Managing drought and locust invasions in Africa

Thomas R. Odhiambo

The two most critical African natural disasters - drought and locust outbreaks - are least understood in terms of the four activities considered essential to long-term disaster reduction: hazard prediction, risk assessment, disaster preparedness, and disaster management. In finding a solution to the drought and desertification that plague Africa’s Sudano-Sahelian belt, planners would do well to study indigenous adaptations to the unpredictable Sahelian ecosystem. They should study them, translate them into scientific terms, validate them, and try to implement them to stabilize the Sahelian and other drought-prone ecosystems. The key to solving the problem of locust swarms may lie in the work being done by the International Centre of Insect Physiology and Ecology. ICIPE hopes by studying the behavior of locusts to find a way to dampen the locusts’ swarming cycle and intensify their solitary cycle so that locust populations can maintain a relatively sedentary, grasshopper-like lifestyle. ICIPE hopes that solitary locusts can continue to exist as natural herbivores in Africa’s semiarid breeding grounds, continuing their participation in the dynamics of the savannah ecosystem without periodically breaking into locust plagues.

A.J.W. Taylor (1978) described disasters as “catastrophic events that (a) interfere with everyday life, disrupt communities, and often cause extensive loss of life and property, (b) overtax local resources, and (c) create problems that continue for longer than those that arise from the normal vicissitudes of life.” In this sense, disasters need not be sudden, unexpected, or devastating. Otherwise, disasters such as drought, famine, and epidemics would be excluded. All disasters - industrial or natural - vary in the degree of vulnerability to which victims are subjected and the special attention they require. But disasters caused by the forces of nature are perhaps “the most readily accepted, even if with despair and resignation. They represent the unleashed fury of the natural world against which mankind is quite helpless” (Taylor 1978). This feeling of helplessness has given new impetus to a search for long-range solutions to the management of two pervasive natural disasters in Africa: drought and locusts.

“The true dimensions of poverty are existential rather than economic,” wrote Albert Tevoedjre (1978). To Walter Weisskopf (1989), misery reflected impotence:

The medieval world outlook believes in a supernatural, but comprehensible order. The Newtonian model believed in an order routed in nature and comprehensible through reason. Having abandoned a belief in providence, grace and other worldly rewards for religion’s virtue as well as the deterministic belief in nature and reason, the Heisenbergian paradigm seems to deprive us of all protection against the threat of the unknowable future and of the unknowable reality. (Quoted in Giarini and Stahel 1989.)

The point about such impotence is that people’s traditional, communal ability to cope with recurring setbacks can no longer provide a safety net for victims. They have become more vulnerable, and natural disasters have become an ultimate crisis of destitution. Consequently, more than any other community, Africa’s scientific community today has the responsibility of creating a new perception of natural disasters.

Developing long-range solutions to the two most difficult natural disasters in Africa - drought and locust outbreaks - requires an information-intensive, management-aware strategy. In 1988, the UN Secretary-General appointed an international ad hoc group of experts to recommend a scientific framework for launching the International Decade for Natural Disaster Reduction (IDNDR) for the 1990s. That group considered four kinds of activity essential to a solution-oriented long-range program:

· Hazard prediction through monitoring, early warning systems, and the like.

· Risk assessment - for example, by mapping hazard levels.

· Disaster preparedness, especially by training key personnel, educating the general public, and appropriately controlling land use and construction.

· Disaster management, by developing schemes for local evacuation, establishing lines of emergency supply, and mobilizing civil defense groups.

Drought and locust outbreaks are poorly understood in terms of these four activities. As the group of experts stated in its report:

Drought is a complex environmental phenomenon, including long-term climatological changes and wide-scale ocean/atmosphere interactions as well as ecological deterioration of human origin. The management of drought as a natural disaster has many factors in common with management of disasters of more sudden onset. Drought predisposes the environment to several rapid-onset natural hazards, including locust infestations and, in many instances, flash floods. Drought alone causes large agro-ecological damage and seriously disrupts socioeconomic life. Over this century, droughts have tended to intensify as a result of accelerating deforestation and large-scale soil erosion, especially in Africa; their management globally has become a matter of urgent action.

These catastrophic phenomena now demand a thoroughgoing scientific explanation, leading to solution-oriented technologies that may well incorporate elements of social invention. What Africa needs is to master science and technology, not merely identify with it. This requires that problem-solving become the principal aim of our scientific endeavor focused on drought and locusts. We must become dissatisfied with the existing state of knowledge about these natural processes and events, mistrusting the obvious and searching for the underlying order in natural processes (Sindermann 1985).

Drought in Africa

The Food and Agriculture Organization (FAO) of the United Nations predicts that unless Africa takes corrective action, rainfed croplands on the continent will become 30 percent less productive by the end of the 1990s, mostly because of soil depletion and erosion (World Resources Institute 1989). Part of Africa’s unrealizable potential for agricultural productivity is the 40 percent of the continent that is either extremely arid or subject to cyclical drought.

The Sahara, the largest desert in the world, receives less than 100 millimeters of precipitation a year (Conservation for Development Centre of IUCN 1986). Other arid areas, such as the Kalahari Desert in the south, also suffer chronic low precipitation, usually with high temperatures. Drought, on the other hand, is a temporary feature, experienced only when rainfall deviates appreciably from normal levels (of about 200 millimeters a year). Drought can occur in virtually any rainfall or temperature regime (Lockwood 1988). The Sahel - the zone across the continent south of the Sahara Desert, with annual rainfall of 200 millimeters - has experienced a north-south migration in its 600,000 years of human occupation. The Sahel has now stabilized between 13 degrees north and 19 degrees north, but the research of A.M. Lezine and her colleagues shows that the zone has shifted substantially in the past 20,000 years, a period that has been studied in some detail. Rock paintings show a succession of scenes from game-rich savannah to cattle-herding pastoralists to desert panoramas. Geomorphological and palaeontological evidence in the guise of fossil river systems and drainage networks (for instance, the Wadi Howar system in the Sudan) contains fossil remains of crocodiles, hippos, and river bivalves - in a region that now receives merely 25 millimeters of precipitation a year. Pollen analyses indicate that fossil lakes in the Sahel (for example, the Selima Oasis) once sustained savannah grasslands in areas now hyperarid. These studies conjure an image, some 18,000 years ago, of savannah grassland with scattered acacia trees that extended only as far north as 10 degrees north, which is further south than its current geographical limit. In 8500 before the present (BP), moisture-demanding types of vegetation extended northward rapidly, eventually reaching 400-500 kilometers north of their current agro-ecological limit. Reversal of this northward shift began in about 6100 BP and intensified in about 4500 BP; Sahelian vegetation as we know it today became established in its present zonal limits (13 degrees north and 19 degrees north) about 2,000 years ago.

Despite this volume of evidence, and the more recent episodes of drought in the Sahel during this century - including the great drought of 1984 that caused about 100,000 deaths - we cannot yet predict drought (Conservation for Development Centre of IUCN 1986). We believe that arid lands are rapidly spreading in Africa, often aided by the long cyclical drought periods, based on observations on the fringes of the Sahel and similar semiarid and arid areas such as the Kalahari and Namib Deserts, Somalia, and North Eastern Kenya (UNEP 1985). This aridification, and the rapid deforestation of much of Africa, is leading to three critical phenomena:

· Desertification of the Sahel, through bushfires, overgrazing, increased harvesting of fuelwood, and the spread of cultivation to marginal lands.

· Sahelization of the savannah grasslands.

· Savannahization of the forests.

Desertification has now reached 88 percent in Sudano-Sahelian Africa, 80 percent in southern Africa, and 83 percent in Mediterranean Africa. We cannot yet accurately quantify in time and space the changes associated with desertification, sahelization, and savannahization. Nor are we certain about the factors that determine the onset of drought, although some associations are becoming apparent.

Past studies suggest that drought in Africa south of the Sahara is correlated with (1) drought in the Central America-Caribbean Atlantic region and (2) warm sea-surface temperatures and rainfall on the Pacific coast of Latin America (associated with the so-called El Niffect) - in other words, associating African drought with interactions between the ocean and the atmosphere (Rind and others 1989). Similarly, rainfall in the western Sahel is affected by anomalies in sea-surface temperatures in both the Pacific and Indian oceans. Not that these examples reflect a direct causal relationship. Rather, the droughts over much of the Sahel and North Africa are associated with the reduced (but not delayed) northward extension of the Inter-Tropical Convergence Zone (ITCZ), the band of wet weather that circles the world at the point where the trade winds blowing from the Northern and Southern Hemispheres meet (Rind and others 1989).

For all our ignorance of what causes cyclical drought in Africa, its impact on the human population is profound. The two-decade drought from 1966-67 to 1987 was the worst for 150 years but others almost as bad have occurred every 20 to 25 years or so. Under these circumstances, it is meaningless to speak of protecting the environment. Rather, a way should be found to fit human activities into the reality of the natural systems.

Of the world’s 40 million nomadic pastoralists - whose livestock-based economies survive on deserts or semiarid savannahs - 25 million live in Africa, most now relegated to marginal lands (Bass 1990). Anthropological studies reveal that traditional pastoralists’ knowledge of the environment in which they live and work is highly complex and organized - their plant and animal breeding and husbandry the result of experiential fact-finding that cannot be ignored by modem scientists. According to a Dutch study, quoted by the Independent Commission on International Humanitarian Issues (1985), “traditional herders produce as much protein per hectare as do ranches in areas of equal rainfall in the United States and Australia; the Sahelian herders, however, accomplish this with infinitely less mechanical energy inputs, relying for the most part on manpower.” This husbandry, based on traditional knowledge, requires that the Sahelian herder not stay in one place - lest overgrazing and desertification set in. Settling herders in semiarid areas is therefore often unwise:

Sedentarizing nomads ignores the fact that they employ their marginal resources better than anyone else could. Nomads have lower birthrates than their settled neighbors. Their family herds support more people on the land than do commercial ranches. Nomads make few demands on the state, and they practice the kind of self-sufficiency that any enlightened government should want to encourage (Bass 1990).

Indigenous Sahelian social systems were intimately linked to their agro-ecosystems, until externally imposed changes in recent times led to environmentally destructive change, such as the charcoal production associated with trans-Saharan trade and the expansion of transportation networks (Gritzner 1988). Indigenous adaptations to the unpredictable Sahelian ecosystem - including integrated agro-sylvo-pastoral practices - are not only highly sophisticated but have inherent scientific validity (Gritzner 1988). We would do well to understand them, translate them into scientific terms, validate them, and then try to implement them to stabilize the Sahelian (and other drought-prone) ecosystems.

Desert locust swarms

The Sahel is full of other surprises. One recurrent problem is occasional massive outbreaks of locust swarms. In October 1988, desert locusts (Schistocerca gregaria) bred on an unprecedented scale along much of the Sahel, so that in early October several swarms of them reached the Atlantic coast of West Africa - from Guinea-Bissau in the south to Mauritania in the north - then invaded the Cape Verde Islands on October 5-6 and 12. Soon thereafter, the locusts were sighted over the Atlantic Ocean and began reaching the eastern West Indies from October 14, stretching from St. Croix in the north to the coastal areas of Guyana and Suriname in the south. They made this intrepid landfall 4,500 kilometers from the West African mainland with the assistance of the tropical storm Joan (Rainey 1989).

There are at least five important locust species (and their ecogeographical subspecies) in Africa: the desert locust, the tropical migratory locust (Locusta migratoria migratorioides) found everywhere in Africa and beyond, the red locust (Nomadacris septemfasciata) found in Eastern-Central Africa, the brown locust (Locustana pardalina) found in Southern-Central Africa, and the Senegalese grasshopper (Oedaleus senegalensis) in West Africa and the Atlantic Ocean islands. Undoubtedly, the desert locust is the most intractable, widespread, and perennially destructive of all these pestiferous locusts. There are at least 200 other grasshopper species resident in the Sahel that live normally as herbivores in this savannah ecosystem without swarming as marauding migrants.

In normal years - during the frequent drier periods when the desert locust goes into recession - the species is widely distributed over a wide belt of arid and semiarid lands (including the African Sahel), covering some 16 million square kilometers. Under this recession, the desert locusts live as inconspicuous, solitary grassland herbivores in these semiarid areas. Major locust swarms develop as a result of a rapid increase in locust numbers among the erstwhile recession population when widespread, heavy, prolonged rains occur after a long stretch of drought, in several scattered breeding areas. These wet periods permit two or three generations of the locust to develop in each breeding area, multiplying rapidly - sometimes by a factor of 10⁵. These aggregate, match as hoppers, then swarm as adults, becoming highly mobile and traveling up to 1,000 kilometers a week, assisted by winds. Such gregarious locust swarms arise only after favorable rains, occurring over several seasons, succeed a long stretch of drought years (COPR 1982). The locusts may well invade a much larger area, covering some 29 million square kilometers, taking in all of the Sahel, North Africa, the Mediterranean region, the Middle East, and West Asia.

The old hypothesis that locusts migrate from areas that have become untenable is not correct. The flying locust swarms tend to be carried toward areas where rain has fallen, following the Inter-Tropical Convergence Zone (COPR 1982). The late Reginald Rainey (1989), who made a life-long study of locust migration, concluded, after 40 years studying locust swarming phenomena, that migration is intrinsically adaptive - that locusts use migration as a mechanism to exploit seasonal changes in the spatial distribution of environmental resources. The desert locust simply exploits the necessary environmental resources by becoming airborne, and latching onto the geographically patterned global and local wind systems, which eventually take them to their convergence zones and their rains. The locusts then exploit the ephemeral vegetation, which develops quickly after unusually good rains over an area normally occupied by arid thornbush. This larger invasion area is often even more fragile than the locust’s usual recession breeding area, so the locust invasion wreaks devastation.

The change from inconspicuous, solitary, grasshopper-like individuals (in the drought years) to highly mobile, gregarious, marauding locust swarms (early in the wet years) is associated with a major change in locust behavior, and fairly accurate forecasting systems exist for the appearance of matching hopper bands and locust swarms. The onset of recession - the petering out of locust plagues - is not so simple to predict. We have few clues as to what causes this behavioral change. In 1965-66, desert locust infestations worldwide were at their lowest level in 27 years, and an equally significant 18 years of locust silence followed. Rainey thought that the decline of desert locust infestations in the mid-1960s was associated with “a marked change in the global wind circulation, which had reverted sharply to a type of regime which had prevailed before the 1890s” when desert locust swarms had also been rare. The hypothesis is that these prolonged locust recessions are associated with a shift of the desert zones toward the equator, with equatorial rains (and the ITCZ) more concentrated than before close to the equator (Rainey 1989). It is recognized that these changes do not necessarily entail a direct causal relationship.

The challenge of managing locust invasions

It is a major challenge for the world scientific community - particularly Africans, who have lived with periodic marauding locust swarms for at least 600,000 years, since humans first settled in the Sahel - to begin to manage this natural disaster effectively. It is the belief of the International Centre of Insect Physiology and Ecology (ICIPE) that long-range desert locust management technologies will arise only when scientists know the behavior of locusts intimately and can interrupt mechanisms that regulate such behavior.

Attempts to change the physiology and behavior of the locust between the solitary and gregarious phases are at the heart of ICIPE’s innovative attempts to ground the locust - to make it remain sedentary, behaving as a solitary, grasshopper-like population - and to keep it permanently nonswarming, nonmigratory, and nonmarauding. These efforts, never before tried, are one approach to sustainable management of the desert locust. Other approaches include use of the locust’s natural enemies (including parasitoids and pathogens), the selective use of chemical locusticides, and a more refined locust forecasting and monitoring system. It is ICIPE’s conviction that interrupting the gregarization, the sexual maturation, and the oviposition pheromone systems (which together bring about the rapid and synchronized development of coherent, highly dense locust swarms), together with promoting the solitarization and sexual maturation-inhibition pheromone system (which intensify solitarization), should help locust populations maintain a relatively steady sedentary, grasshopper-like lifestyle. By accomplishing this goal, ICIPE hopes it will help the pheromone-maintained solitary locusts continue to exist as natural herbivores in Africa’s semiarid breeding grounds, continuing their important role as a participant in the dynamics of the savannah ecosystems, without periodically breaking out into locust plagues.