Climate heats up, grapes ripen sooner

A study of vineyard records attributes the earlier ripening of wine grapes 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. Published in the journal Nature Climate Change, the study was conducted by scientists from the University of Melbourne and Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO). Climate scientist and viticulturist Leanne Webb says that while trends towards earlier ripening have been widely reported, a detailed study of the underlying causes of these shifts has not been previously undertaken. “Changes to the timing of biological phenomena such as flowering and emergence of butterflies have been noted on many continents over recent decades. In some wine-growing regions such as southern Australia, grape maturation dates have advanced about eight days per decade, with earlier maturing potentially impacting wine-grape quality and regional branding,” Webb says. “This has been a study of potential influences on wine-grape maturity trends on a continental scale. 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, 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. These strategies could include managing soil moisture content through increasing irrigation or mulching, vine rootstock choice, or managing crop yield.” “This study analyzed harvest diaries from southern Australia for periods of up to 64 years. 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.” “The study centered on 10 winegrowing sites in four states. These sites had records of observations for periods of more than 25 years. Nine of the ten sites had trends to earlier ripening. Only one Margaret River vineyard in Western Australia ripened later.” “In addition to informing the wine industry of adaptation options, we believe our study is also relevant to many other agricultural and non-agricultural sectors where trends in timing of biological phases have been detected,” says Webb. The paper was supported by the Australian Grape and Wine Research and Development Corporation and CSIRO’s Climate Adaptation National Research Flagship.