How does ENSO typically affect New Zealand?
During El Niño, New Zealand tends to experience stronger or more frequent winds from the west in summer, typically leading to drought in east coast areas and more rain in the west. In winter, the winds tend to be more from the south, bringing colder conditions to both the land and the surrounding ocean. In spring and autumn south-westerly winds are more common.
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.
Although ENSO events have an important influence on New Zealand's climate, it accounts for less than 25% of the year to year variance in seasonal rainfall and temperature at most New Zealand measurement sites. East coast droughts may be common during El Niño events, but they can also happen in non-El Niño years (for example, the severe 1988–89 drought). Also, serious east coast droughts do not occur in every El Niño. However, the probabilities of the climate variations discussed above happening in association with ENSO events are sufficient to warrant management actions and planning to be taken when an El Niño or La Niña is expected or in progress.