The Pacific Ocean is changing again, and for Australia, New Zealand and their neighbours, the consequences of El Niño can be dramatically different depending on which side of the Tasman — or which part of the Pacific — you call home.

At the same time that parts of Asia experience extraordinary rainfall and tropical weather, El Niño can increase the likelihood of dry conditions elsewhere.

That apparent contradiction demonstrates why El Niño is frequently misunderstood.

It is not simply a wet-weather or dry-weather phenomenon.

It is a reorganisation of one of the world's great climate systems.

What is El Niño?

El Niño is the warm phase of the El Niño–Southern Oscillation.

During an El Niño event, trade winds across the tropical Pacific weaken and unusually warm surface water becomes established farther east.

The atmospheric circulation above the Pacific changes with it.

Rainfall patterns move.

Winds change.

Storm behaviour can change.

And those changes can influence weather thousands of kilometres from the equator.

Few regions are more exposed to those changes than Australasia.

Australia generally becomes drier

For Australia, the classic El Niño signal is an increased likelihood of below-average rainfall across parts of eastern and northern Australia, particularly during winter and spring.

Warmer daytime temperatures are also more likely across much of the country.

That combination can reduce soil moisture, affect agricultural production and increase bushfire risk.

Northern Australia's wet season can also begin later during El Niño years.

Australia generally experiences fewer tropical cyclones during El Niño events, although individual severe cyclones remain possible.

New Zealand is different

Cross the Tasman and the story changes.

New Zealand's El Niño climate is strongly influenced by changes in prevailing winds.

El Niño conditions tend to produce more frequent or stronger westerly and southwesterly winds over New Zealand.

That can create very different conditions on opposite sides of the country's mountain ranges.

Western areas can become wetter.

Eastern regions can become drier.

Temperatures can also be affected by increased southerly airflow.

Consequently, an El Niño forecast that means increased dryness for eastern Australia cannot simply be applied to New Zealand.

Geography matters.

Agriculture on both sides of the Tasman

Australia and New Zealand are both major agricultural exporters, but El Niño can challenge them differently.

Australian grain and livestock producers may become increasingly concerned about rainfall deficits and pasture availability.

New Zealand farmers may face strong regional differences, with western and eastern districts experiencing very different conditions.

Dairy, sheep, beef, horticulture and cropping operations therefore need to interpret El Niño through local conditions rather than regional headlines.

And then there is the wider Pacific

For Pacific Island nations, ENSO is enormously important.

Rainfall can shift significantly between island groups.

Some areas can become unusually dry while others experience increased rainfall.

Changes in tropical cyclone behaviour are also important.

During El Niño, tropical cyclone activity can shift eastwards across the South Pacific.

That can alter the geographical distribution of cyclone risk.

For small island economies, the consequences can be profound.

Water security, agriculture, tourism and infrastructure can all be affected.

The Philippines demonstrates the complexity

Recent heavy rainfall and tropical weather affecting the Philippines and surrounding parts of Asia provide a useful reminder that El Niño should never be interpreted as meaning that the entire western Pacific becomes uniformly dry.

Monsoons continue.

Tropical cyclones continue.

Individual weather systems can still produce exceptional rainfall.

El Niño changes the background climate and the probability of particular conditions.

It does not control every individual weather event.

Weather becomes trade

Australia and New Zealand are deeply integrated into Asia-Pacific supply chains.

Agricultural production, shipping, tourism and energy consumption can all be influenced by seasonal weather.

Poor Australian grain production can affect export volumes.

Changes in New Zealand dairy conditions can influence production.

Severe weather in Asian manufacturing centres can disrupt supply chains.

Cyclones can damage Pacific tourism infrastructure.

What begins as a change in ocean temperature can ultimately become a commercial event.

Food prices can transmit the effect

Australasia is a major food-producing region.

Weather therefore influences not only domestic food availability but international commodity markets.

Reduced production in one country can sometimes be offset by increased production elsewhere.

But widespread climate disruptions can push prices higher.

Consumers eventually experience those changes at supermarkets and restaurants.

A Pacific phenomenon requires a Pacific perspective

Perhaps the greatest mistake when discussing El Niño is looking at one location and attempting to extrapolate its weather across the region.

The Pacific is enormous.

Australia can be dry while another country floods.

Western New Zealand can experience substantial rainfall while eastern districts dry.

One Pacific island group can struggle with water shortages while another faces damaging tropical weather.

All can be experiencing consequences of the same broader climate system.

What happens next matters

The strength and duration of the developing El Niño will be important.

So will other climate influences.

For Australia, spring rainfall will be watched particularly closely.

For New Zealand, wind patterns and regional rainfall distribution will matter.

Across the Pacific islands, rainfall and cyclone patterns will become increasingly important as the Southern Hemisphere moves towards summer.

No single forecast can adequately describe the consequences for the entire region.

The Australasian View

El Niño demonstrates something Australians and New Zealanders sometimes forget.

We live beside the same ocean, but we do not necessarily experience the same weather.

A changing Pacific can dry eastern Australia, alter winds and rainfall across New Zealand and shift rainfall and cyclone risks throughout the Pacific islands.

That makes El Niño more than an Australian weather story.

It is an Australasian economic, agricultural and environmental story.

The Pacific connects our region.

El Niño reminds us just how powerful that connection can be.