Residents of the southern United States spent December enduring some of the worst floodings in more than decade. In South America, hundreds of thousands of people in the bordering areas of Paraguay, Uruguay, Brazil, and Argentina had to evacuate their homes because of severe flooding in the wake of heavy rains brought on by El Niño.
The U.S. space agency is warning this year’s El Niño could be as powerful as the one in 1997-1998, which led to intense ice storms and flooding across the country.
The conclusions are based partly on new satellite images that show the current El Niño pattern closely mirroring the one from 1997-1998, which was one of the strongest on record.
“The images show nearly identical, unusually high sea surface heights along the equator in the central and eastern Pacific: the signature of a big and powerful El Niño,” NASA said in a statement.
El Niños are triggered when the steady, westward-blowing trade winds in the Pacific weaken or even reverse direction, triggering a dramatic warming of the upper ocean in the central and eastern tropical Pacific. Clouds and storms follow the warm water, pumping heat and moisture high into the overlying atmosphere. These changes alter jet stream paths and affect storm tracks all over the world.
This year’s El Niño has caused the warm water layer that is normally piled up around Australia and Indonesia to thin dramatically, while, in the eastern tropical Pacific, the normally cool surface waters are blanketed with a thick layer of warm water. This massive redistribution of heat causes ocean temperatures to rise from the central Pacific to the Americas. It has sapped Southeast Asia’s rain in the process, reducing rainfall over Indonesia and contributing to the growth of massive wildfires that have blanketed the region in choking smoke.
El Niño is also implicated in Indian heat waves caused by delayed monsoon rains, as well as Pacific island sea level drops, widespread coral bleaching that is damaging coral reefs, droughts in South Africa, flooding in South America and a record-breaking hurricane season in the eastern tropical Pacific. Around the world, production of rice, wheat, coffee and other crops has been hit hard by droughts and floods, leading to higher prices.
In the United States, many of El Niño’s biggest impacts are expected in early 2016. Forecasters at the National Oceanic and Atmospheric Administration favor an El Niño-induced shift in weather patterns to begin in the near future, ushering in several months of relatively cool and wet conditions across the southern United States, and relatively warm and dry conditions over the northern United States. The latest El Niño forecast from NOAA’s Climate Prediction Center is at http://www.cpc.ncep.noaa.gov/
“Looking ahead to summer, we might not be celebrating the demise of this El Niño,” cautioned JPL climatologist Bill Patzert. “It could be followed by a La Niña, which could bring roughly opposite effects to the world’s weather.”
La Niñas are essentially the opposite of El Niño conditions. During a La Niña episode, trade winds are stronger than normal, and the cold water that normally exists along the coast of South America extends to the central equatorial Pacific. La Niña episodes change global weather patterns and are associated with less moisture in the air over cooler ocean waters. This results in less rain along the coasts of North and South America and along the central and eastern equatorial Pacific, and more rain in the far Western Pacific.
El Niño events are part of the long-term, evolving state of global climate, for which measurements of sea surface height are a key indicator.