Two atmospheric rivers in the leadup to November 9 laid the foundation for the heavy rainfall that caused the Napier Flood. Photo / FileNew research points to New Zealand's costliest floods coinciding with "atmospheric rivers", but Niwa says November's flood in Napier was not directly triggered by the phenomena. Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that move huge columns of water vapour in the direction of preceding weather. Not all atmospheric rivers cause damage, but most - when hitting landfall - trigger a rain event of some sort. The research shows that Napier can expect its most frequent and impactful atmospheric river events from November to February.

Source: New Zealand Herald March 11, 2021 17:03 UTC