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Farmers prepare for drought after Nasa satellites spot early signs of El Niño event

Cattle grazing in a field.

Picture: Itumeleng English/African News Agency (ANA) Archives

Published May 25, 2023


Kelvin waves, a potential precursor of El Niño conditions in the ocean, are moving towards the coast of South America across the equatorial Pacific.

Recent sea level data from the US-European Sentinel-6 Michael Freilich satellite indicate the emergence of El Niño in the equatorial Pacific Ocean.

The data indicates that Kelvin waves, which are approximately 5-10cm tall and hundreds of miles broad at the ocean's surface, are moving from west to east along the equator towards the west coast of South America.

When they form at the equator, Kelvin waves transport heated water from the western Pacific to the eastern Pacific, which is associated with higher sea levels.

A series of Kelvin waves beginning in the spring is a well-known indicator of an El Niño, a periodic climate phenomenon that can influence global weather patterns.

Along the western coasts of the Americas, it is characterised by higher-than-average sea levels and ocean temperatures.

Warmer waters tend to have higher sea levels because water expands when heated. El Niño is also associated with diminished trade winds. The condition can bring milder, drier weather to the south-western US and drought to western Pacific nations such as Indonesia and Australia.

The April data from the Sentinel-6 Michael Freilich satellite indicates that the equator and the west coast of South America have comparatively elevated and warmer ocean water. Warmer waters tend to have higher sea levels because water expands when heated.

The satellite data from Michael Freilich cover the time period between the beginning of March and the end of April in 2023. By April 24, Kelvin waves had accumulated heated water and higher sea levels off the coasts of Peru, Ecuador, and Colombia.

Satellites like Sentinel-6 Michael Freilich can detect Kelvin waves using a radar altimeter, which measures the height of the ocean's surface using microwave signals. When an altimeter passes through warmer-than-average regions, the data will indicate higher sea levels.

"We will be keeping a close eye on this El Niño," says Josh Willis, a Nasa Jet Propulsion Laboratory project scientist.

The National Oceanic and Atmospheric Administration (NOAA) of the US and the UN World Meteorological Organisation (WMO) have recently reported an increase in the likelihood that El Niño will develop by the end of the summer in the northern hemisphere.

In the coming months, continued surveillance of ocean conditions in the Pacific by instruments and satellites should assist in determining its potential strength.

"When we measure sea levels from space using satellite altimeters, we know not only the shape and height of water, but also its movement, like Kelvin and other waves," says Nadya Vinogradova Shiffer, Nasa programme scientist and manager for Sentinel-6 Michael Freilich.

Ocean surges circulate heat around the globe, delivering heat and moisture to our coastlines and altering the weather.

El Niño is the warming of ocean currents off the South American coast in December, which causes below-normal rainfall patterns and higher-than-normal temperatures in certain regions of the globe, including southern Africa, which is often severely affected by drought.

Enso, also known as El Niño & La Niña (El Niño-Southern Oscillation), is a naturally occurring phenomenon characterised by oscillating ocean temperatures in the equatorial Pacific. La Niña, which means “the lady” in Spanish, is the opposite of El Niño.

La Niña is the cooling of sea-surface temperatures in the equatorial Pacific Ocean, which influences atmospheric circulation and, as a result, causes a period of above-average precipitation and below-average temperatures.

The world is currently coming out of a La Niña event. The pattern can fluctuate irregularly every two to seven years, with each phase causing predictable temperature, precipitation, and wind disturbances.

These alterations disrupt the large-scale air circulation in the tropics, causing a succession of global side effects.

El Niño and La Niña have the greatest effect on the global climate during the winter in the northern hemisphere. If an El Niño event develops as predicted, the world will experience a period of exacerbated warming, with southern Africa bearing much of the brunt of low rainfall and extensive drought conditions.

Brace yourselves for above-inflation food price increases from the beginning of 2024 onwards as farmers count the cost of low harvests and increased input costs.