Rethinking extreme heat in a cool climate: A New Zealand case study

Abstract

New Zealand is one of many higher latitude countries where extreme heat is perceived to be a less consequential impact of climate change, by virtue of its relatively cool climate. Consequently, metrics to quantify the impacts of extreme heat in New Zealand have not kept pace with wider improvements in heatwave definitions. This study evaluates different methods to quantify extreme heat in New Zealand, with a view to improve the knowledge base underpinning future climate change risk assessments. Specifically, this analysis (1) reveals which of New Zealand's purportedly hottest years in the satellite era are robust to different definitions of extreme heat; (2) introduces a new method of quantifying extreme heat which is applicable across different regions, and serves equally well whether an analysis is contextualised relative to the past (attribution) or for the future (projections); (3) detects previously unidentified heatwaves over recent decades; (4) identifies locally significant increases in extreme heat and the potential lengthening of summer months after only 0.5 ◦C of global warming; and (5) discusses further research priorities to better understand the impacts of extreme heat in New Zealand over the coming decades.