A new study has revealed the effect that El Niño and La Niña are likely to have on the New Zealand climate in the coming decades with a continuation in the global climate change.
“As the world continues to warm New Zealand is likely to experience the impacts of El Niño and La Niño events with comparable intensity and frequency to what we have seen over the last three decades, and possibly more so,” says lead researcher Dr Anthony Fowler from the University of Auckland School of Environment. “This means that we should anticipate more extreme events, such as flooding and droughts, in the regions affected by these weather patterns.”
The study was published in the journal Nature Climate Change and is the result of a climate record compiled from reading kauri tree rings which allowed the researchers to see back to approximately AD 1300.
The El Niño and La Niña climate patterns affect different areas of our planet differently.
“The El Niño / La Niña phenomenon has been referred to as the heartbeat of the world,” Dr Fowler says. “After the seasonal cycle and monsoons, it’s the most important source of year-on-year climate variation. Strong events often cause incredible damage and affect hundreds of millions of people around the world. El Niños, in particular, have been responsible for some of the devastating 20th century droughts in Australian, floods in South America, and failure of the monsoons in India.”
Conversely, La Niña is at the core of the massive flooding in the north-east of Australia over the past several years and other intense precipitation events around the region.
For New Zealand, El Niño is normally the bringer of cooler south-westerly winds, an overall cooling and droughts in sheltered eastern areas of both the North and South island.
La Niña, naturally, reverses this trend, bringing moisture laden air from the sub-tropics which conversely elevate the temperatures, especially in the North Island. With La Niña also comes higher precipitation which, in some cases, leads to flooding.
“To date the global climate models used to ’predict’ the future have been unable to give us a clear picture of what will happen with El Niño and La Niña as the world warms,” says Dr Fowler. “But understanding the phenomenon is critical to learning what climate change will mean for the world’s population.”
“The premise of our work is that we know that the world has warmed over the last few centuries and we can look back to see what has happened with El Niño / La Niña over that time. By studying how the phenomenon has behaved in the past we can anticipate what might plausibly happen in the future. This should result in more informed scenarios of future regional climate change.”
Regarding the kauri tree rings, Fowler explained that “Kauri trees are quite sensitive to these weather patterns. During El Niño events they grow rapidly and have wide tree rings whereas during La Niña events they grow more slowly and have narrow rings.”
“Notably wide and narrow kauri tree rings have become more frequent as the world has warmed over the last few centuries. We infer from this that El Niño and La Niña events become more frequent or intense as the world warms, or that New Zealand’s climate becomes more strongly influenced by such events. Either possibility suggests that droughts and floods related to El Niños and La Niñas will continue to significantly affect New Zealand, and may well become more intense.”
Dr Fowler says that stitching data together from living trees and logged wood, to create a continuous record of the last 700 years, was a significant achievement for the research team. He notes the irony in one form of environmental damage yielding clues about another. “Kauri logging in the 19th and early 20th century devastated the landscape,” he says. “But a lot of the wood that was cut down can still be found in the weatherboards of our houses and provided important data for our research.”