El Nino and Global Grain Supplies

by Teresa Acklin
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An agricultural meteorologist examines the 1997 El Nino — a major episode of ocean warming — and its possible effects on grain production and supplies.

By Kevin Marcus

   In March 1997, an El Nino began forming rapidly and by mid-year already had reached a magnitude matching the intensity of strong El Ninos experienced in 1957, 1972 and 1982. The situation prompted the U.S. National Climatic Prediction Center to post an “El Nino advisory.”

   An El Nino gets its name from the warm ocean current flowing southward along the coast of Ecuador and Peru. Many years ago, local residents called this annual current “El Nino,” Spanish for “the child” or Christ child since it normally appears around the Christmas season.

   In some years, a much larger or more extensive warming of the Pacific Ocean occurs, including the central and eastern equatorial Pacific Ocean. Today, the term “El Nino” is applied to these major episodes of ocean warming, which recur about every two to seven years.

   A La Nina is the reverse of an El Nino and occurs when the warmer equatorial currents fail to appear or are weaker than normal. La Ninas are referred to as “cold” events.

   El Nino and La Nina episodes make up the seesaw cycle of changing air pressure patterns termed the Southern Oscillation. It is unknown what initiates these episodes, but the following chronology of events is usually observed as an El Nino develops:

   • air pressure rises in the western equatorial Pacific;

   • trade winds weaken;

   • cold water upwelling along the equatorial Pacific decreases, resulting in warmer than normal sea surface temperatures; and

   • rains increase over the area of warmer water, increasing the strength of the Pacific storm track.

   The map above shows the area of consistent precipitation anomalies in an El Nino event. The reverse precipitation patterns occur in these same areas in a La Nina event.

   Volcanic eruptions appear to play a role in the strength of an El Nino event. For example, in 1991, the eruption of Mount Pinatubo in the Philippines set off a chain reaction resulting in weak to moderate El Nino conditions in 1991 and 1992. No significant volcanic activity has been observed in 1997, but the sharp changes still occurring in the world's weather pattern may be related to the after-effects of Mount Pinatubo.

   The strength of the El Nino event typically is measured by the departures from normal in air pressure, sea surface temperatures, strength or weakness in the trade winds and amount of cloud cover over the warmer tropical waters of the Pacific. A comparison of 1997 measurements with those of three other years when strong El Nino events developed indicates we are headed for one of the strongest El Nino events of this century.

   Except for a major volcanic eruption such as Mt. Pinatubo, no other force in nature has the global impact on short term weather patterns as an El Nino. While longer term climate changing features such as global warming continue, it has been the El Nino/La Nina events that have been linked to significant season-to-season variations of the weather.

   In the United States, the highest correlation between the Southern Oscillation and weather is for the development between October and April of a mild, wet pattern over the central U.S. and cool, wet weather in the south and southeast during an El Nino.

   Statistics show that during El Nino years, U.S. crops normally have above-trend line yields; conversely, during La Nina years, maize, wheat and soybean yields tend to fall below trend lines. This relationship appears to stem from moisture surpluses developed from October to April in El Nino years and moisture deficits in the same period in La Nina years.

   Other grain and oilseed producing areas to watch over the next six to nine months for reduced crops because of drought are generally within 35° of the Equator and include wheat in Australia, wheat and groundnuts in India, maize in South Africa, palm oil in Malaysia, copra in the Philippines and maize and soybeans in China.

   Australian wheat and South African maize areas often are devastated by drought in El Nino years. (See accompanying article.) A weak Indian monsoon can result in spotty rains and an early retreat, resulting in short moisture supplies for groundnuts and soybeans in the north and reduced irrigation water supplies for winter wheat.

   Dryness in northern China does reduce dryland summer crop production, but the majority of the maize and soybean crops can be irrigated, minimizing the drought's impact. In Malaysia and the Philippines, tropical oil production is likely to be impacted in 1998 because of dryness during the second half of 1997.

   In South America, excess rainfall in Argentina and southern Brazil between September and December can delay and reduce the quality of the wheat harvest and slow soybean and sunflower planting. Wet weather in these areas tends to enhance the growth and development of soybeans, sunflowers and maize.

   Since a strong El Nino already has developed, we can already anticipate the impact on ending stocks of wheat, maize and soybeans in 1997-98. In general, we expect to see some increase in world maize and soybean stocks on the strength of U.S. production, but world wheat stocks are likely to fall.

   In any case, the world ending stocks of each of these commodities are expected to remain tight going into 1998 and 1999. This forebodes continued commodity price volatility, especially considering that there is an increased possibility of drought in major grain and oilseed areas in either 1998 or 1999.

   Kevin Marcus is an agricultural meteorologist with Earth Satellite Corporation's CROPCAST Services, Rockville, Maryland, U.S.

El Nino takes bite out of forecast wheat yields for Australian crop

   Development of an El Nino weather pattern has lowered the forecast for Australian wheat yields by 29% from the record 2.08 tonnes per hectare garnered last year. The Australian Bureau of Agricultural and Resource Economics in its crop report released July 2 forecast Australian wheat yields in 1997-98 to average 1.46 tonnes per hectare.

   ABARE earlier had reduced its projection of 1997-98 Australian wheat production to 16.235 million tonnes from the 19.2 million forecast before the onset of the El Nino event, which would be down 7.341 million tonnes, or 31%, from an estimated record output of 23.586 million in 1996-97.

   The production and yield forecasts assumed a drier than average year, but no severe drought of the type that had occurred in 1982-83 and 1994-95, when average yields across Australia had been only 0.77 and 1.11 tonnes per hectare, respectively, stated ABARE.

   “The average Australian wheat yield for 1997-98 is forecast to be 29% below last year's record level,” said ABARE. “However, it is only 15% below the long-term average, a figure consistent with an average of past El Nino events. By way of comparison, in 1994-95, wheat yields were 35% below average, and in 1982-83, they were more than 50% below average.”

   While the ABARE report referred to a June 3 statement by the Bureau of Meteorology's National Climate Centre to the effect that the El Nino pattern would persist for the remainder of 1997 and was likely to strengthen, it pointed out that a large variation in yields still could be expected.

   “With timely rains, above average yields can be achieved during years with below average rainfall. The timing and amount of rainfall over the next few months will, therefore, be critical in determining the extent to which the current El Nino weather pattern will affect the yields ultimately achieved.”