was rather consistently dry. Droughts lasting one or two decades are also evident in the historical records mentioned earlier.
A study by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT 1988) illustrates this feature. Change in rainfall variability in semi-arid lands in India and the Sahel was compared by analysing long-term climatic records for Niamey in Niger and Hyderabad in India. The variability in annual rainfall at the two locations is shown in figure 8.3. In 87 years (1901-1987) at Hyderabad, the time-series showed no significant trend, and the rainfall in a given year is not correlated with that of the preceding or the following years. At Niamey in the Sahel, variability of annual rainfall from 1905 to 1987 revealed a different pattern. Compared with Hyderabad, Niamey has longer sequences of consecutive "dry" years with below-average rainfall, and much fewer "wet" years. Droughts are longer in the Sahelian zone.
The clustering of abnormal ("wet" or "dry") years seems to be unique to the Sahel. Other semi-arid lands in Africa do not exhibit this characteristic. Comparison of climatic data between the Kalahari region in southern Africa and the Sahel showed that, although drier (and wetter) periods tend to occur synchronously in both areas, the decadal persistence observed in the Sahel is not a distinct feature of rainfall fluctuation in the semi-arid lands of southern Africa; dry episodes coincide in the two regions but the years of most intense drought do not (Nicholson 1982). Although the recurrence of drought has been shown to be cyclic in some semi-arid regions, this has not been clearly established for the West African Sahel.
High spatial variability is a well-known characteristic of Sahelian rainfall (figs. 8.4 and 8.5). The reason for this spotty distribution is the convective nature of the rains, i.e. the showery type, as shown in figure 8.6; the falling of rain from a cloud generally signals the onset of dissipation of the cloud, which may grow again and produce intense rainfall further away.
Fig. 8.3 Variability in annual rainfall in Niamey, Niger, and Hyderabad, India (Source: ICRISAT 1988)
Implications for planning and development
The implication of this extreme spottiness for regional planning is frightening. Two villages only 1 km apart can experience entirely different rainfall regimes at one time or another during the season, even during a year when total rainfall is comparable in both locations. For a given rainstorm, one village may be drenched while its neighbour remains dry. If this happens at a crucial time for crop development - e.g. when seedlings are establishing themselves or grain is maturing - this can mean a good harvest for one village and total crop failure for its neighbour.
Fig. 8.4 Spatial variability of rainfall on 12 and 13 June 1986 in Ouagadougou, Burkina Faso (Source: Rochette 1989)
Other features of the Sahelian climate described earlier pose equally serious constraints for planning. Persistent years of aboveaverage rainfall can create a false sense of the true climatic conditions and mislead farmers and pastoralists to extend their activities into the marginal desert fringe beyond the true agronomic dry boundary. They may then become trapped in this fragile environment during a drier period; the environmental damage that then occurs is intensified. This may have contributed to the disaster accompanying the droughts of the 1970s, which succeeded a very "wet" period in the 1950s.
As Nicholson (1982) summed it up, the characteristics of the Sahelian climate that should be kept in mind include the low and highly variable rainfall, the prevalence of dry years, the extreme magnitude of the variability, the rapidity with which new persistent conditions can be established, and the spottiness of rainfall even in "normal" years. The "persistence" feature of the Sahelian climate is a clear message to planners that technologies and strategies that have produced good results in other semi-arid regions of the world may not be expected necessarily to work in the Sahel.
Fig. 8.5 Spatial variability of rainfall shown as isoheyets measured on a 400 m grid over 500 ha at the research station of the ICRISAT Sahelian Centre, Niger, 22 July 1986 (Source: ICRISAT 1988)
The task ahead is immense. A complete understanding of the climatic peculiarities of the semi-arid lands of Sub-Saharan Africa and the tuning of development planning to these characteristics deserve sustained efforts. On-going programmes/projects and recent initiatives in this direction include those by the Regional AgrometeorologicalHydrological Centre, the Sahelian Centre of ICRISAT, the African Centre of Meteorological Applications for Development, the Sahara and Sahel Observatory, and the International Geosphere-Biosphere Programme in the region. This development is encouraging, but a breakthrough is still awaited.
Fig. 8.6 Continual growth and decay of a typical convective cloud as it moves downstream with the wind (Source: Nicholson 1982)
Pressures from human and livestock populations coupled with the effect of recurrent drought have led to serious degradation of vegetation cover, erosion, and depletion of soil fertility on a large scale in many parts of Sub-Saharan Africa. Desertification, as this tragic land degradation is referred to, threatens the drylands of Sub-Saharan Africa in a larger proportion than any other region in the world. Once the vegetation cover is removed, the fragile soils are exposed to winds and battering rains. Erosion is inevitable. Early storms are often accompanied by strong winds. Wind speeds exceeding 100 km/hour have been recorded at ICRISAT Sahelian Centre in Niger. Blowing sand subjects seedlings to abrasion and often results in their being completely covered by sand, causing serious problems in crop establishment (Kalij and Hoogmoed 1993). In many areas this takes dramatic forms: shifting sand dunes that swamp villages and fields, formation of deep gullies, crusts that seal the soil surface and markedly increase runoff.
Desertification has been described as self-propagating (Harrison 1987): as expanding areas become useless for crops or livestock, the pressure on the islands of remaining fertility increases. Farming is taken beyond the limits of sustainable rain-fed agriculture. Whole families, sometimes whole villages, migrate to better-watered areas. There they begin the process of deforestation, overcultivation, and overgrazing anew.
Implications for development
The traditional solution
Over the centuries African pastoralists and farmers had developed efficient systems of land use compatible with their environment. For example, nomadic pastoralists traditionally moved with herds of animals to different areas of good grazing and water supply. With low stocking levels they were able to move to new areas before the reserves of any single area were depleted and the soil laid bare.
The parkland system of cropping under tree cover, a widely practised farming system in the Sahel, is probably the most elaborate traditional agro-forestry practice known today in any of the semi-arid zones of the world. In most instances, however, farmers have relied on natural processes for the regeneration of the woody component.
The current level of population pressure, however, precludes true nomadic grazing or passive reliance on natural regeneration to maintain adequate tree densities in the farmlands. Many of the traditional solutions are no longer viable. The severity of land degradation alerted the governments and the international community and led to the creation in 1973 of CILSS (Comite Permanent Inter-Etats de Lutte contre la Secheresse dans le Sahel). Major efforts by the international community to combat desertification include the 1977 UN Conference on Desertification in Nairobi, Kenya, the creation of the United Nations Sudano-Sahelian Office, and the agreement at the Rio Summit in 1992 to negotiate a convention on desertification. The agreement commits governments, relevant non-governmental organizations, and the scientific community to prepare and adopt an international convention to combat desertification in all affected areas of the world, particularly in Africa.
Technical interventions introduced so far to combat desertification have met with very limited success. Some of the reasons for this debacle include the misunderstanding of the nature of the problem, which was initially conceived solely as the responsibility of the government departments in charge of forestry; hence, the overemphasis on planting fast-growing species in woodlots and green belts. The failure properly to diagnose people's perception of the problem and to identify the felt needs of local populations fuelled antagonistic relationships between foresters and peasants. This was because modern forestry, contrary to traditional wisdom in the region, has been considered to be separate from agriculture and livestock. Harrison (1987) noted that "foresters viewed farmers and herders as vandals, destroyers of forests to be kept out at all costs. Peasants saw foresters as policemen who excluded them from land that was traditionally theirs to control and use. Under such conditions the forests did not flourish." I have expressed similar views elsewhere (Bonkoungou 1985, 1987, and 1990) and pointed out the risk of some foresters failing to see the people for the forest.
The situation described above explains many of the failures in the fight against desertification. Yet trees and shrubs have a crucial role to play in the future of farming and pastoralism in Africa, as is becoming convincingly clear from research results of the International Centre for Research in Agroforestry (ICRAF).
The potential of agro-forestry to combat desertification and sustain agricultural production
Baumer (1987) extensively discusses the potential of agro-forestry to combat desertification. As mentioned above, research results from ICRAF indicate that agro-forestry has great potential for mitigating tropical deforestation, land depletion, and rural poverty. Trees integrated with crops or livestock meet wider needs than do woodlots. If properly spaced and managed, they serve as windbreaks and shelterbelts. They mark boundaries and strengthen terraces. They supply not only fuel, timber, stakes, and poles but also cash crops, fodder, fruits, nuts, leaves, and pods for human and livestock feed, gums, and medicines. In addition to the above products and many others, trees and shrubs also render various services in environmental protection: shade, improvement of soil fertility, etc.
As Harrison (1987) so ably advocates, agro-forestry offers by far the speediest road to reforesting Africa. Many African farmers already practice one form or another of agro-forestry but have relied mostly on natural regeneration of woody species, which is no longer reliable because of the much-shortened fallow periods. The task ahead then, as Harrison (1987) puts it, is "to convert African farmers and herders from passive to active agroforesters; from users of selfplanted trees, to tree farmers."
ICRAF does just that. Established in 1978, with headquarters in Nairobi, Kenya, ICRAF implements research jointly with national institutions through networks associated with the major eco-regions. One such network, the agro-forestry research network for the SemiArid Lowlands of West Africa was launched in 1989 with the objective of generating appropriate agro-forestry technologies for the ecoregion and strengthening national agro-forestry research capabilities in the subregion.
Land degradation and management of soil and water
From the discussion presented above on drought and desertification, it is apparent that the fragile soils of semi-arias lands of Sub-Saharan Africa are exposed to increasing threats of wind and runoff erosion. It is also evident that water is a scarce, high-value economic resource in the region. In addition to high rates of evaporation, because the rains usually come during the hot period of the year, other major routes of water loss include soil evaporation and runoff owing to poor infiltration in the soil. Rains in the semi-arid lands of Sub-Saharan Africa do not fall gently and evenly; they come predominantly in convective storms as described earlier. Rain that falls this way in torrents is more destructive than the gentler rain of temperate zones. More is lost in runoff and less filters into the ground.
Yet water management is less advanced in Sub-Saharan Africa than in any other developing region, including Africa north of the Sahara where water management is more developed. In Sub-Saharan Africa, almost half of the irrigated area is concentrated in two countries only: the Sudan and Madagascar. In the rest of the region, irrigated land is only about 2 per cent of the cultivated area. This compares with 8.5 per cent in Latin America and 29 per cent in Asia (Harrison 1987).
Most of the large-scale irrigation schemes and soil conservation work tried out in Sub-Saharan Africa in the past have met with little success. As Critchley (1991) points out, concern about soil conservation is nothing new in Africa. Several colonial administrations recognized from the early part of the twentieth century that there was an erosion problem. Programmes of one sort or another continued in most countries until independence. But the majority of these schemes were resented by the local people, who were forced to supply labour.
However, the cycles of drought that have affected Sub-Saharan Africa in recent decades have drawn renewed attention to the role of soil and water management in ensuring crop production in semi-arid lands. The need for conservation programmes is much greater now, because of population increase, than when the first unpopular programmes were started. However, new approaches need to be developed to avoid the many mistakes of the past.
The way ahead: How to make every drop count
At least two major lessons can be learnt from past failures (Critchley 1991): first, for subsistence farmers, the idea of preventing future loss of soil is irrelevant to present pressing needs; and, secondly, the farmers themselves have, in the past, simply not been consulted about their knowledge and understanding of the processes of erosion. Both traditional technologies and social organizations have usually been ignored.
The way ahead calls for alternative strategies to large-scale conventional irrigation schemes or soil and water conservation projects. One such alternative being implemented with success in the Sahel is a low-cost water-harvesting technique adapted by incorporating a traditional practice, in Burkina Faso, of placing lines of stones to slow down runoff. But slopes in the Yatenga region where the project was developed are too gentle (between 0.5 and 2 per cent) and levels are impossible to get right by eye, although runoff erosion is quite severe. In response to this constraint, the Oxfam project devised an inexpensive (and rather ingenious) tool: the water-tube level, which accurately identifies the contour lines. Originally developed in the arid Negev desert 3,000-4,000 years ago, the water-harvesting technique is now being tried out with various adaptations in many parts of the Sahel, and is now widely adopted by farmers in the Yatenga region in Burkina Faso (Wright and Bonkoungou 1985; Younger and Bonkoungou 1989; Critchley 1991). The success of the technique has exceeded expectations.
In the course of four to five years, the Oxfam project perfected a traditional technique into a now highly valued water-harvesting technology that successfully collects water and holds it on the field, preventing soil erosion and increasing water infiltration and crop yields. Thousands of farmers now use the technique, and the number is growing rapidly as others observe its success. Scientists are now studying the possibility of using agro-forestry technologies to improve the technique even further by planting suitable trees and shrubs along the contour lines.
Supplementary irrigation and rain harvesting are a useful way to increase the water available to crops. However, Cooper and Gregory (1987) indicate that this is only one of many ways to make every drop count. They point out that in rain-fed farming systems, where lack of moisture limits crop production, agronomists frequently assess innovative management practices in terms of water use efficiency, which is the ratio of dry matter produced to water used for the production of that dry matter. This is expressed in units of kg/ha/mm and can be increased either by increasing total water supply, as in the case of the water-harvesting technique described above, but also by increasing transpiration efficiency or by reducing evaporation from the soil surface, e.g. through mulching. In terms of water conservation, the principal effect of mulching is to reduce soil evaporation. This is often complemented by many other beneficial effects. In the acid sandy soils (Psammentic Paleustalfs) of the Sahelian zone in West Africa, Kretzschmar et al. (1991) report that crop residues play a key role in increasing pearl millet (Pennisetum glaucum L.) yield, a beneficial effect likely due to improvement of P nutrition through both an increase in P mobility in the soil and enhancement of root growth. Although alternative uses of crop residues for fuel and animal feed limit their availability as mulch, the development of agroforestry techniques could make leaves and small branches of multipurpose trees available for mulching, a traditional practice known to small farmers in the rain-fed agriculture region of the West African Sahel.
The success of the water-harvesting technique demonstrates that a project that proceeds with a low budget and pursues a low-technology method can yield significant returns. Of course, this does not imply that all agricultural research should follow such a strategy - many high-technology projects have also yielded high rates of return - but it does suggest that a place exists for simpler technological changes, and that planners should not forget them. Small-scale measures on a large scale could be a viable alternative to the large-scale projects that so conspicuously failed in the past.
"Sustainability" and "sustainable development" have become the key terms in addressing the world's general concern over environment and development issues. In Sub-Saharan Africa, the development process seems to have reached an impasse. Food production per person has declined steadily during the past three decades. People in many countries of the region are poorer now than they were 30 years ago around the period of independence. The environmental crisis is equally tragic and plagued by desertification and recurrent droughts in the semi-arid lands and high rates of deforestation in the humid eco-zones.
Scattered in the gloomy picture, however, some success stories offer useful lessons and point to the direction that could lead to sustainable development in Sub-Saharan Africa. This paper has underlined the potential of agro-forestry and a small-scale water-harvesting technique to combat desertification and promote sustainable agricultural production. These alone would not be enough to reverse the current negative economic growth of Sub-Saharan Africa. Without them, however, it appears that sustainable agricultural development in the region could remain an insurmountable challenge for the near future.
I gratefully acknowledge the help received from Dr. Peter Cooper and Chin Ong at ICRAF, Dr. Joseph Menyonga at OAU/STRC-SAFGRAD in Ouagadougou, and Professor Bakhit, University of Khartoum.
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