Fewer frost days as Central Otago climate alters

By Yvonne O'Hara

Projections suggest a reduction of about half the number of frost days. Photo / File
Projections suggest a reduction of about half the number of frost days. Photo / File

Southern Rural Life reporter Yvonne O'Hara continues her series of articles on climate change — part of a project developed with funding from the Aotearoa New Zealand Science Journalism Fund.

If changes in climate in Central Otago occur as projected, then many of the region's orchardists will be able to sleep through the spring nights.

Bodeker Scientific's report ''The past, present and future climate of Central Otago'' was researched and written by scientist Chris Cameron and other team members.

Projections using the maximum global warming scenario suggest a reduction of about half the number of frost days (up to 53 fewer) depending on location can be expected by the end of the century, and an average increase of 2degC over the same time.

Fewer frost days could in turn mean less need for frost protection and fewer nights of broken sleep for orchardists keeping on eye on their trees.

However, Ettrick orchardist Stephen Darling said while the report suggested there might be about half as many frost days projected through to the end of the century, he was more concerned about the pests and diseases that would enjoy the warmer climate as well as the effect it would have on fruit set.

Stephen Darling
Stephen Darling

Although Central Otago's winters at present are cold enough that winter chilling kills off the bugs and encourages stonefruit flowers to develop into fruit (fruit set), a few extra degrees in winter may affect that critical process.

''All fruit trees have varying threshold requirements to initiate fruit set,'' Mr Darling said.

''We need to understand the change and [level of] winter chilling that might be present in the future.''

He said the warmer conditions might lead to the selection and breeding of summer-fruit and pipfruit cultivars or new varieties that needed less chilling.

However, the biggest risk for horticulturists from the projected climate changes would be biosecurity incursions.

''We would have to be mindful of the risk of biosecurity pests, which will probably establish themselves here as there may likely be more favourable conditions than currently experienced in the region.

''We have, and will need, very rigorous biosecurity measures to prevent pests arriving or becoming established in the districts.

''Insect pests are our biggest risks and will not only have an adverse impact on our fruit and crops, there will immediately be restricted access to markets overseas and our products will not be permitted entry.''

The report indicated higher snow lines and less snow pack, which had implications for earlier snow melt into rivers and lakes and perhaps a change in quantity and flow.

''It is going to have a direct impact on hydro-electricity and [water] storage with a consequential effect on irrigation water supply because much of district's water supply indirectly comes from mountain catchments,'' he said.

In addition, harvest times may shift, especially if flowering times also shift and the growing seasons may be longer.

''However, if summer-fruit crops respond to the [predicted] hotter summer temperatures, we will see an enhanced summer-fruit industry.

''That will also mean increasing sugar levels in fruit, and that enhances its eating quality, which is a desirable attribute in the market.''

- Otago Daily Times

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