Otago Daily Times

‘Atmospheri­c river’ research explains extreme rainfall events

- JOHN LEWIS john.lewis@odt.co.nz

‘‘ATMOSPHERI­C rivers’’ which bring weather bombs to New Zealand are expected to increase in frequency and magnitude, and move further south in coming years, new research from the University of Otago shows.

Atmospheri­c rivers are narrow corridors of concentrat­ed moisture in the atmosphere, and are the cause of major storms like the one that hit the South Island on March 25, 2019.

University of Otago masters of science graduate, 2020 New Zealand Fulbright Scholar and research lead author Hamish Prince said the storm produced the highest total of rainfall (1086mm) over a 48hour period in New Zealand recorded history.

It killed one person, washed away the Waiho Bridge near Franz Josef, caused millions of dollars’ damage, and a state of emergency was declared.

“This flood was produced by one of the most extreme atmospheri­c rivers observed over New Zealand, moving incredible amounts of moisture very quickly through the atmosphere, extending over 4000km and covering much of the South Island of New Zealand.

‘‘Understand­ing the climatic processes controllin­g atmospheri­c rivers, and how to predict them at weekly, seasonal, and annual timeframes can help mitigate damages and loss from such impactful events.’’

He said about 40 atmospheri­c rivers made landfall in New Zealand each year.

The most impactful atmospheri­c rivers occurred about once every five years, but evidence suggested these events could become more frequent and more intense in a warming climate.

‘‘In very basic terms, one of the results of a warmer climate is a wetter atmosphere.

‘‘With more moisture in the atmosphere, the frequency and magnitude of atmospheri­c rivers making landfall in New

Zealand are expected to increase,’’ he said.

‘‘The increase in extreme precipitat­ion is not expected to occur equally throughout the nation however, with indication­s that the landfallin­g location of atmospheri­c rivers is shifting southward in New Zealand,’’ Mr Prince observed.

He also said the benchmark study would allow atmospheri­c rivers to be monitored to identify shifts in their behaviour as weather continued to be influenced by climate change.

‘‘Our study has shown that atmospheri­c rivers are responsibl­e for the vast majority of extreme rainfall in New Zealand — along with over 50% of all precipitat­ion — so understand­ing what drives these events is fundamenta­l to planning for extreme weather and the management of freshwater resources in New Zealand.’’

Mr Prince now works at the University of California, San Diego, Scripps Institutio­n of Oceanograp­hy Centre for Western Weather and Water Extremes, where he continues to examine the predictabi­lity and economic impact of atmospheri­c rivers.

 ?? PHOTO: SUPPLIED ?? Eyes on the skies . . . University of Otago masters graduate and 2020 New Zealand Fulbright Scholar Hamish Prince has recently published new research on atmospheri­c rivers in New Zealand.
PHOTO: SUPPLIED Eyes on the skies . . . University of Otago masters graduate and 2020 New Zealand Fulbright Scholar Hamish Prince has recently published new research on atmospheri­c rivers in New Zealand.
 ?? PHOTO: WAYNE COSTELLO ?? Washed out . . . The State Highway 6 bridge over the Waiho River is ripped apart after an ‘‘atmospheri­c river’’ made landfall on the West Coast on March 25, 2019.
PHOTO: WAYNE COSTELLO Washed out . . . The State Highway 6 bridge over the Waiho River is ripped apart after an ‘‘atmospheri­c river’’ made landfall on the West Coast on March 25, 2019.

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