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Abstract
Atmospheric rivers (ARs) are narrow and elongated regions of enhanced horizontal water vapour transport. Considerable research on understanding Northern Hemisphere ARs and their relationship with extreme precipitation has shown that ARs have a strong association with heavy rainfall and flooding. While there has been very little work on ARs in the Southern Hemisphere, global climatologies suggest that ARs are equally as common in both hemispheres. New Zealand in particular is located in a region of high AR frequency. This study aims to test the hypothesis that ARs play a significant role in heavy precipitation and flooding events in New Zealand. We used a recently developed AR identification method and daily station data across New Zealand to test for the concurrence of ARs and extreme rainfall. We found that, at each of the eleven stations analysed, at least seven to all ten of the top ten heaviest precipitation days between 1980 and 2018 were associated with AR conditions. Nine of the ten most damaging floods in New Zealand between 2007 and 2017 occurred during AR events. These results have important implications for understanding extreme rainfall in New Zealand, and ultimately for predicting some of the most hazardous events in the region. This work also highlights that more research on ARs in New Zealand is needed.
Highlights
New Zealand is located between 34 and 47oS, with a mountain range extending the length of the North and South Islands in the path of the prevailing midlatitude westerlies
Our results indicate a strong association between damaging New Zealand precipitation events and Atmospheric Rivers
About 60% of extreme rainfall events occurred between January and April, while August and September combined account for 3.5% of events
Summary
New Zealand is located between 34 and 47oS, with a mountain range extending the length of the North and South Islands in the path of the prevailing midlatitude westerlies. This research focuses on the hypothesis that atmospheric rivers play an important role in New Zealand’s rainfall and its extremes. An us Flooding from heavy rainfall is one of the many hazards faced by New Zealanders. Ericksen (1986) estimated that the nine most serious floods in New Zealand between 1968 and 1984 cost $NZ 353 million collectively The Insurance Council of New Zealand estimated that the 12 most expensive floods between 2007 and 2017 cost $NZ 472 million (ICNZ; Frame et al, 2020). Atmospheric rivers (ARs) are long, narrow regions of intense water vapour transport (Newell et al, 1992). Atmospheric rivers (ARs) are long, narrow regions of intense water vapour transport (Newell et al, 1992). Guan & Waliser's (2015) global climatology of ARs found a high frequency of landfalling ARs along coastal regions of Australia and New Zealand
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