GARDEN ROUTE | KAROO NEWS - South Africa has had its first very welcome rains for the 2021/22 rain season in the summer rainfall areas of the country. The grass has greened significantly and the joys of spring are all around to see.
Those involved in agriculture, are always interested in the predicted weather and have probably all seen the longer-term weather forecasts, predicting either a neutral ENSO cycle or a weak La Niña effect.
We all seem to know that this is good news - for South Africa at least - but do we really understand what it is, what causes it and why it is good news for us here in the summer rainfall areas of South Africa?
El Niño and La Niña are the opposite phases of the two phase ENSO phenomenon. ENSO refers to the El Niño Southern Oscillation, the interaction between the atmosphere and ocean in the tropical Pacific that results in a somewhat periodic variation between below-normal (La Niña) and above-normal (El Niño) sea surface temperatures, as well as in dry and wet conditions over the course of a few years.
Spring has sprung - a flowering Scotia brachypetala or Boerboon tree.
Photo: Dr Peter Oberem
ENSO around for millennia
Many have asked the question: "Is ENSO part of global warming and caused by human activity, in particular our carbon emissions?"
Dr Peter Oberem, CEO of Afrivet clarifies, "Well, no, most scientists have high confidence that ENSO itself has been occurring for thousands of years, long before industrialisation and the increase in carbon emissions by ourselves, and will continue into the future.
El Niño and La Niña are naturally occurring climate patterns and humans have no direct ability to influence their onset, intensity, or duration. Global warming is, however, likely to affect the severity of impacts related to El Niño and La Niña, including extreme weather events."
Centuries before it was a focus of scientific study, South American fishermen noticed warmer-than-normal coastal Pacific Ocean waters and dramatic decreases in fish caught. This occurred periodically around Christmas time. They nicknamed the phenomenon “El Niño” (Spanish for little boy) in connection with the celebration of the Christian holiday marking the birth of Jesus.
In the 1980s, when the opposite phase of El Niño was discovered (i.e. cooler-than-normal ocean temperatures), scientists called it “La Niña” (Spanish for little girl).
El Niño warm; La Niña cool
According to Wikipedia, El Niño is the warm phase of ENSO and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including off the Pacific coast of South America.
The cool phase of ENSO is called La Niña with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific. The ENSO cycle, both El Niño and La Niña, causes global changes of both temperatures and rainfall.
Conditions in the equatorial Pacific Ocean prior to the occurrence of El Niño:
• The tropical pacific has consistent westerly moving trade winds. The trade winds push warm water on the surface of the ocean from east to west (westerly). This causes warm water to build upon the western side of the ocean near Asia.
• Meanwhile, on the eastern side of the ocean, near Central and South America, cold waters are pushed up towards the surface. Because of this, there is a difference in temperature across the equatorial pacific, with warm water to the west and cold water to the east.
• The warm water in the west heats the air, making the warm air rise and leading to drastic weather, including rain and thunderstorms. The rising warm air causes a circulation between east and west in the Pacific, with the warm, moist air rising in the west, and cool, dry air descending in the east.
• All of these natural occurrences lead to a reinforcement of the easterly winds and cause a self-perpetuating motion in the air in the Pacific.
This self-perpetuating motion in the air in the Pacific continues until the slow changes in the ocean around the equator lead to a series of events known as El Niño:
• Under the proper conditions, the trade winds are weakened, causing less warm surface water to be pushed to the west, and less cold water to be pulled to the surface in the east. Parts of the ocean that are cold during the usual self-perpetuating cycle become warmer, cancelling out the normal difference in temperature in the equatorial Pacific between east and west.
• With the ocean, temperature evened out, and the warmest waters being more toward the centre of the ocean, the cloudy, rainy weather that typically occurs in the east now occurs in the centre of the ocean.
• Rainfall patterns over the equatorial pacific are changed due to the diminishing of the trade winds and movement of warm water.
• This movement of the warm waters also causes a change in the wind cycles. The wind is now blowing out from the centre of the ocean to the east and to the west.
• All of this leads to drastic changes in temperature and weather around the world.
La Niña is a strengthening of the normal trade winds that typically occurs after El Niño. Basically, the normal, non-El Niño wind cycle is reinforced, pushing the warmest waters in the equatorial pacific further west than normal, and increasing the pulling up of cold water to the surface in the east.
La Niña has an effect on global weather, as well, and this effect is typically the opposite of El Niño, causing droughts in the eastern equatorial Pacific and east Africa (Kenya and Tanzania) and floods in the western equatorial pacific.
In southern Africa’s summer rainfall region, El Niño brings drought and La Niña brings rain, warmer minimum temperatures and warmer maximum temperatures (good agricultural conditions but also conditions under which parasites flourish.
As mentioned, Southern Africa can expect either a neutral/normal ENSO or a weak La Niña effect on our summer rainfall areas with rain and temperature conditions positive for agricultural production and for pasture growth.
At the same time, La Niña induced drought in many parts of the world, including Eastern Africa, will limit their production of grains such as maize wheat and rice, leading perhaps to shortages and good international prices for what we, with the favourable conditions, will be able to produce.
Feed, pastures, hay and grains should also be plentiful for us, promoting animal production. Parasites and parasite diseases, however, are also likely to benefit.
This means that we must be more vigilant (early detection and intervention is critical in ensuring the success of treatments) and vaccinate where possible to prevent outbreaks and to reduce their impact.
Diseases and parasite that come to mind are: rift valley fever, blue tongue, horse sickness, redwater (babesiosis), heartwater, gall sickness (anaplasmosis), ephemeral fever and lumpy skin disease, as well as ticks and worms (wire worm) in general.
Dr Peter emphasises: "Timeous vaccination, close observation, timeous detection, timeous treatment, are all essential during these times of plenty. Don’t be caught napping when vaccine supply runs low due to high demand. Do it now!"
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