2.1. What is ENSO?

El Niño \ 'el nee' nyo noun [spanish] \ 1: The Christ Child 2: the name given by Peruvian sailors to a seasonal, warm southward-moving current along the Peruvian coast <la corriente del niño> 3: name given to the occasional return of unusually warm water in the normally cold water [upwelling] region along the Peruvian coast, disrupting local fish and bird populations 4: name given to a Pacific basin-wide increase in both sea surface temperatures in the central and/or eastern equatorial Pacific Ocean and in sea level atmospheric pressure (Southern Oscillation) 5: used interchangeably with ENSO (El Niño-Southern Oscillation) which describes the basin-wide changes in air-sea interaction in the equatorial Pacific region 6: ENSO warm event synonym warm event antonym SEE La Niña \ [Spanish] \ the young girl; cold event; ENSO cold event; non-El Niño year; anti-El Niño or anti-ENSO (pejorative); El Viejo \ 'el vyay' ho \ noun [Spanish] \ the old man

--Michael H. Glantz

Drought in Southern Africa has been associated by several researchers with the recurrent, quasi-periodic appearance of warm sea surface water in the central and eastern equatorial Pacific, generally referred to as El Niño. El Niño is also associated with changes in sea level pressure at locations on opposite sides of the Pacific Basin--called the Southern Oscillation. In the early decades of the 20th century, Sir Gilbert Walker identified a see-saw pressure pattern between Darwin (Australia) and Tahiti. When pressure is high in Tahiti, it is low in Darwin and vice versa. These two natural processes--El Niño and the Southern Oscillation--combine to form ENSO. The occurrence of extreme, cold sea surface temperatures in the central and eastern equatorial Pacific are referred to as cold events or La Niña. Together, cold and warm events make up the ENSO cycle. In this report, ENSO or El Niño will refer to warm events, unless explicitly noted otherwise.

ENSO warm events recur on average every 4 1/2 years with a range between 2 and 10 years. Events have been classified as weak, moderate, strong and extraordinary. The size of an ENSO is determined by several factors: increase in sea surface temperature above normal in the eastern equatorial Pacific Ocean; spatial extent of the warmed surface water, duration of sea surface temperature increase, extent or worldwide societal disruption. Some of these events (moderate to extraordinary) have a major impact on the global climate system disrupting "normal" weather and climate variability, generating extremely adverse meteorological events such as droughts, floods, heavy snowfalls, frosts, etc. These associated anomalies have been referred to as "teleconnections," or linkages over great distances of anomalies.


o Although the reliability of specific teleconnections may as yet be controversial for a variety of reasons, teleconnections can provide policy makers with enough information to "hedge their decisions by." If ENSO events can be forecast some months in advance, societies could prepare to prevent, to mitigate, or to adapt to their impacts.

o Perhaps as important as the ENSO forecast is the ENSO hindcast. ENSO events tend to lock-in at some point in time. Decision makers in countries known to be affected by ENSO teleconnections could benefit from knowledge that an event had begun a few months earlier.

While the equatorial Pacific Ocean constitutes the field of action for ENSO events, their impacts girdle the tropics. ENSO events perturb the atmosphere around the tropics to varying degrees, generating anomalous climatic patterns at the regional and local levels. As a result, we hear about possible connections between an ENSO event and, for example, drought in Northeast Brazil, in Australia and in northeast, east and Southern Africa, the failure of the Indian monsoon, etc. The generalized maps contained in Figure 2.1 suggest possible teleconnections.

Within meteorological circles, teleconnections research has proven useful in aiding the forecasting of possible ENSO impacts around the globe. While interest in teleconnections research has existed for several decades, it was the worldwide devastation associated with the 1982-83 ENSO event (the largest in a century) that sparked heightened research and applications interest in ENSO.

It is important to note that not all societal ills can be blamed on or associated with the occurrence of ENSO events. Although the reliability of specific teleconnections may as yet be controversial for a variety of reasons, teleconnections can provide policy makers with enough information to "hedge their decisions by." If ENSO events can be forecast some months in advance, societies could prepare to prevent, to mitigate, or to adapt to their impacts. It has been demonstrated in countries such as India and Ethiopia, which have drought management systems in place, that advanced warning of the onset of a drought period (in the form of an ENSO forecast) can be very valuable for food security policy making. Such warnings can be used to greatly reduce loss of life, human suffering, and economic losses in severe drought situations (SARDC, 1994).

Perhaps as important as the ENSO forecast is the ENSO hindcast. By this, we mean that ENSO events tend to lock-in at some point in time. Decision makers in various countries known to be affected by ENSO teleconnections could benefit greatly just knowing that an event had begun a few months earlier. Once begun, there is a high probability (but not certainty) that the event will go through its normal life cycle of onset, growth, peak, and decay; and such events usually run for 12 to 18 months.

2.2. ENSO's Impacts in Southern Africa

Several studies have focused on the possible teleconnections between ENSO events in the Pacific and rainfall anomalies in Southern Africa. Tyson (1986; Preston-Whyte and Tyson, 1988) for example, has published several papers on the Southern African link to ENSO events. The World Meteorological Organization Climate System Monitoring report (WMO, 1984) devoted several sections to ENSO and African drought (pp. 7-31). Ogallo (1987) discusses the relationship between ENSO and Southern African drought using the 1982/83 event as an illustration. Rasmusson (1991), in his research on teleconnections, has also noted the ENSO/Southern Africa drought connections. Most recently, Cane et al. (1994) noted a rather strong statistical relationship between Zimbabwean maize yields and sea surface temperatures in the equatorial Pacific. This study came about as a result of a multidisciplinary international "usable science" workshop held in Budapest (Hungary) on the use of ENSO information for food security and famine early warning in sub-Saharan Africa (Glantz, 1994). These studies generally show that, during ENSO episodes, large areas of Southern Africa tend to experience drier than normal conditions.

2.3. Definitions of Drought

o "Drought" has a number of definitions. It is therefore important to distinguish what one means when talking about drought.

It is important to establish a sense of what is meant by the word "drought," for it carries many definitions. Wilhite and Glantz (1985) have grouped droughts into four types: meteorological, agricultural, hydrologic, and socio-economic. While these drought types overlap to some extent, they differ enough to create confusion in the identification of what some may feel is a drought, and others feel is not. Perhaps most crucial is realizing that drought is not just a lack of rain, but can also be defined according to its impacts such as the obvious, most direct effects of drought (withering and/or stunted crops, empty reservoirs, desiccated grazing lands). There are also widespread, costly indirect consequences such as price increases, greater food imports, migration from rural to urban areas, and step-like changes in environmental degradation.

Meteorological drought is often measured as a designated period of time with precipitation less than a specified amount. Such a view considers degree and duration of dryness when compared to a long-term average (called normal). The availability of moisture at different times in the growing season to meet crops' needs is the basis for classifying a drought as agricultural. A hydrologic drought refers to a period when streamflows are unable to supply established users under a given water management system. Socio-economic definitions of drought relate supply and demand of specific goods. A drought-related shortage of food crops, for example, marks a drought condition in the context of human needs. Significantly, humans can create a drought situation through land-use choices or excess demand for water (Glantz, 1994; Wilhite and Glantz, 1985).

While drought itself is aperiodic and unavoidable, its adverse effects penetrate many facets of society such as land quality, acreage planted, export crop acreage, migration, labor supply, urbanization, food imports, and rural poverty (Glantz, 1987). As it gradually worsens, it reveals interdependent socio-economic conditions. The following paragraphs are taken directly from Glantz (1996b) in which the author discusses some aspects of the relationship between droughts, ENSO, food security and society.

Figure 2.2, an idealized version of the agricultural food production system in sub-Saharan Africa, was produced in the early 1980s by the U.S. Department of Agriculture (USDA) for the U.S. Agency for International Development (USAID) to help the agency guide its international food assistance policies. In the lower right hand corner there is a box for weather. Weather, according to this chart, seemingly affects only crop yields. If one were to believe that, one would look for ways to protect crop yields from weather variability (excessive as well as poor rains). For example, a farmer might want to change crop variety to one with a grain that might be less vulnerable to moisture stress. While the chart is a decade and a half old, this narrow view of how climate affects agriculture and related human activities is still widely held.

However, what would happen to the linkages between the weather box and other boxes, if one were to replace the word "weather" with the word "drought"? A drought can affect land quality. Drought combined with poor land use practices, especially in semiarid areas, can initiate or accelerate desertification. A drought can affect on-farm storage, labor migration, the use of inputs such as fertilizers, labor supply, farm income, farmers' skill, imports, and so forth. A more accurate portrayal of how weather in the broad sense (that is, both good and bad weather) can affect food production efforts is depicted in the modified USDA chart shown in Figure 2.3.

Drought can be defined in economic terms as an exogenous supply-side shock which usually causes sharp declines in agricultural output, employment, export earnings, and income levels (Benson and Clay, 1994). Such impacts spread throughout the entire economy by way of sectoral linkages and multiplier effects.

Droughts in Southern Africa

In Southern Africa, the number of meteorological drought occurrences affecting the population has been steadily on the rise. Between 1988 and 1992, over 15 drought events affected at least one percent of various countries' populations in this region, compared to fewer than five such events between 1963 and 1967 (World Conference on Disaster Reduction, 1994). Part of this trend can be tied to increased population growth and cultivation of marginal lands, while another part can be attributed to ENSO-related anomalies.

An index tracking rainfall for Southeastern Africa (bounded by Zimbabwe, Botswana, RSA, and Mozambique) between 1875 and 1978 shows definite variability from year to year, with wet and dry years tending to alternate irregularly. When an ENSO event occurred, there was a strong correlation with subnormal rainfall. During this time there were 24 ENSO events, 17 of which corresponded to a decline in rainfall at least ten percent off of the long-term median (Rasmussen, 1987).

Looking specifically at Zimbabwe's rainfall record this century, the trend indicates a clear increase in occurrences of below average rainfall years, and since the 1960s, a more severe departure of such years from the normal (USAID, 1992). Figure 2.4 shows Zimbabwe's rainfall record from 1980 up to the 1991/92 drought. It should be noted that water is the major limiting factor in Zimbabwe's agricultural production, given that its climate is fairly dry. In any given year, there tends not to be enough rainfall to allow adequate crop production throughout all parts of the country (Bratton, 1987).

Figure 2.4 Zimbabwe's rainfall record, 1980-1993 (From US Mission, 1992)

2.4. Summary

ENSO events are recurrent and quasi-periodic. While their features are generally confined to the Central and Eastern Pacific Ocean, their effects can be felt around the globe in the form of teleconnections. In this regard, ENSO events have been linked to drought in Southern Africa. Drought can be defined in numerous ways; there are agricultural, meteorological, and economic definitions. In the latter half of the twentieth century, Zimbabwe has experienced a large number of meteorological droughts, which in turn has adversely affected its agricultural production.

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