South America:
Climatic Regions and El Niño
South America's climate exhibits great variety, from the driest desert in the world to the world's largest tropical rain forest. It also includes tropical, as well as, subtropical areas. Finally, strong altitudinal zonation occurs with each altitudinal zones displaying distinct local climates, soils, crops, domestic animals and modes of life.
Tropical Areas
Altitudinal Zonation
Outside the Tropics
El Niño
Tropical Areas [wwtropic]
"Tropical" means that the location is between the Tropic of Cancer and the Tropic of Capricorn. Much, but not all, of South America lies in the tropics. Climates [smclimat] found here include Af, Am, Aw, BW, BS and the H (highland) climates of the Andes.
Rainy Tropical Areas (Af and Am) [smclia]
Wet-Dry Tropical Areas (Aw) [smclimaw]
Dry areas (BW and BS) [smclimb]
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Altitudinal Zonation
[large: altzona]
[small: altzonsm]
Altitudinal variations (mountains) in tropical areas have a significant impact on the local climate resulting in climatic zones that correspond with elevation. This zonation of climate according to elevation is called altitudinal zonation. Each zone has its distinctive climate, vegetation, agriculture, and therefore lifestyles.
Physical geographers have named these climatic zones. Different authors sometimes differ slightly in their terminology and characteristics, but they all describe the effects of a 3.5 degree Fahrenheit drop in temperature that occurs with every 100 foot increase in elevation.
The mountains of the "Ring of Fire" [ringfire] found in Middle and South America exhibit these altitudinal zones [mmclimat] [smclimat].
In equatorial areas geographers describe five altitudinal climatic zones:[large: altzona] [small: altzonsm]
Further north or south from the equator, the elevations of each
altitudinal zone declines.
[large: altzona]
[small: altzonsm]
tierra caliente
The lowest vertical zone from sea level to 2,500 feet, is known as the tierra caliente or the “hot” of the coastal plains and low lying interior basins where tropical agriculture (such as bananas) predominate.
tierra templada
Above this lowest zone lie the tropical highlands containing Middle and South America’s largest population clusters, the tierra templada of temperate land reaching up to 6,000 feet. Temperatures in this region are cooler; prominent among the commercial crops is coffee while core (maize) and wheat are the staple grains.
tierra fria
Still higher, from about 6,000 feet to nearly 12,000 feet is the tierra fría, the cold country of the Andes where crops such as potatoes and barley are the mainstays. Only small parts of Middle America reach into this zone, but in South America this environment is more extensive in the Andes.
puna
Above the tree line, which marks the upper limit of the tierra fría, lies the puna (or paramos); this extends from 12,000 to 15,000 feet and is so cold and barren that it can support only the grazing of sheep and other hardy livestock.
tierra helada
The highest zone of all is the tierra helada or “frozen land”, a land of permanent snow and ice that reaches to the peaks of the highest mountains. As one moves poleward of the tropics beyond 15 degrees of latitude, the sequence of these environmental zones extends downward with breaks occurring at progressively lower altitudes.
For more on altitudinal zonation you may want to review the lecture from the Middle American realm.
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Outside the Tropics (Sub-Tropical)
"Tropical" [wwtropic] means that the location is between the Tropic of Cancer and the Tropic of Capricorn. Much, but not all, of South America lies in the tropics. A small part of southern South America lies in the subtropics (outside the tropics). Here you'll find the populated [smecumen] [smpopden] C climate areas [smclimat] of the Argentine Pampa [smphys] and the drier BW [smclimat] and the arid BS climate of Patagonia.
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El Niño [smelnino]
Of South America’s environments, none is more unique than the Atacama Desert. From coastal Equador to middle Chile, the west coast of South America is very dry [smprec], and from Southern Peru to Northern Chile which constitutes the Atacama Desert, this region is the driest region in the world. Little annual precipitation occurs in this desert because of the cool ocean currents [smcurrnt] and because the region lies in the extremely dry rainshadow of the Andes Mountain Range. These cool ocean waters provide Peru with one of the richest fisheries in the world. Abundant populations of anchovies and tuna are found in nearby waters which provide Peru with valuable exports. This industry is also supported by cold bottom upwelling waters. Every few years, however, the water becomes warmer, the winds reverse and the ecosystem is damaged by El Niño (receiving this name because of an annual warming that occurs during Christmas). However, periodically this phenomenon [smelnino] becomes stronger than normal commencing during the spring, reaching its peak during the following winter and declining during the next spring. What is now known is that El Niño is part of a complex ocean-atmospheric system which is a part of the world-wide climate.
As previously stated, the cold Peruvian (or Humbolt) Current [smcurrnt] flows equatorward along the coast of Ecuador and Peru. This flow encourages upwelling of deep, nutrient-filled waters that serve as the primary food source for millions of fish, particularly anchovies. In addition to sustaining the local fish industry, these fish support a large population of birds whose droppings (guano) are mined and exported as fertilizer. Near the end of each year, a weak, warm countercurrent flows southward along the coasts of Ecuador and Peru, replacing the cold Peruvian current. Normally these warm countercurrents last for a few weeks when they again give way to the cold ocean current. However, every three to seven years, this counter-current is unusually warm and strong. Today the term El Niño (or ENSO for El Niño Southern Oscillation ) is used to describe these episodes of ocean warming that greatly exceed the relatively weak event that originally bore the name. The onset of El Niño is heralded by the appearance of a warm pool of water in the central and eastern Pacific, and a falling of barometric pressure in the same region. This see-saw pattern of atmospheric pressure between the eastern and western Pacific is called the Southern Oscillation. Each time an El Niño occurs, the barometric pressure falls in the eastern Pacific [smwor] while it rises in the western Pacific near Indonesia and Australia. The rise in air pressure results in generally fair weather (which leads to drought) while the lower pressure regime in the eastern Pacific leads to precipitation and storms. This swing between high and low pressure between these regions is called the Southern Oscillation and the entire phenomenon is called El Niño/Southern Oscillation or ENSO.
Winds in the lower atmosphere are the link between the pressure change associated with the Southern Oscillation and the extensive ocean warming associated with El Niño. During a typical year, the trade winds converge near the equator and flow westward toward Indonesia. This steady westward flow creates a warm surface current that moves from east to west along the equator. The result is a piling up of a thick layer of warm surface water that produces higher sea levels in the western Pacific, with corresponding lower sea levels in the eastern Pacific.
When an El Niño commences, pressures rise in Indonesia while they fall over the eastern Pacific. This causes the pressure gradient along the equator to weaken or to reverse. As a consequence the trade winds diminish and may even change direction. This reversal creates a major change in the equatorial current system with warm water flowing eastward. This eastward shift of the warmest surface water marks the onset of El Niño and sets up changes in atmospheric circulation that affects areas outside the tropical Pacific.
The effects of El Niño are variable, depending in part on temperatures and size of the warm pool. However, some locales are affected consistently by El Niño. In the northern United States and Canada warmer than normal winter temperatures occur (El Niño usually peaks during the northern hemispheric winter). Normally arid portions of Peru and Ecuador experience flooding rains. Above normal rainfall and cooler than normal temperatures occur along the Gulf Coast and Florida. Drought conditions occur over Indonesia and Australia and fewer than normal hurricanes are found in the Atlantic Basin. The recent El Niño is considered the strongest since 1982-1983 (which caused over $13 billion dollars in damage) and many of the above impacts have indeed occurred. In fact the winter of 1997-1998 is the warmest (so far) on record for the entire United States.
[The text of the above information on El Niño was written by Scott Girhard, San Antonio College from his online course GEOG 1301 World Geography. Used with permission.]
For more information on El Niño you may want to go to: http://www.pmel.noaa.gov/toga-tao/el-nino/la-nina-pacific.html
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