There is increasing evidence that warming trends have advanced wine grape harvest dates in recent decades (14,23). Across the globe, harvest dates advance approximately 6 days per degree of warming. Harvest dates are closely connected to the timing of grape maturation, which is highly sensitive to climate during the growing season. Specifically, warmer temperatures accelerate grapevine phenology over the full cycle of development (budburst, flowering, veraison and maturity), whereas increased precipitation tends to delay wine grape phenology (15). The earliest harvests thus generally occur in years where the growing season experiences warmer temperatures and drought (16).
During cool seasons the amount of heat units is lower than the specific culture requirements, resulting in delayed vine phenology and unripe grapes (i.e., low sugar contents, high acidity levels). During cool seasons, grapes will struggle to achieve the necessary sugar content as required under appellation regulations. By waiting for adequate sugar contents during cool seasons, they are exposed to other climatic risks, particularly the arrival of autumn rain. Higher heat units favor vine phenology, grape ripening, and wine quality. With too many heat units, however, vine phenology and grape ripening evolves very rapidly. Very high sugar loading and rapid acid degradation during grape ripening leads to wines having high alcohol contents, low acidity levels, and unfamiliar flavor profiles (23).
High-quality wines are typically associated with early harvest dates in many of the cooler wine-growing regions, such as France (17), and are also favoured by warm summers with above-average early-season rainfall and late season drought. Overall, both precipitation (18) and temperature (19) contribute to wine quality and the timing of harvest (20), although temperature is the most critical factor influencing wine grape phenology (21).
Most research on the relation between climate and wine grape harvests has focused on relatively short, recent timescales, for example the past 30-40 years. Recently, over 400 years (1600-2007) of harvest data from Western Europe (France and Switzerland) have been analyzed. These data have been compared with (reconstructed and measured) data on temperature, precipitation and soil moisture over this period (13).
In this historical record, years with the latest and earliest harvest date were 1816 and 2003, respectively. 1816 was the so-called ‘Year without a Summer’ following the eruption of Mount Tambora in Indonesia. This eruption caused pronounced cooling over continental Europe during the growing season, with harvest dates delayed over three weeks. 2003 was one of the worst summer heat waves in recent history. Compared with the variability of harvest dates from one year to another in this historical record, average harvest dates were substantially earlier (about 10 days) in more recent decades (1981–2007) than in the previous 400 years (13).
Historically, high summer temperatures in Western Europe, which would hasten fruit maturation, required drought conditions to generate extreme heat. The relationship between drought and temperature in this region, however, has weakened in recent decades and enhanced warming from anthropogenic greenhouse gases can generate the high temperatures needed for early harvests without drought (13).
Grape harvest date and wine quality depend on a number of factors beyond climate, including wine grape varieties, soils, vineyard management, and winemaker practices (22). The analysis of the historical record suggests, however, that the large-scale climatic drivers within which these generally local factors act has fundamentally shifted. Such information may be critical to wine production as climate change intensifies over the coming decades in France, Switzerland, and other wine-growing regions (13).
The nature and trends of climate variables and bioclimatic indices have been analyzed for 6 locations situated in the Loire Valley, northwest France, along with the berry composition of the 6 main grapevine varieties cultivated there, from 1960 to 2010 (4). Results show significant increases in mean temperature (by 1.3 to 1.8°C) over the growing season (April to September) throughout the Loire Valley, with maximum temperatures increasing more strongly than minimum temperatures. Temperature variables, such as spring and summer temperatures, the number of days with maximum temperatures >30°C and bioclimatic indices increased significantly (3).
The berry composition of the 6 main white and red grapevine varieties changed significantly, with higher sugar concentrations and lower titratable acidity at harvest. It was concluded that these changes in berry composition were significantly influenced by the increases in temperature over the study period. Harvest dates advanced by 2 weeks on average (3).
In France in the Bordeaux region, Loire Valley and Rhone Valley, most of the winemakers have noticed an improvement in quality of wines for the past 10–20 years (12).
In one of the five wine-growing sub-regions of the Loire Valley region, Anjou-Saumur, annual and growing season average temperatures increased by 1.5 and 1.7 °C, respectively, from 1950 to 2010. Earlier phenological stages and harvest dates (14 days earlier on average) were observed, along with higher sugar contents and lower acidity levels in grape berries at harvest. Overall, recent temperature increases have been favorable for grapevine behavior and wine quality in this sub-region (23).
Meteorological data recorded since 1972 in Colmar (Alsace, France) have been analyzed and compared with data on grapevine budburst and harvest (Vitis vinifera cv. Riesling, a representative variety of the Alsatian grape industry). Since 1972 a significant increase in temperatures was observed. Phenological data recorded on local grapevine collections over the same period show that the period between budburst and harvest has become both earlier and shorter. A comparison of climatic and phenological data shows that ripening is occurring under increasingly warm conditions. The climatic water demand after flowering tends to increase and, as there is no clear evidence for a change in rainfall, the risks associated with dry summers are likely to increase in the future (1).
If higher temperatures initially improve ripening and thus lead to better quality wine, in the long term, with a continuous increase, they could result in a change in the aromatic profile of wines produced in Alsace and elsewhere. The exceptionally warm and early growing season in 2003 is an experience on a large scale of what could become normal conditions (1).
Roussillon is a wine-producing area in southern France. It is situated in the larger region Languedoc-Roussillon, near the city of Perpignan. Languedoc-Roussillon remains the largest wine-producing region in France by both area and volume, with viticulture accounting for one third of agricultural land in 2010 (5). The warm and dry conditions of 2001–2010 have already had negative impacts for producers in Roussillon, and projections suggest that the drying trend will increase in the future. Climatic change will affect both grape yields and wine quality (4).
Impacts on yields
The main concern of producers is excessive summer water stress, leading to decreasing yields. It was estimated that yields in Languedoc-Roussillon could decrease by 26% by 2080 due to increased water stress alone (6). This is due to three climatic effects (7):
- higher temperatures lead to an accelerated phenological cycle and thus to a shorter growing season and a biophysical decrease in yield;
- a decrease in summer rainfall impacts on grapevine vigor and berry weight, especially for soils with low water-holding capacity. Disturbances to autumn, winter and spring rainfall patterns limit aquifer recharge and results in premature soil profile desiccation, which can negatively impact on berry size;
- the accumulative effects of increasing temperatures and decreasing rainfall leads to higher evapotranspiration demand, and thus to higher water consumption by vines.
Impacts on the quality of harvest
Night temperatures during maturation are particularly important influences on quality. An increase in minimum temperatures during the growing season can have a negative impact on aromas and tannins, and thus on vintage quality (8). In August, from veraison to harvest, warm nights expose grapevines to a risk of a block in phenolic maturation, leading to excessive berry sugar content, which leads in turn to a need for post-harvest manipulation such as de-alcoholization (9).
For the Alsace it was concluded that likely changes in environmental conditions will necessitate some adjustments to preserve certain specific characteristics of the wines produced in Alsace: a different choice of the plant material; modified training systems, in a broad sense, from soil management to canopy architecture; and considering new areas, at higher altitudes, for example, since they might be suited to the production of good quality wines (1).
In the national strategy of France the following adaptation measures are recommended (2):
- carry out genetic research for new grape varieties suited to the lands;
- perfect new irrigation technologies.
Roussillon: options and constraints
With the current level of adaptive capacity, climate change could heavily penalize Roussillon’s wine industry by the end of the twenty-first century, increasing the challenge for the local industry to compete with other French regions or internationally. Where nations have more liberal vineyard management practices, quality regulations and adaptation options, they may be more flexible in the face of change, even if they also are likely to face their own adaptation challenges (10).
Drip irrigation can be an efficient technique to compensate for an increased water deficit in Mediterranean vineyards (11). However, several factors hinder the development of irrigation in Roussillon (4):
- groundwater and surface water resources are limited in the hilly areas and are already in strong competition with both fruit production in valley areas and with urban uses along the coast;
- almost two millennia of grape growing in Roussillon have resulted in highly fragmented blocks, a situation that poses technical problems for the implementation of a collective irrigation system. Furthermore, the current marketing strategy of terroir wines and the broader economic situation do not encourage any restructuring of the blocks;
- until the 1970s Roussillon’s valley-floor vineyards were often flood-irrigated to produce high-yielding but low-quality grapes. As a result, there is a lack of an historical cultural acceptance of the advantages of controlled deficit irrigation to produce premium wine.
Moving of blocks
One option for producers to adapt to future climatic risk might involve the purchasing of more blocks in areas considered as potentially optimal in the next decades and the selling of blocks more exposed to negative changes in climate. However, current AOC regulations limit the spatial expansion of wine-producing areas (4).
The choice to cultivate a particular variety of Vitis vinifera depends not only on trends in consumer demand and suitability to the local bioclimatic conditions, but also on AOC regulations. Current AOC legislation for Côtes-du-Roussillon-Villages established the use of two or more varieties to produce classified red wine: one variety must be either Grenache and Syrah, and the other Carignan or Mourvedre. Again, appellation rules may need to evolve in an iterative manner to support long-term adaptation (4).
Autonomous adaptation by winegrowers’ decision-making is an ongoing process, depending on many climate and non-climate-related factors (23).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for France.
- Duchêne and Schneider (2005)
- ONERC (2007/2009)
- Neethling et al. (2012)
- Lereboullet et al. (2014)
- Onivins (2011), in: Lereboullet et al. (2014)
- Garcia de Cortazar (2006), in: Lereboullet et al. (2014)
- Payan et al. (2011), in: Lereboullet et al. (2014)
- Tonietto (1999); Mori et al. (2007), both in: Lereboullet et al. (2014)
- Attia (2007), in: Lereboullet et al. (2014)
- Bardsley and Pech (2012), in: Lereboullet et al. (2014)
- Brisson et al. (2011); Gladstones (2011), both in: Lereboullet et al. (2014)
- Bonnefoy et al. (2013)
- Cook et al. (2016)
- Jones and Davis (2000); Duchêne and Schneider (2005); Seguin and de Cortazar (2005); Schultz and Jones (2010); Tomasi et al. (2011); Camps and Ramos (2012); Webb et al. (2012), all in: Cook et al. (2016)
- Jones et al. (2013), in: Cook et al. (2016)
- Jones and Davis (2000), in: Cook et al. (2016)
- Jones and Davis (2000); Jones et al. (2005), both in: Cook et al. (2016)
- Van Leeuwen et al. (2009), in: Cook et al. (2016)
- Baciocco et al. (2014), in: Cook et al. (2016)
- Camps and Ramos (2012); Webb et al. (2012), both in: Cook et al. (2016)
- Jones et al. (2005), in: Cook et al. (2016)
- Jackson (1993); Van Leeuwen et al. (2013), both in: Cook et al. (2016)
- Neethling et al. (2017)