What is El Nino? - Definition & Effects

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  • 0:00 Definition of El Nino
  • 1:38 Storm Effects
  • 2:40 Drought Effects
  • 3:02 Prediction
  • 3:36 Lesson Summary
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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

El Nino is a weather phenomenon caused when warm water from the western Pacific Ocean flows eastward. In this lesson, we'll see how the effects of El Nino can be noticed in many parts of the world, with different regions experiencing varying weather anomalies.

Definition of El Niño

When we notice different weather patterns, we usually think of what's in the air. But did you know that a lot of what happens in the air is because of the temperature of the oceans? El Niño is an abnormal weather pattern caused by the warming of the Pacific Ocean near the equator, off the coast of South America. The sun warms the water near the equator, which can make more clouds and, therefore, more rain. However, normally there are trade winds, which blow that warm water west. During El Niño, though, those trade winds weaken, or even reverse, which lets the warm water that is usually found in the western Pacific remain or flow east. This warm water displaces the cooler water that is normally found near the surface of the eastern Pacific, setting off atmospheric changes that affect weather patterns in many parts of the world.

A temperature increase of least 0.9 F (0.5 C) needs to occur in the waters of the eastern Pacific Ocean near the equator for it to be considered an El Niño year. Although El Niño does not occur in a perfectly regular pattern, it seems to happen every 2 to 7 years. Following an El Niño, an opposite phenomenon occurs, called La Niña. During La Niña, the eastern Pacific Ocean experiences cooler than normal temperatures around the equator.

The effects of El Niño are strong and can wreak havoc on weather systems around the world. The changes vary drastically around the globe.

Storm Effects

Along the Pacific coast of the Americas, El Niño can cause severe storms and flooding. Peru and Ecuador usually receive the brunt of the force of El Niño. During the months of April - October, this area experiences increased rain fall. El Niño's effects are not only felt through rain. In normal years, along the coast of Peru, cool, nutrient-rich water is pushed up from the deep waters off the Pacific coast, and this nutrient-rich water is a food source for marine life. However, during an El Niño year, this cold water is replaced by warmer water that lacks those important nutrients. The nutrient-deficient water starves the bottom of the food chain and the effects cause a die-off of larger fish.

El Niño is not all bad in the Americas, though. Away from the Pacific coast, North America actually tends to have milder winters during El Niño years, and it is even thought that El Niño reduces the number and intensity of hurricanes in the Atlantic.

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