Of the many environmental factors which affect the productivity and quality of grape vines and their fruit, arguably the single most important variable is temperature during the growing season. Photosynthesis in Vitis vinifera is temperature dependant, and this in turn affects vegetative and reproductive growth. Different cultivars of V. vinifera have differing temperature tolerances, which largely drives the differing assemblages of cultivars observed in different wine growing regions.
Several measures have been proposed which seek to summarise the temperature records over a growing season into a single numerical value. These include the Huglin Index, Biologically Effective Degree Days (BEDD) and Growing Degree Days (GDD). Of these GDD, defined as 
To fully interpret GDD data for a particular wine growing region, it’s necessary to examine how these values change both in space and time. The Marlborough Research Centre maintains weather stations at Blenheim in the Wairau Valley and at Dashwood in the Awatere Valley. Temperature data from these two sites has been integrated with information from other weather stations by the New Zealand National Institute for Water and Atmospheric Research (NIWA). This has allowed them to produce a grid of temperature data, which has been used to produce the GDD map. This map shows the median GDD values based on data derived over a number of years.
The map shows the strong influence that topography has on growing season temperatures, with the elevated areas being markedly cooler. Although on average the Awatere Valley is slightly cooler than the Wairau Valley, there is significant variation within each of these two subregions.
Looking at annual GDD figures at particular weather station(s) brings out the growing season temperature variations associated with particular vintages. Notable are the unusually high GDD values for 1997/98 and the very low values for 2011/12. The former is probably the result of an El Niño Southern Oscillation (ENSO) event which caused New Zealand to experience an exceptionally hot summer. By contrast, 2011/12 was described by Wine Marlborough as having a summer which “never really arrived”.
For 2012/13, growing season temperatures were significantly higher than the previous year. Gapes harvested from Marlborough in 2013 totalled 251,680 tonnes, up from 188,649 tonnes in 2012. Already being called an outstanding vintage by some winemakers, WineStats will be attending the London New Release Tasting to see if 2013 exhibits high quality as well as quantity.
The area of vineyards in Chablis has expanded enormously since 1970. Then there were only 757 ha in production, but over the next 40 years this increased almost seven-fold to reach 5,043 ha in 2010. By 1995, Chablis Grand Cru and Chablis Premier Cru were both at, or close to, their maximum delimited areas. Additional growth since then has been of the less well-regarded Chablis and Petit Chablis AOPs. The Chablis AOP had a production area of 3,318 ha in 2010. Since the maximum limit for the Chablis AOP, as designated by the INAO, is 4,420 ha, there is still room for considerable future growth. Similarly, Petit Chablis’ 2010 vineyard area of 843 ha still has some way to go before the INAO limit of 1,562 ha is reached.
The increasing amount of grapes being grown in Chablis has allowed producers to ramp-up wine production. In the early 1970s, total Chablis wine production was ca. 20,000 to 40,000 hl. By 2006-2010 wine production had climbed to between 270,000 to 290,000 hl. Prior to 1970, genuine Chablis (as opposed to, say, Gallo’s “Chablis” from California) was available to only a limited number of wine drinkers. Now Chablis AOP and Petit Chablis AOP wines are produced in sufficient quantities to make them widely available in a variety of domestic and export markets.
In addition to increases in vineyard area and production, wine yield (expressed as hl/ha) has also shown a long-term upwards trend before levelling off at between ca. 50-60 hl/ha over the past 25 years. Year-on-year climatic variations certainly play a role in determining the harvest size and complicating this picture, though perhaps not quite so much as might have been anticipated. Following a series of poor harvests in 1977, 1978 and 1981, the Chablis region had a pretty good run until the heatwave vintage of 2003.
The bedrock geology of Galicia consists of Palaeozoic igneous and metamorpic rocks. Subsequent tectonic activity and weathering have produced a rugged topography with many steep slopes and deep valleys. Along the coastline many of these valleys have been drowned producing inlets or rias. Such topography means that in many areas mechanised farming is not possible, and labour costs farming terraced plots are high. Individual plots are almost universally small, with the 2009 vineyard survey showing that 97% of Galicia’s 83,942 vineyard plots were <1 ha. Producing grapes on such small plots creates something of a logistical nightmare for the bodegas and inevitably means that Galician wine producers lack economies of scale.
Of the DOPs in Galicia, only Rias Baixas has been able to increase its vineyard area to any significant extent during the 21st century. The other four DOPs are constrained by their geography and their vineyard areas have remained more or less constant. Wine production from these DOPs isn’t going to markedly increase anytime soon. So if you want to taste Palacios’ Godello from Valdeorras or Peza do Rei’s Mencia from Ribeira Sacra, you’ll have to be prepared to pay for these delights. Hopefully you’ll take some comfort from an appreciation as to why production is so limited and why their production costs are so high.
Unlike the neighbouring Galician D.O. of Rias Biaxas (whose vineyard is dominated by the white varietal Albariño), the D.O. Ribeira Sacra vineyard is dominated by black vines. White grapes have made up less than 10% of total grape production for every year this century and for the last eight years their contribution has been under 5%. The D.O. regulations permit the white varietals Albariño, Godello, Treixadura, Loreira, Torrontes and Dona Branca. Of these, Godello is the most important and typically contributes >70% of white grape production. Albarino is the second most important white grape with a contribution of ca. 15%.
The black varietal vineyard is dominated by Mencia, which has comprised >90% of black grape production every year this century. Apart from Mencia, the other recommended black grape varietals for D.O. Ribeira Sacra include Brancellao, Caino tinto, Merenzao and Souson. These varietals make up a tiny part of the vineyard and in 2012 their combined contribution was <1% of black grape production. More important is Tempranillo (also recommended) but more important still is the permitted varietal Garnacha tintorera, which made up 6% of black grape production.
Those DOPs that have been able to significantly increase their size in the 21st century are presumably enjoying a greater than average commercial success. They include well known DOPs such as Rioja (+ ca. 5,500 ha), Ribera del Duero, Rueda, Rias Baixas and Priorat. Yet the greatest vineyard gain in the 21st century has been at Extremadura’s less well known Ribera del Guadiana DOP (+ ca. 18,000 ha), Only established as a DOP in 1999, Ribera del Guadiana’s success appears to based on vinifying Tempranillo in a fruity “New World” style.