Warming puts squeeze on grape harvest
Grape expectations Wine makers will have to change the way they manage their vineyards to deal with climate change, according to a new report.
This latest study has found grape ripening is getting earlier in many of Australia's premier wine regions due to rising temperatures and drying soils.
Vine management practices such as decreasing the crop yield are also contributing to early ripening, they say.
According to previous research, grapes have been ripening earlier across southern Australia by around eight days per decade over the last 25 years.
To understand this shift, Dr Leanne Webb from CSIRO and her team have now analysed decades of records from wine-growing regions across southern Australia.
"This has been a study of potential influences on wine-grape maturity trends on a continental scale," says Webb.
The team studied 10 vineyards growing different species of grapes in five major wine-growing areas in Victoria, South Australia and Western Australia.
Their results are published today in the online edition of Nature Climate Change .
The researchers say the study will help wineries develop strategies to deal with climate change.
"If you can work out what is causing it, then you can see whether there's any buttons or levers you can actually use to make changes if it gets hotter," says study co-author Professor Snow Barlow from the University of Melbourne.
He says most winemakers don't want the fruit to ripen early as this is usually when the weather is hotter.
"Hot vintages are not good for quality wines," says Barlow.
The researchers found that early ripening was due to a shift towards a warmer climate, which spurs sugar production, and drier soils, which activate stress hormones in the roots that promote maturation.
Practices such as reducing crop yields - pruning of vines so that more energy goes into producing a smaller number of grapes - also contributes to early ripening.
"It does appear that changes in climate, particularly changes in soil moisture have been driving the grapes towards maturation, and it would appear that some management interventions that have some effect on yield may also have been taking the grapes in that direction," says study co-author Dr Penny Whetton from the CSIRO.
The researchers used the records of sugar levels kept by the vineyards covering the period 1985 to 2009 to assess how grape maturation times had altered over time.
Winners and losers
They combined this with temperature data from the Bureau of Meteorology, modelling of soil moisture and records of crop yields from the winegrowers.
They found that early grape maturation had occurred in all the vineyards except Margaret River in Western Australia, which had actually dropped back by about half a day per decade.
"When we first did this work it worried us enormously," says Barlow. "But when we actually looked at the temperature records of Margaret River, it hadn't warmed."
"So there are regional differences in the degree of warming that has occurred."
While the Margaret River winery did well, Barlow says the biggest shift was seen in the Mornington Peninsula, where some species of grape had ripened around 15 days earlier per decade.
"Traditionally because it's wetter [in the Mornington Peninsula] they hadn't really had to worry about [crop irrigation], but if you look in the last 15 years it hasn't been as wet," says Barlow.
While there's not much that winegrowers can do about changing climate, the researchers say the study suggests that changes in irrigation practices, soil management and crop yield practices might save them from having to take more radical action such as change styles, varieties or even relocate.
"Soil moisture and the yield are both areas where the grape growers can have some control," says Whetton. "Through this research they can give themselves a bit more control over when the grapes mature."
She says the study also has broader implications for understanding the effects of climate change.
"There isn't a lot of work in the southern hemisphere relating trends in biological systems to changes in climate, so this work is actually quite interesting in more generally demonstrating that connection."