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Central Otago’s vine climates
The decision in the 1970s to dam the Clutha River and build a hydroelectric power station near Clyde was highly controversial. Sluicing for alluvial gold from the 1860s, followed by dredging for gold in the twentieth century, had already degraded the lowland landscape of much of Central Otago. Locals were polarised by the prospect of their unique landscape and close communities being split and divided by a 50-kilometre lake from the dam at Clyde to the Loop Road, Bendigo. Construction finally commenced in 1982, the dam was commissioned in 1992, and Lake Dunstan filled in 1993. At the junction of the Clutha and Kawarau rivers the lake flooded the lowest and oldest part of the historic mining town of Cromwell. It also affected the narrow Kawarau Gorge that links Cromwell with Arrowtown and Queenstown.
The National government of the 1970s and early 1980s and the Labour government from 1984 placated Central Otago’s rural population by providing funds for a joint study by the Ministries of Agriculture and of Works to investigate the possibilities of intensifying the rural production of Central Otago. Scientists in the regional offices of these two central government agencies focused on establishing the temperature and wind patterns along the upper Clutha and Kawarau rivers. Grapes were included as one of the main crops to be considered, although the weather and climate information which was compiled could be applied to a variety of annual and perennial crops. MAFTech’s Gordon Cossens organised much of the data collection and analysis and was lead author on most of the reports.
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This detailed scientific work was disseminated in a series of publications that were printed sub-region by sub-region as the research was completed. Those contemplating winegrowing in Central Otago, including local landowners, devoured the information. The strength of the research derives from the close network (‘swarm’ in the climatological jargon) of temporary climate stations the researchers established in each sub-region. The fine resolution of the network, when integrated with the longer climatic record of the meteorological stations of Central Otago, established the seasonal temperature regimes and wind patterns of the localities where grapes might be grown. The topoclimatological studies identified potential vineyard sites in new localities – notably in the Lowburn area, on both sides of Lake Dunstan, near Bendigo, as well as at Bannockburn and the higher terraces along Lake Dunstan. No other wine region in New Zealand had such a comprehensive analysis of its weather and climate.
By the early to mid-1980s, empirical knowledge of the performance of different grape varieties was accumulating rapidly among the first group of wine enterprises and could be generalised and verified against the detailed information from the data collected by Cossens and others. By the early 1990s, the second wave of aspiring winegrowers such as Stewart Elms, the Dicey family and Steve Green of Carrick were able to differentiate
Cossens’ research demonstrated that the accumulation of energy over the growing season varies considerably from one locality of Central Otago to another (Table 8.4). Two of the three places where grapes were already planted (Gibbston and Wanaka) both accumulate fewer than 950 degree-days over the growing season, whereas Alexandra (1030) and Bendigo (1040) receive appreciably more solar energy. The results from Bannockburn are even more persuasive. Its degree-days during the growing season are at least 350 higher than Wanaka and Gibbston and more than 150 higher than all other districts. The conclusion is clear: the first plantings in Central Otago were not in the most favourable places for coaxing grapes to reach physiological maturity.
One caveat needs noting. The low night temperatures of Gibbston and Wanaka are the main influence on reducing their average temperatures. Daily highs are much more similar across all of these sites. The same is true of Bendigo. Such high diurnal ranges of temperature encourage the development of flavour compounds as the berries of Pinot Noir ripen. Nevertheless, the differences in day/night temperatures of these first vineyards is not sufficient to change the general conclusion that other parts of Central Otago had climatic advantages over Gibbston and Wanaka for growing grapes. However, any environmental disadvantages became less significant as the Central Otago wine region matured. Wineries in the Kawarau Gorge could diversify their sources of grapes by buying or growing them in sub-regions such as Bendigo or Bannockburn where the probabilities of ripening grapes every year are higher. Moreover, Gibbston and Wanaka had other advantages that compensated for their climatic limitations. In both summer and winter, vehicle traffic counts are much higher through these localities than other rural parts of Central Otago. Wineries in the Kawarau Gorge benefit hugely in both their tasting rooms and restaurants from direct sales to this passing traffic.
The Cossens publications became available between 1985 and 1990 when the interest in planting vines was about to take off. From about 1995, when fewer than 50 hectares were planted, the area in vines in Central Otago increased sharply (Table 8.5). By 2000 it had reached 280 hectares and by 2005 this had more than tripled to 978 hectares. By 2010 it was 1540 hectares with Pinot Noir making up 78 per cent of the total area in vines. During this rapid expansion, Pinot Noir vineyards appeared on a much wider range of sites. Cossens’ work had alerted many of the new and established grape growers to the environmental advantages of these alternative sites. They were able to make more informed choices on where to plant Pinot Noir. New vineyards appeared on the western side of Lake Dunstan in localities from Queensbury to the outskirts of Cromwell. On the eastern side of the lake, Ardgour, Bendigo Station (the Loop Road and the Terraces) as well as Cairnmuir and Bannockburn have all become important concentrations of vines.
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