Why El Niño can bring drought, floods and unusual weather across the globe - IOL

Cabinet is preparing for the possible impact of an El Niño event in 2026-27, warning of pressure on water security, agriculture, drought preparedness and food supplies.

For the past weeks, South Africans have experienced scorchers, thunderstorms, heavy rain, winds and severe weather in a short span of time. 

This comes as reports of El Niño affecting parts of the world in different ways. 

The Pacific Ocean is warming at an unusually rapid rate. The current El Niño is already surpassing previous records and is expected to strengthen further before reaching its usual peak around December.

However, the effects of El Niño does not look the same for everyone. The climate pattern can have very different effects around the world. While some regions can experience drier conditions and an increased risk of fires, others can face heavier rainfall and flooding.

The reason lies in the relationship between the Pacific Ocean and the atmosphere above it.

Under normal conditions, trade winds over the tropical Pacific blow from east to west.

These winds push warm surface water towards the western Pacific, where it accumulates around Indonesia and surrounding areas.

As the warm water moves west, colder water from deeper in the ocean rises to the surface in the east. This process, known as upwelling, helps keep the eastern Pacific considerably cooler than the western Pacific.

The warmer western Pacific also plays an important role in rainfall.

Warm water encourages evaporation, which adds moisture to the air. The air above the warmer ocean also becomes less dense and rises. As it rises, it expands and cools, causing water vapour to condense into clouds and rain.

The resulting circulation forms part of what is known as the Walker circulation.

Air rises over the warmer western Pacific and spreads out higher in the atmosphere before some of it moves eastwards and sinks over the cooler eastern Pacific. Near the surface, air then moves back westwards as the trade winds.

This pattern helps explain why areas around Indonesia and the western Pacific generally receive substantial rainfall, while the eastern tropical Pacific and much of coastal Peru are considerably drier.

The ocean and atmosphere reinforce each other. Warm conditions in the western Pacific encourage rising air, while cooler conditions in the east encourage sinking air. The resulting circulation helps maintain the trade winds, which continue pushing warm water westwards and bringing colder water to the surface in the east.

Scientists refer to this reinforcing process as the Bjerknes feedback.

During El Niño, the normal pattern begins to change.

The trade winds weaken. This means less warm surface water is pushed towards the western Pacific and more warm water remains in the central and eastern Pacific, while the western Pacific can become relatively cooler.

The shift in warm water also changes where the strongest evaporation, rising air, cloud formation and rainfall occur.

As the warmer water moves eastwards, the area of strongest rainfall also shifts towards the central and eastern Pacific. This can result in wetter conditions in parts of the eastern Pacific and nearby areas, including coastal Peru.

The effects can be very different in the western Pacific.

With more air rising over the central and eastern Pacific, some air sinks over the western Pacific. Sinking air makes it more difficult for clouds to form, meaning areas such as Indonesia and the surrounding western Pacific can experience much drier conditions than normal.

These drier conditions can also increase the risk of forest and peatland fires in Indonesia.

The weakening of the trade winds further affects the Walker circulation. As the temperature difference between the western and eastern Pacific decreases, the pressure contrast that helps drive the trade winds also weakens.

The result is a Walker circulation that becomes weaker and shifts eastwards.

El Niño's influence is not only felt in the Pacific Ocean and its surroundings.

Changes in the location of rising air and rainfall can affect atmospheric conditions thousands of kilometres away.

These connections can influence weather patterns in distant parts of the world.

When water vapour condenses into clouds, heat is released into the atmosphere. During El Niño, the shift in the main zone of rising moist air and rainfall also changes where this atmospheric heating occurs.

This can warm the middle and upper tropical atmosphere beyond the Pacific.

In the Sahel, on the southern edge of the Sahara, this can make it more difficult for warm, moist air near the surface to continue rising. That can suppress rain-producing clouds and favour drier conditions.

Reduced cloud cover can also allow more sunlight to reach the ground, contributing to further warming and drying.

El Niño can also generate large atmospheric waves when the main area of rising air and rainfall shifts eastwards. These waves can travel far from the Pacific, affecting winds and storm tracks.

The effects can reach as far as Britain, where El Niño can increase the likelihood of wetter and stormier conditions during autumn and early winter, as well as increasing the risk of colder spells later in winter.

However, these links are less certain than some of El Niño's effects in the tropics because Britain's weather is influenced by several other atmospheric factors.

El Niño changes the odds of particular weather patterns, but it does not determine the weather in every location.

Its effects can also interact with conditions in other oceans.

For example, changes associated with El Niño can interact with the Indian Ocean Dipole, a difference in sea temperatures between the western and eastern Indian Ocean. This pattern has a strong influence on rainfall in East Africa and parts of India.

The result is that El Niño can create a broad tendency towards particular conditions while local weather systems still produce very different outcomes.

For example, Thailand generally tends towards drier conditions during El Niño. However, parts of the country, including Bangkok, experienced heavy rainfall and flooding in September.

India has shown a similar contrast, with the monsoon unusually dry overall while some areas still experienced intense rainfall and flooding.

The underlying lesson is that El Niño does not simply produce one type of weather across the globe.

Instead, a shift in the Pacific's warm water changes the circulation of the atmosphere. That shift can move rainfall towards some regions while suppressing it in others, and atmospheric connections can carry its influence much farther afield.

Local weather systems can still override these broader patterns, meaning a region that typically becomes drier during El Niño can still experience periods of intense rainfall and flooding.

We have established how the El Nino affects different parts of the world - and South Africa isn't the exception.

The National Disaster Management Centre (NDMC) said the country should focus on preparedness rather than wait for possible impacts to materialise, as the South African Weather Service (SAWS) forecasts indicate the current El Niño could become exceptionally strong by late 2026 or early 2027.

SAWS said its latest seasonal forecasts show an increase in probabilities of below-normal rainfall towards mid-summer, with “very high probabilities” of above-normal temperatures.

The weather authority stressed that Niño should not be regarded as a disaster, but it is vital for people to plan for it.