Meteorologist Vivien Whyte talks to celebrated climate scientist Dr Jim Salinger about the upcoming El Niño, which many scientists around the world are predicting will be the strongest in decades.

Deep in the throes of winter, I can’t help but dream of the summer ahead. Days spent at the beach, a break from the tempestuous winds of Wellington and a chance to enjoy my favourite outdoor activity, tramping, in the longer daylight hours. It seems, however, that I’ve been dreaming of summer since last summer! Which stayed wet, dreary and cold for far longer than I would’ve liked. In fact, many will remember the summer for its weather headlines of floods, slips and cyclone warnings.

Looking towards this summer, the weather is looking to flip the script. Places that were flood-ridden and wet are looking to be scorching hot and dry. And places that were dry and sunny are looking to be wet and windy.

But what’s going on?

Well, our weather is determined by a complicated mix of day-to-day weather patterns, local effects, yearly to decadal climate oscillations, and many more things – all lying now on the foundation of a warming climate. The big player here that’s going to control our summer weather so dramatically is an upcoming flip from La Niña to El Niño. An El Niño that many scientists around the world are predicting will be the strongest in decades.

While weather refers to the wind, rain or sun you experience on the day-to-day, climate refers to your average weather over the long-term. For example, the weather on a particular summer day in Tāmaki Makaurau might be cloudy and windy, but the summer climate there is usually sunny, warm and subtropical. And although Auckland weather may change dramatically day to day, the climate is steadily becoming warmer and increasingly humid. Although a changing climate affects our local weather patterns, what actually happens is a lot more complicated than a linear line of temperatures going up, up and up.

Our local weather is also affected by global climate patterns: oscillations of warm and cold phases that have been going on for hundreds if not thousands of years. The most prominent of which for Aotearoa New Zealand include La Niña and El Niño (ENSO: the El Niño Southern Oscillation), Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM). Each of these brings out a different colour to our weather. Not only that, but they interact to form a unique colour palette for each season. Like different sized cogs in a clock, these three oscillations work on time frames from weekly (SAM) to a handful of years (ENSO) to decades (IPO).

What’s causing the extreme weather?

Having said that, the flip in New Zealand’s summer weather this year will primarily be caused by the El Niño Southern Oscillation. The summer just past famously came 5 months too late. With sunny, rainless days only gracing the country in May… just in time for a chilly plunge into winter. Underpinning this humid, wet summer was a distinct La Niña flavour, which is characterised by higher rainfall in the northeast of the mōtū, heightened tropical cyclone risk, and less rainfall for western and southern regions. In fact, the last time La Niña was seen was in 2021-22, which was the same summer that saw the Auckland Floods and Cyclone Gabrielle. Looking towards this year’s summer, scientists have confirmed that we will be see-sawing over into the yin to La Niña’s yang: El Niño.

El Niño and La Niña represent opposite phases of the Pacific Ocean’s year-to-year personality. Dr Salinger points out that “El Niños have always occurred back in time.” In fact, “they were first named by people off the coast of Peru when they got unusually warm water around December.” The name El Niño means “The Christs’ Child” and was given when Peruvian fishermen noticed that every 3-7 years there would be less anchovies to fish. This is because during an El Niño event, water off the coast of Peru is warmer than usual, less phytoplankton survive and thus fewer anchovies can feed and survive to adulthood.

Having a warmer than usual eastern Pacific Ocean is one of the key indicators scientists look out for when declaring an El Niño event.

And while that means less anchovies on the coast of Peru, Dr Salinger describes the flow on effects for us in Aotearoa as hot and dry weather for the east of the North Island, but wet and temperate conditions for the south and west of the motu.

“So the areas, certainly, which are most sensitive to El Niño are the hot and dry ones, like Gisborne and the Hawkes Bay, and the wet ones on the south west of the South Island.” he says.

What are the potential impacts?

The upcoming El Niño is just warming up – literally – and will be in full play by spring. We’re expecting a complete opposite flip from the summer just past. For example, while those in Gisborne and Hawkes Bay may brace for cyclone risks during La Niña years, the opposite holds true during an El Niño, which promises hot and dry weather. Dr Salinger says “I imagine that in this case it’ll be a hot El Niño. In other words, we might see record temperatures in the east of the North Island.” Dr Salinger says that “those in the areas that are likely to be drier should want to drought proof their activities”. At the same time, the risk of flooding will increase for Southland and the west coast.

A big part of the El Niño story is that wind flow and direction will change. Commenting on the flip from La Niña, Dr Salinger says

“the story is that it’ll be very windy – no doubt about that.”

Like many Wellingtonians, I have come to appreciate the difference between cold southerly winds whipping up from Antarctica, and more temperature northerlies cruising down from the tropics or Tasman Sea. But even subtler changes in wind direction have a strong effect on rainfall and temperature. Dr Salinger notes that “once you get into spring or summer, certainly summer, you get the westerlies blowing – which is what happens in an El Niño. Spring has a southwesterly flow, and then the airflow tilts west in summer. That’s when I’d expect to see some very high temperatures in the east of the North Island.” It’s these winds, blowing in from Australia, that will help give the upcoming El Niño its distinctly hot flavour in the north and increase rainfall in the south-west.

Naturally, some El Niño events are stronger than others – and this one is predicted to be one of the strongest on record. Dr Salinger describes El Niño as the underlying flavour of the upcoming seasons. “Of course, anything will happen… I always used to say that each season has its own personality. So we can anticipate the personality but not what happens.” Dr Salinger cites previous strong El Niño events as examples of the colour of this personality. For example, “a classic case was 1979, when Queenstown had double its average rainfall and Napier had half. That was a big El Niño.”

How can we prepare?

With all this in mind, New Zealanders are being warned to prepare for the upcoming summer:

For the north and east this means preparing for dry conditions, drought and elevated wildfire risks. For the west and south this means preparing for increased rainfall and westerly winds bringing a heightened risk of flooding and erosion. Generally, being proactive and planning for the risks is going to be key. Whether that be clearing storm drains, managing vegetation or saving up water. An example he gives is:

“if you were in the east of the North Island and if you were a farmer, you’d have to manage livestock and feed. So if they’re putting down more feed because it’s going to be dry, that’s a good insurance policy”.

Thinking about my summer coming up, I’m thinking about tramping in gusty winds and ensuring I know how to be outside in potentially wilder or dryer weather depending on where I am. An important part of this is staying on top of the weather forecast because hikes, beaches and places I think I know well won’t be playing by their usual rules.

But that’s just talking about the summer coming up. The back and forth between El Niño and La Niña years has been happening for centuries. However, these swings are now happening in the context of a warming climate. Shifting high temperatures higher, making rainfall extremes bigger and giving us an El Niño year that might feel too hot to handle. As Dr Salinger says “the warming climate has certainly shifted the baseline”, citing the 1997/98 El Niño event as an example of this shifting baseline. “When we came to having an El Niño in 97/98 it was (what I’d call) a “hot” El Niño – no area was cold in that sense.”