El Niño and La Niña
Objectives
1) To understand the nature of and impact of El Niño and La Niña.
2) To gain an understanding of the interrelatedness of the atmosphere and the oceans.
El Niño and La Niña are excellent examples of the complexity of our atmosphere and its interrelatedness with the oceans of the world.

Overview of El Niño

El Niño is generally thought of as a phenomena that originates every few years off the west coast of South America. In order to understand it, it is useful to review what normally happens in that area in terms of winds and ocean temperatures.

Normal Situation

Off the coast of Peru, the prevailing winds are the SE Trades which help to blow warm water away from the west coast of South America. This allows colder water from below to come to the surface. This colder water contains nutrients which anchovies eat. Therefore, the anchovy industry has been important to the Peruvian economy.

1982: A severe "El Niño" event devastated the Peruvian anchovy industry.

Why?

El Niño appears every few years often around Christmas time as evidenced by the unusual warming of the surface waters near the west coast of South America. As a result of it frequently starting around Christmas, the event has been given the name "El Niño" which means "The Little Boy" or "Christ Child" in Spanish. The warming is due to a weakening of the prevailing winds so that warm water is not blown away from the coast. Rather the water gets warmer and encompasses a larger area. Consequently, the colder water and nutrients from below do not reach the surface.

A Key Understanding

Changes in wind patterns and ocean temperatures in one part of the planet can impact the entire globe's weather.

eg 1982 El Niño:
- severe drought in India and Australia
- large storms struck California
- a milder and drier winter for British Columbia

Winter 1987 and 1998: The largest El Niño event of the 20th Century. Due to better monitoring of ocean temperatures and the use of sophisticated computer models, scientists were able to predict El Niño's arrival several months in advance helping people to prepare.

Overview of La Niña

Every few years, the opposite of El Niño occurs - "La Niña" ("The Little Girl" in Spanish). In this situation, rather than weakening, the trade winds strengthen, blowing more warm water away from the west coast of South America. This allows an unusual amount of cold water to come to the surface. The effects of La Niña are the opposite to those of El Niño so areas that become drier under El Niño become wetter under La Niña. Generally though, the impacts of La Niña are less severe than those under El Niño.

eg the winters of 1998/1999 and 1999/2000: La Niña events
- a wetter winter for BC with more snow in the mountains

Further Information

"Our Complex Atmosphere as Illustrated by an El Niño Event" pages 190 to 192 in Planet Earth: A Physical Geography

El Niño Theme Page
Courtesy NOAA


Assignment Work

1) After reading the information given above, take notes from p.190 to 192 of Planet Earth: A Physical Geography on additional key points regarding this topic.

2) Using the link from above, find out if an El Niño or La Niña event is currently happening or is predicted to occur in the near future.

3) Answer Question #20 from page 192 of Planet Earth: A Physical Geography.
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