The National Institute of Water and Atmosphere (NIWA) has confirmed that winter 2022 is the wettest and warmest on record for New Zealand. As I sat around in late November looking out at the seemingly endless rain, the words of the song “Have you ever seen the rain?” by Creedence Clearwater Revival kept running through my mind.
Why are we getting all this rain and when will it stop?
The cause of the high rainfall is a phenomenon called La Niña and during the last couple of years we are experiencing an example of a triple La Niña for the first time this century. It is important to understand that Aotearoa NZ is only one of many countries experiencing this exceptional phenomenon. Probably in terms of overall climate impacts this triple La Niña has been even more damaging to Australia than to Aotearoa NZ.
Why does it matter?
La Niña and its opposite, El Niño, are phases of a natural climate pattern across the Pacific Ocean that swings back and forth every few years. Together, they are called the El Niño-Southern Oscillation and make up the most dramatic year-to-year variation of Earth’s climate system. They can affect public health, freshwater availability, agriculture, wildlife, power generation and economic activity across the planet.
What causes La Niña and El Niño effects?
La Niña, like El Niño, is a weather pattern that originates in strong winds blowing warm water across the surface of the ocean from South America to Indonesia. It is an enhancement of the tropical Pacific climate in which stronger than normal trade winds blowing steadily towards the equator from the north-east in the northern hemisphere, or from the south-east in the southern hemisphere, push warm water toward the “maritime continent” to the north of Australia. The maritime continent is the large zone of ocean water located between the Indian and Pacific Oceans and encompassing Indonesia, Borneo, New Guinea, the Philippines, Malay Peninsula and the surrounding oceans. The warmer this maritime continent zone becomes, the more water evaporates around eastern Australia and Aotearoa NZ and this atmospheric moisture turns into rain.
How long will the rain and flooding continue?
With the Northland water table and streams already very full, further rain caused by the tail of La Niña, which is predicted to persist over December is likely to also cause more surface flooding.
To what extent does climate change and elevated greenhouse gases influence La Niña and El Niño events?
In 2021, an international team of scientists carried out a review of a range of different models to make predictions about the El Niño Southern Oscillation. They concluded that the variability of the El Niño Southern Oscillation is increasing in response to anthropogenic (man-made) greenhouse emissions. This means that the El Niño and La Niña fluctuations are getting more intense and becoming more frequent because of strengthening climate change and increased levels of greenhouse gases.
What future damaging effects will the triple La Niña have on weather patterns?
We know that severe, drought-inducing El Niño periods are always followed by intense or protracted La Niña periods. A final caution: NZ should be prepared for a continuation of this period of back-to-back severe seasonal climate patterns of extreme drought and extreme flood. After this exceptional triple La Niña, Northland should start preparing for a particularly severe drought in the not too distant future.