The El Niño phenomenon is associated with unusually warm surface waters in the tropical and equatorial regions of the eastern Pacific Ocean. During normal, non-El Niño conditions, the trade winds blow westward across the tropics, piling up warm water in the western Pacific. Under normal conditions, the water surface in the western Pacific is approximately 1.5 ft higher than in the eastern Pacific. The warm surface water creates a naturally rainy environment in this region, especially along the eastern coast of Indonesia.
El Niño (warm) and La Niña (cold) graphics show change in degrees Celsius (scale on right) from normal sea-surface temperatures (image credit: USGS and NOAA). [larger version]
During El Niño conditions, the trade winds relax, allowing the warm water to flow eastward across the Pacific Ocean. The increase in water temperature in the eastern Pacific fuels an increase in storms and rainfall along the coastlines of Ecuador, Peru, and the southern United States. The increase in rainfall often leads to landslides and the failure of coastal cliffs. Additionally, the increase in storms generates large waves that attack the coastline with a greater frequency than during non-El Niño years. During the severe El Niño events of 1982-83 and 1997-98, extensive coastal erosion was recorded along the western coast of the United States.
Scientists do not currently understand how El Niño forms, although much attention and research is focused on this important concept. The occurrence of El Niño has great implications on the global weather system, causing droughts in Indonesia, warmer than usual temperatures in western Canada, and increased rainfall in the Gulf of Mexico. Additionally, during El Niño years, hurricanes are more frequent in the Pacific Ocean and less frequent in the Gulf of Mexico and Atlantic Ocean. In contrast, the occurrence of La Niña, which is the cooling of the equatorial Pacific, coincides with an active hurricane season in the Atlantic Ocean.
return to Extreme Storms Overview | continue to Storm-Induced Coastal Change Overview