The impact of El Niño and La Niña on New Zealand's climate
Although El Niño and La Niña (collectively known as El Niño-Southern Oscillation or ENSO) have an important influence on New Zealand’s climate, it accounts for less than 25 percent of the year-to year variance in seasonal rainfall and temperature at most locations. Nevertheless, its effects can be significant.
Typical El Niño impacts on New Zealand's climate
New Zealand typically experiences stronger or more frequent winds from the west in summer, leading to an elevated risk of drier-than-normal conditions in east coast areas and more rain than normal in the west—due to the barrier effect of the Southern Alps and main North Island ranges.
In winter, colder southerly winds tend to prevail, while in spring and autumn, southwesterlies tend to be stronger or more frequent, bringing a mix of the summer and winter effects.
During particularly strong El Niño phases, these effects can be more intense.
The impacts of the 2015/16 El Niño
In 2015/16, we experienced a very strong El Niño. NIWA climate scientists used past strong El Niño events to approximate what may happen during the summer of 2015/16.
In the El Niño events of 1972/73, 1982/83 and 1997/98, severe drought occurred in eastern parts of the country. While a typical strong El Niño pattern of south-westerly winds occurred in December of 2015, a change to more northerly-quarter winds than usual for January and February brought more rain and alleviated fears of El Niño-associated drought in many parts of the country.
While east coast drought is not a certainty during every El Niño as 2015/16 demonstrated, the risk of El Niño-driven drought during a strong event is enough to warrant risk-management actions by farmers and others whose livelihoods are likely to be adversely affected by prolonged dry conditions.
La Niña’s impacts on New Zealand
La Niña events have different impacts on New Zealand's climate. More north–easterly winds are characteristic, which tend to bring moist, rainy conditions to the north–east of the North Island, and reduced rainfall to the south and south–west of the South Island.
Therefore, some areas, such as central Otago and South Canterbury, can experience drought in both El Niño and La Niña. Warmer than normal temperatures typically occur over much of the country during La Niña, although there are regional and seasonal exceptions.
Keeping track of ENSO with NIWA
NIWA produces a range of publications about the climate of New Zealand, including the strength and likely impact of El Niño, La Niña, or the likelihood of ENSO-neutral conditions.
Two key publications are our Seasonal Climate Outlook and Hotspot Watch.
Seasonal Climate Outlook
NIWA's Seasonal Climate Outlook provides air temperature, rainfall, soil moisture and river flow predictions for the coming season. The latest Outlook discusses the likely impacts of this year's El Niño.
This weekly update helps assess likelihood of extremely dry weather preceding a drought. Regions experiencing severely to extremely drier than normal soil conditions are deemed “hotspots”.