Explainer: Why all this flooding in the North Island? The landscape of both islands is characterised by high elevation spines running along the length of the South Island and a large part of the North Island. The North Island has four climate zones; the South Island also has four. In this case, Cyclone Debbie decayed as it passed over the Tasman and tracked across the North Island and upper South Island. Niwa's March climate summary says significant rainfall was experienced across the upper North Island, with most locations in the entire North Island experiencing normal or above-normal rainfall.

Source: Stuff April 05, 2017 04:56 UTC