A worldwide drought in 1972 and 1973 precipitated food shortages and a rise in food prices in several regions of the world.
During 1972 and 1973, many regions of the world experienced one of the most severe droughts of the century. Particularly severe conditions affected the Sahel of northern Africa south of the Sahara, the Soviet Union, India, China, Australia, and Amazonia. Some areas experienced famine, hunger, and starvation, whereas others suffered only crop shortages but had to import foodstuffs, causing prices to rise worldwide.
Drought is difficult to define, as are its specific causes. In general, a region that experiences subnormal precipitation over an unspecified period of time can be said to be suffering from drought. The events that caused the global drought of 1972-1973 occurred throughout the world and resulted in changes to the physical environment, especially the atmosphere, brought about by both natural and human actions. Areas most prone to drought are desert rims and semiarid steppe regions. Precipitation in these areas is unreliable, and even small changes in precipitation can initiate a drought.
Several conditions were cited as causal factors of drought in the early 1970’s. These included a change in the seasonal position of the Intertropical Convergence Zone
Studies of the atmospheric circulation showed the existence of two basic climatic regimes that affect the location of the ITCZ and of subtropical highs. The Hadley regime
Poleward of the Hadley regime, the Rossby regime
The southern area of the Rossby regime borders on the subtropical highs that result from subsiding air in the Hadley regime. The highs thus form the junction between the two regimes; the locations of the highs are determined by the temperature gradient between the equator and the poles. These highs restrict precipitation when they are in place.
During the winter, the polar areas are extremely cold, whereas the tropical temperatures vary little from the warm season to winter. As a result, the temperature gradient between the equator and the poles is greatest during winter. The Rossby regime consequently dominates in winter and pushes the Hadley regime, with its subtropical highs, further toward the equator over the drought-sensitive areas.
In the summer, the temperature gradient is less than in the winter, so the Rossby regime migrates poleward. The subtropical highs and the ITCZ also migrate poleward. The significance of these migrations is the location of the junction between the two regimes. When the subtropical highs move poleward, the ITCZ moves poleward as well. Thus the position of the subtropical highs determines the poleward extent of the rain-bearing ITCZ. A one-third-degree equatorward change (36 kilometers) in the Atlantic High has been known to cause a latitudinal change of one degree of latitude of the ITCZ.
Vertical temperature gradients are also known to have an effect on the location of the ITCZ. Studies indicated that a 0.06-degree increase in temperature per kilometer can also cause a one-degree shift in the ITCZ. Pollution, in the form of carbon dioxide in the atmosphere, enhances the greenhouse effect as the quantity of this gas increases and temperatures in the industrial middle latitudes also rise. It was thought likely that carbon dioxide affects only temperatures near Earth’s surface, not those aloft. A change in surface heating affects the vertical temperature gradient, however, which in turn influences the location of the subtropical highs.
Pollution in the form of particles affects the horizontal temperature gradient, which can also affect the position of the ITCZ and subtropical highs. Particles affect temperature by reflecting and scattering incident solar radiation, thereby lowering the surface temperature of Earth. Research showed particle concentration to be greater in high latitudes, which results in a stronger temperature gradient between the equator and the poles in summer. The larger gradient in turn affects the positions of the ITCZ and subtropical highs, much as the winter gradient does.
In areas with monsoons, rainfall is heavy, but it is neither constant nor uniform from one year to the next. After the rainy season, June through September, the remainder of the year is dry. The summer precipitation pattern is divided into active and break phases; an active phase is characterized by cloudy skies and copious rainfall, while the break phase is sunny and hot. Years associated with drought usually correlated with a late onset and early withdrawal of the monsoon, as well as insufficient precipitation during the monsoon, particularly if break phases were extended. Crop failure, famine, and starvation could follow.
Aloft, midlatitude westerlies on occasion develop an extreme meridional pattern in which large pools of air are cut off from the main zonal circulation. Air rotating clockwise is a blocking high; this high, because of the jet stream around it, resembles the Greek letter omega, which is why it is called an omega block. A block of this type tends to persist for several weeks or even longer, and since block weather is characteristically hot and dry, drought usually follows. The block deflects cool, humid air far poleward of its usual path, so there is no relief from the hot, dry weather.
El Niño is a warm-water current that periodically—usually every three to seven years—flows southward along the coast of Ecuador. It covers the cold, Peruvian current and prevents upwelling of cold water along the coasts of Ecuador and Peru. El Niño is often associated with the Southern Oscillation,
A combination of the Southern Oscillation and El Niño produces what is called an El Niño-Southern Oscillation (ENSO) event.
Desertification,
The area most affected by the 1972-1973 drought was the African Sahel, a stretch of land from Senegal in the west to Ethiopia in the east. The causal factors here included monsoon failure, expansion of circumpolar westerlies inhibiting the northward movement of the rain-bearing ITCZ, global increase in carbon dioxide, and desertification. In 1972-1973, an estimated 100,000 to 200,000 people and as many as four million cattle died. A mass migration of people fled southward, leaving their homes and at times crossing international borders. Many went to urban areas in search of food and work, only to end up in refugee camps. In Ethiopia, Kenya, and Ivory Coast, the harvest of coffee was reduced. In Nigeria, ground nuts, sorghum, and rice harvests were sharply curtailed. It was also suggested that stresses from famine led to the demise of the imperial regime in Ethiopia. The result of the drought in these areas was catastrophic.
During this period, the Soviet Union also suffered from drought. The cause here was a blocking system, which directed rain-bearing storm systems farther northward than usual. As a result of drought, the 1972 Soviet wheat crop failed, and the country had to import 18 million tons of wheat from the United States, depleting U.S. grain reserves. Forcing the Soviet Union into the international grain market in this way caused the price of wheat to rise sharply, tripling by 1974. The same blocking systems extended the drought into China, where the harvest was described as disastrously short of expectations.
A failure in the monsoon system brought drought to northern India, resulting in crop failures, particularly the grain crops. Monsoon failure could also be blamed for drier conditions in Australia, where wheat harvests were reduced 25 percent below the previous five-year average.
The drought-prone zone of eastern Brazil, Amazonia, suffered when the ITCZ remained in a northerly position and the more stable air of the south Atlantic dominated. The effects of the strong ENSO event were compounded by a descending branch of the Walker circulation covering most of Amazonia. The result was crop failure, particularly a reduction of the coffee harvest, which caused long-term economic problems for the country. The ENSO event also affected Peru and Ecuador by curtailing upwelling of the cold, nutrient-rich waters along the coast, where the anchovy harvest was ruined. Prior to 1972, Peru had harvested between 12 and 14 million tons of anchovies every year, but after 1972 the harvest averaged only about 2 million tons annually.
The Middle East suffered less from drought than most other areas. The yields of wheat—the major crop in this region—were down, but this did not substantially affect the economy, which was based on oil. Perhaps the major impact on this region was the fact that the national leaders realized that oil was not inexhaustible, and that they must be prepared for a time when there was no more oil and another drought occurred.
Long-term effects of the 1972-1973 drought were many. It caused scientists to reassess their interpretation of climate as related to drought and to make efforts to develop methods for predicting drought to help offset the consequences. Confidence in the Green Revolution decreased because the new crops were found to be more susceptible to climatic change than the more traditional varieties had been. The oil-rich nations with little agriculture gained a new appreciation for climatic threats to world food supply and for the need to diversify and strengthen their economies against the time their oil reserves ran out. The U.S. Agency for International Development (USAID) attempted to shorten the response time of international relief organizations and established the Famine Early Warning System
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Bergman, K. H., et al. “The Record Southeast Drought of 1986.” Weatherwise 39, no. 5 (1986): 262-266. Provides some background on a severe drought in the southeastern United States caused by a blocking anticyclone. -
Bryson, R. A. “Drought in Sahelia: Who or What Is to Blame?” Ecologist 3 (1973): 366-371. A good attempt to explain what caused the drought and how humans contributed. -
Bryson, Reid A., and Thomas J. Murray. Climates of Hunger: Mankind and the World’s Changing Weather. Madison: University of Wisconsin Press, 1977. A detailed analysis of drought in relation to climate. -
Geist, Helmut. The Causes and Progression of Desertification. Burlington, Vt.: Ashgate, 2005. Examines the root causes of desertification in 132 case studies. -
Glantz, Michael H., ed. Desertification: Environmental Degradation in and Around Arid Lands. Boulder, Colo.: Westview Press, 1977. An excellent work focusing on the destruction of arable and potentially arable land through drought and desertification in arid and semiarid lands caused by changes in climate and by human activities. -
Harman, Jay R. Synoptic Climatology of the Westerlies: Process and Patterns. Washington, D.C.: Association of American Geographers, 1991. Presents an in-depth analysis of characteristics of the planetary-scale westerlies. -
Knox, P. N. “A Current Catastrophe: El Niño.” Earth 1, no. 5 (1992): 30-37. Describes in detail the oceanic and atmospheric changes during an ENSO event. -
Mortimore, Michael. Roots in the African Dust: Sustaining the Sub-Saharan Drylands. New York: Cambridge University Press, 1998. Proposes an optimistic model of sustainability in Africa and suggests policies that may support dryland peoples.
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