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New Zealand faces decades of drought, flooding, intense winds and enormous changes to farming and crop production because of global warming, a new book on the future of our weather reveals.
Kiwifruit growing will be squeezed out of some regions, wine will be grown in Southland, olives in Dunedin and average temperatures will rise up to 4C under scenarios painted by science writer Gareth Renowden in Hot Topic: Global Warming and the Future of New Zealand (AUT Media), published next week.
Renowden has drawn on Niwa studies and international research to pinpoint what global warming will mean for New Zealand over the next century, pointing to heatwaves and regional droughts in the north and east of the country, while the west and south faced intense rain and flooding.
Renowden, an olive, grape and truffle grower in Canterbury, says New Zealand - like the rest of the world - can expect average temperatures to rise between 2C and 4C by the 2090s.
"Heatwaves will become more frequent and we can expect fewer frosts," he writes. "That can already be seen - the number of cold nights and frosts per year has diminished by 10-20 since 1950."
Renowden says that by the end of the century, Taranaki, Manawatu, the West Coast, Otago and Southland will have higher average rainfall, while Hawke's Bay, Gisborne and the eastern parts of Canterbury and Marlborough will be drier. "Large rainfall events are expected to become up to four times more common by the end of the century... rainfall will generally become more intense."
Over the whole of the country, there could be 20 per cent more rain on the three wettest days of the year, he says. On the West Coast that will mean 40mm more rain on each of those days. Canterbury will get 50 per cent more rain in the year's heaviest falls.
Renowden says droughts will also increase; the frequency of a one-in-20-year drought might double by the 2080s in inland and northern Otago, parts of Canterbury and Marlborough and in Wairarapa, Bay of Plenty and Northland. And that is under a "low-to-medium" warming scenario. That same one-in-20-year drought would be four times more likely in many areas under a medium-to-high warming scenario. This will mean demand for irrigation will increase considerably and warmer and shorter winters will mean a higher snowline.
Niwa's latest studies suggest that by the end of the century, Mt Cook could have an average summer temperature increase of 6C (from 14-20C) which would have a major impact on snow levels and could cause large rockfalls and landslides.
Rising sea levels are of most concern in our island nation and Renowden says Niwa is warning of a 20cm rise in sea level by 2050, and a 50cm rise by 2100.
"However, sea-level rise and in particular the rate of melting of the Greenland and West Antarctic ice sheets are the areas of greatest uncertainty at the moment, so those numbers may have to be revised upwards."
All these changes would have a profound effect on our flora and fauna: Renowden points to the decline in kiwifruit production - which requires winter chilling - around Kerikeri since the early 1990s and says the production of the main kiwifruit cultivar, Hayward, could become uneconomic in the Bay of Plenty after 2050.
But he says New Zealand will be better off than most of the rest of the world thanks to the oceans around us slowing the rate of warming.
"The sea will be our air-conditioner, keeping us cool - at least in comparison with the rest of the planet."
Also in New Zealand's favour is our small population and large land area, which could help us live sustainably within our own borders. But, he warns: "Learning to live with and trying to limit climate change is going to drive national and international politics over the next century."
