El Nio Southern Oscillation

The El Niño-Southern Oscillation (ENSO) is a large-scale ocean-atmosphere, quasi-regular interaction in the Pacific Ocean, which has reverberations in the climate system worldwide. These climate "teleconnections" bring droughts and floods to many agricultural regions, especially in the tropics, but to some degree in mid-latitudes as well. During an El Niño event, droughts tend to occur in Northeast Brazil, Australia, Indonesia, and southern Africa, among other locations, while floods tend to occur in southeastern South America, the west coast of North America, and the Horn of Africa.

In the La Niña phase, the reverse tends to occur. Figure 10.6 shows the normalized difference vegetation index for southeastern South America under the plentiful rainfall conditions of the El Niño in February 1998, and the severe drought brought on by the opposite La Niña conditions in February 2000. While it is uncertain exactly how a warming climate will affect this major variability system, there is potential for more frequent El Niño-like conditions that may affect agricultural regions around the world (IPCC, 2001).

Figure 10.6 Effects of El Niño-Southern Oscillation on vegetation index in southeast South America: El Niño, February 1998; La Niña, February 2000. (From W. Baethgen, personal communication, 200S.)

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