Domestic wine production's set to fall to its lowest total in two decades

A forecast 21 percent decline in New Zealand this year, has contributed to a Southern Hemisphere slump, after extreme weather affected harvests.

Director-general of International Organisation of Vine and Wine, John Barker says wine production is always up and down.

He says it used to be worse, before there was better technique.

Barker says the variation between global harvests have grown in the last 15 years, due to climate change.