What is El Niño?

The term El Niño (Spanish for "the Christ Child") refers to a warm ocean current that typically appears around Christmas-time and lasts for several months, but may persist into May or June. The warm current influences storm patterns around the globe. As a result, these "El Niño" climatic events commonly cause bring heavy rains and blustery storms, and drought. Basically, the warmth normally seen in the Pacific Ocean near the southwest Pacific spreads toward the center of the ocean during an El Niño. The warm water carrries with it rain stroms that would typically hit Australia and parts of the western Pacific.

The current El Niño will probably surpass the greatest El Niño of century, that of 1982-83. During the past 40 years, nine El Niños have affected the western coasts of North and South America. Most of them raised water temperatures along 5000 miles of coast. The weaker events raised sea temperatures only a few degrees Fahrenheit and caused mild changes in weather. But the strong ones, like the El Niño of 1982-83, left a climatic imprint that was global in extent.

El Niño recurs irregularly, from two years to a decade, and no two events are exactly alike. Before the 1982-83 El Niño event, scientists did not collect detailed information on El Niños, so information is scanty for making high-quality predictions about the effects of the current El Niño of 1997-98.

The impacts of El Niños can be devastating, as illustrated by some of the effects of the unusually strong El Niño of 1982-83:

• Drought (sometimes with associated wildfires) in many nations (particularly in the western Pacific Rim, southern and northern Africa, southern Asia, southern Europe, and parts of South and Central America)
• severe cyclones that damaged island communities in the Pacific
• flooding over wide areas of South America, western Europe, and the Gulf Coastal states
• severe storms in the western and northeastern United States.

Effects of the 1982-1983 El Niño

The 1982-1983 El Niño is the largest well-studied El Niño event, and it had dramatic effects on millions of people. In Ecuador and northern Peru, up to 100 inches of rain fell, transforming the coastal desert into a grassland dotted with lakes. Lush vegetation disrupted populations of many animals, from grasshoppers to toads, birds, and fish. The disruptions had both beneficial and destructive consequences for the people of the region. For example, some flooded coastal estuaries set shrimp production records, but also set records for the number of mosquito-borne malaria cases.

In North America, winter storms battered southern California and caused widespread flooding across the southern United States, while northern ski resort owners complained of unusually mild weather and a lack of snow. Inland lakes rose and flooded communities and roads. Landslides destroyed homes and killed people. Rivers flooded and destroyed parts of cities.

Overall, the loss to the world economy in 1982-83 as a result of the climate changes amounted to over $8 billion. The toll in terms of human suffering is much more difficult to estimate.

El Niño events over the last 40 years
El Niño warmings (red) and La Niña coolings (blue) since 1950. Source: NOAA Climate Diagnostics Center

What are landslides, debris flows, mudflows, and flash floods?

Examples of El Niño storm effects in the desert southwest

Examples of El Niño storm effects in coastal southern California

For further information, contact David Miller

http://geology.wr.usgs.gov/wgmt/elnino/what.html, 30 November 1999