Prepare for El Niño

Opinion editorial by Chris Brandolino, Principal Scientist - Forecasting, Earth Sciences New Zealand

 

Severe heat and drought overseas have understandably raised questions about what New Zealand’s spring and summer may bring.

At the same time, El Niño is tracking alongside, or ahead of, the strongest modern events.

For growers, the sensible response is neither complacency nor alarm, but early preparation for a wider range of plausible conditions.

New Zealand differs from Europe and Australia. Our maritime setting generally moderates temperature extremes, although short periods of exceptional heat remain possible, especially in eastern districts when hot air crosses the Tasman and descends on the lee side of mountain ranges. Growers should identify risks specific to each crop, block, region and growth stage.

El Niño is a naturally occurring shift in winds and warm water along the equatorial Pacific. When the usual easterly winds weaken or reverse, warm water moves eastwards. This redistribution of ocean heat changes tropical rainfall and influences the jet stream and weather patterns far from the equator, including around New Zealand.

It is not possible to provide a single deterministic forecast.

Current conditions strengthen confidence in the broad seasonal signal, but not in precise rainfall or temperature outcomes months ahead. Every El Niño has its own “personality”, so the following patterns are broad zones rather than property-level forecasts, and significant local variation should be expected.

In northern and eastern parts of both islands, the odds are tilted towards drier-than-usual conditions, particularly as spring progresses into November and summer. In the western North Island, dryness may occur at either end of the six-month period, with a potentially more normal rainfall window around December and early January.

Wetter-than-usual conditions are more likely in the western and southern South Island, increasing the risk of waterlogging, access disruption, disease pressure and localised flooding. In the South Island and lower North Island, south-westerly outbreaks may keep the risk of late frosts or cold snaps elevated deeper into spring.

Eastern districts may experience brief spikes of very hot weather when west to north-west winds develop. These warm, blustery periods can be followed within days by a front and a sharp south-westerly temperature change. Growers therefore need to prepare for volatility, not just seasonal averages.

Drought risk is more than a lack of rain. The most serious dryness is likely where below-normal rainfall, persistent wind and high temperatures coincide, accelerating evaporation and plant water loss. Even within a broadly dry season, isolated heavy-rain events remain possible and may damage crops or disrupt individual businesses.

There is no single horticultural impact. A dry summer may support flavour and sugar development in some fruit crops if adequate spring water has supported bud break and fruit set, while severely constraining shallow-rooted vegetables. Year-round vegetable production in areas more accustomed to flooding may be exposed if systems and crop plans are not designed for prolonged dryness.

Practical preparation starts with mapping exposure by crop, block and growth stage rather than relying on one seasonal assumption.

Growers can set operational triggers for changing irrigation frequency, protecting young plants, delaying planting, adjusting harvest timing or activating frost protection. Crop, place and timing will determine which actions matter most.

Growers should confirm water availability, including bore and well reliability, and check irrigation infrastructure before demand peaks. This will help identify constraints and address failures while parts and contractors are still available.

Growers can also review soil-moisture monitoring, mulching, groundcover, cultivation and drainage so soils can retain useful rain while safely shedding excess water.

It’s important to review insurance, business-continuity arrangements, labour plans and alternative supply options where weather disruption could affect harvest or market commitments. Plans should cover both water shortage and sudden excess, including drainage, erosion control, access, crop protection and recovery arrangements.

El Niño typically rises, peaks and weakens over many months. Current expectations are for the event to peak around November or December and then weaken, with effects potentially persisting through at least the following autumn.

Even as equatorial ocean temperatures return towards neutral, the atmosphere can retain momentum.

El Niño changes the odds -  it does not guarantee an outcome. It explains only part of New Zealand’s weather variability, with ocean temperatures, pressure systems and individual events also important.

A season may be drier than normal overall yet still contain a damaging downpour, frost, cold change or heat spike.

Growers should match their forecast tool to particular decisions. Long-range outlooks support seasonal planning, while shorter-range forecasts guide spraying, irrigation, frost protection and harvest. Use trusted meteorological advice and revisit forecasts frequently as a decision date approaches. Where possible, consider an ensemble of model outcomes: agreement increases confidence, while a wide spread signals uncertainty that should be built into decisions.

The best-prepared growers will plan beyond the first hot or dry spell. Water, crop, labour and financial decisions may need to cover a prolonged period of elevated variability. Early preparation, clear triggers and regularly updated forecasts will provide the strongest basis for protecting production and responding quickly as conditions develop.