Most intense heatwave of century behind early harvest

The hottest January in New Zealand’s recorded history caused the country’s largest wine region to have its earliest ever grape harvest, a new study shows.

The summer of 2017/18 was the most intense heatwave of the past century, with air and sea temperatures in New Zealand averaging about 2 degrees Celsius above normal.

According to research by Dr Jim Salinger, the heat caused early flowering and ripening in Marlborough grapes, resulting in a harvest about two weeks ahead of normal to make sure desired sugar levels were achieved.

‘‘In January [2018] there were huge anti-cyclones that calmed the Tasman Sea down . . . that month was about 3 degrees above average. It was the warmest month ever,’’ Salinger said.

The high temperatures sped up the fruit cycle and pushed crops towards early maturity.

Salinger and a team of researchers explored the effects of the three most intense ocean atmosphere heat-waves of the century, which took place in 1934/35, 2017/18 and 2018/19.

‘‘We wanted to see what caused them, the impacts they had, and the relationships with global warming or anthropogenic climate change,’’ Salinger said.

He presented the findings at the Marlborough Research Centre last week, explaining how the heatwaves had affected agriculture, glaciers, and marine ecosystems.

Marlborough-based Plant and Food scientist Dr Mike Trought said as conditions warmed, flowering and harvest would occur earlier.

Harvesting at warmer times of the year changed the balance of sugars and acids in the fruit, which resulted in a different style of wine. He thought Marlborough, famed for its sauvignon blanc, could end up being more suitable for merlot. North Canterbury could become sauvignon blanc country.

There were potentially management techniques, like increasing yield, which could delay the onset of early ripening, he said.

The average vineyard lasted about three decades, Trought said. ‘‘That means people making decisions planting now, are going to have to live with those decisions for 30 years or more, under conditions of climate change.

‘‘Understanding or potentially anticipating how these changes in the climate . . . are going to impact on our industry in the medium to long term is really important.’’

Salinger and his team also revealed the 2017/18 heatwave caused the largest loss of glacier ice in the Southern Alps since 1962. It caused ‘‘dramatic losses’’ of bull kelp, and a complete loss of a southern kelp species at Pile Bay near Christchurch, where sea surface temperatures exceeded 23C.

New Zealand King Salmon lost 1600 tonnes of fish in 2018, many of which overheated in warmer than usual Marlborough Sounds farms.