In two recent research papers scientists at the University of Melbourne and CSIRO have identified the advance in the early ripening of wine grapes and attributed this advance to climate warming and declines in soil water content.

The study reveals that management factors have also influenced the shift, offering hope for growers to develop adaptation strategies.

The studies, led by climate scientist and viticulturist Dr Leanne Webb, were published in the journals Global Change Biology (April 2011) and Nature Climate Change (February, 2012) and conducted by scientists from CSIRO and the University of Melbourne.

In the Global Change Biology study, scientists made an extensive assessment of harvest diaries from vineyards in southern Australia to determine the presence of historical trends in winegrape maturity dates.

The 44 vineyard sites studied are located in geographically and climatically diverse winegrape growing regions across four states in Australia. 

In contrast to previous studies that use harvest dates to indicate grape maturity, the research team examined berry-sugar concentration records to detect the trends to earlier wine-grape ripening.

For the period 1993–2009, 43 of 44 vineyard blocks displayed trend to earlier maturity. For 35 of these sites the trend was statistically significant. Only one Margaret River vineyard in Western Australia ripened later.

In 10 of these 44 vineyard sites longer records of observations, periods of up to 64 years (41 years on average), had been kept.

For these sites, the study revealed an increase in the rate of advance of maturity over more recent decades.

Over the more recent 1993–2009 period, the average advance was 1.7 days year, whereas for the period 1985–2009 the rate of advance was 0.8 days yr_1 on average.

Determining the underlying causes of these shifts was the next step, especially with earlier maturing potentially impacting wine-grape quality and regional branding. 

This study, published in Nature Climate Change, set about to test the assumption that earlier ripening of winegrapes was due to observed regional warming.

What was found was that at these 10 vineyard sites only about a third of the shift was driven by regional warming.

Other factors were also affecting the timing of winegrape ripening. On average, over the period 1985-2009, early ripening of Australian wine grapes are equally attributable to climate warming, declines in soil water content, and lower crop yields.

An additional influence from changing management practices is also likely.

Human-induced climate change is a driver of this grape response, given that previous studies have linked Australian temperature, and possibly rainfall declines in Southern Australia, to increasing greenhouse gas concentrations.

The study will give wine growers a head start in developing adaptation strategies to meet evolving temperature and soil moisture shifts.

Adaptation strategies could include managing soil moisture content through increasing irrigation or mulching, vine rootstock choice, or managing crop yield. The study is also relevant to other agricultural and non-agricultural sectors.

This work was supported through the Australian Grape and Wine Research and Development Corporation [external link] and CSIRO's Climate Adaptation National Research Flagship.

Read more about Adapting to Climate Change.