Viticulture Versus Climate Change

When the general and business press approach the topic of climate change as it relates to wine production, apocalyptic predictions for established areas are not uncommon. Scenarios include radical changes in wine styles, the development of new wine regions, replanting with new varieties and so on. However work is ongoing to fully understand this process of change. Less "nuclear" responses are also being researched.

Concerns over climate change have certainly heightened interest among academics and the wine industry in gaining a fuller understanding of how the timing of key events in seasonal cycles varies between varieties. Phenology is the study of periodic life cycle events of plant and animal life. It covers how these are influenced by seasonal and year-by-year variations in climate, plus habitat factors such as altitude, aspect and slope. It is one of the key indicators of climate change. With respect to grape growing, key phenological stages include flowering, veraison and ripening.

Dr Amber Parker, a senior lecturer in viticulture at Lincoln University in New Zealand, is a leading researcher in this field. She initially completed a masters degree in France in 2008, and then a PhD at Lincoln, where a core focus of her research is modeling the differences in phenology of different grape varieties.

Parker is also at the forefront of research into methods to mitigate the effects of climate change in the vineyard. Her PhD thesis continued her previous work, and examined aspects of canopy management and how they might affect the timing of key stages in the grapevine growing season.

Grapevine phenology and harvest dates

Particularly in a well-established wine country like France, grapevine phenology is a large factor determining which grape varieties are planted in a given wine region. It provides well-documented markers to inform the calculations of winegrowers.

Studies in this area are underpinned by year-by-year viticultural records of when particular growth stages have commenced in the vine, or when particular tasks have been undertaken. These are often large datasets; in some European locations wineries have sets of ledgers reaching back to the 14th Century. Currently, downscaling studies are going deeper than the regional level, to look at vineyards, blocks, and even the slight differences between individual vines.

A focal point of concerns is that warmer temperatures continue to bring forward harvest dates to a point when berries would be ripening during the warmest temperatures of summer. This could have a major impact on flavour and aroma and other characteristics of the harvested fruit and consequently the style of finished wines. In the "mainstream" latitudes for grape growing, grapes ripen through the summer and into the autumn when they are harvested. Therefore the last stages of ripening occur as temperatures begin to cool.

The work of Parker and her colleagues has specifically looked at phenological models for wine grapes.

"Using average annual temperature as a driver, models of flowering and veraison were constructed for over 100 varieties. This data could be used to back-calculate phenology for different varieties based on a set rise in average annual temperatures. Among other outcomes this could suggest what varieties could be most suited to future temperature projections."

This work continued for several years and has resulted in a 2011 paper outlining the model developed.

Further work resulted in another paper in 2013. This used the database created in the 2011 study and subsequent data validations and phenological observations to outline a classification methodology for the timing of flowering (for 95 varieties) and veraison (for 104). This can be used to assist choosing varieties for planting new vineyards, and may inform the breeding of new varieties.

Climate change scenarios vary greatly across different wine regions, in terms of levels of change and threat. The diversity of Vitis vinifera does at least allow plenty of flexibility. The top 10 grape varieties by planted vineyard area account for 71 percent of the total expanse. There are another 1000 or so wine grape varieties grown on some kind of commercial scale so, in basic terms, there is plenty of room to maneuver.

Non-nuclear options for combating climate change

Changing grape variety in a vineyard is nevertheless expensive. Regaining previous yield levels will take 4-5 years if replanting, or 2-3 if re-grafting in the field onto established rootstocks. Other shorter term, adaptive strategies are possible. This has been another area of interest for Parker. Her PhD thesis focused on manipulations of the vine canopy that may affect the timings of key stages within the growing season. In particular she looked at different ratios of leaf numbers vs bunch numbers to see whether and how far ripening could be pushed back. The results of this work have been promising. Delays in veraison of up to one week have been achieved, which in turn change how quickly sugars are accumulated in the grape.

Other types of manipulation are being investigated by other academics. Late pruning may delay the developmental cycle of the grape vine. Other studies are looking at the development of sprays containing plant growth regulators. Beyond canopy management, research is being undertaken into whether changing rootstocks may be a longer-range option, and modifications to irrigation a more short-term one.

Delaying pruning throughout the winter until just before predicted budbreak can produce a significant delay. This is practiced in some northern vineyards to avoid spring frosts, but may also have benefits for delaying ripening in warmer climates.

Choices regarding adaption strategies are not going to be the same in all regions. Manipulations such as those mentioned above need to be matched to a range of other factors. For example, vine canopy leaf removal might in some cases leave insufficient shade and lead to heat stress.

Today, part of Parker's focus is dealing with the effect of the aforementioned leaf removal actions on aroma and flavour. She is working with various international groups on downscaling climate and phenological models. 

Of course, wine regions are not experiencing equivalent symptoms of climate change, and weather and rain patterns can be markedly different, as well as temperatures. Moreover, as my discussion with Dr Parker made clear, the picture can vary according to grape variety, region and management, and actions required may not always be drastic.

Climate change is a fact; countless phenological studies unambiguously demonstrate this. But hearing about her research also showed me that the effects of that change on the wine industry will be more nuanced and not always as gloomy as those apocalyptic headlines would suggest.