Plains appears to have the potential for viticulture, such conditions make choosing appropriate sites essential. In addition, competition from other systems of agriculture, such as dairying on irrigated land, has resulted in increased land values in Canterbury.
The map of annual hours of bright sunshine adds further insights into the atmospheric conditions of regions where grapes are now grown (Figure 4.7). The isoline of over 2000 hours of sunshine annually includes the areas where over 90 per cent of New Zealand grapes for wine are planted. It encompasses the large regions, Hawke’s Bay and Marlborough, but also Gisborne, Nelson, Waipara and Central Otago. It also distinguishes the middle and upper Waitaki Valley, Mackenzie Basin (where grapes have been planted) and other parts of south and central Canterbury as potential areas for vines.
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In the South Island, Nelson and Marlborough stand out from the rest because both have substantial areas with more than 2200 hours of sunshine annually. In Nelson’s case, these higher sunshine hours partly offset its noticeably higher annual precipitation and humidity compared with Marlborough. As with most climatic measures, hours of sunshine also show a definite west to east gradient.
Comparison of temperature curves of the French ‘cool climate’ wine regions with the New Zealand regions reveals one important difference (Figure 4.8). New Zealand temperature curves are noticeably flatter in all parts of the country but especially in the North Island. The steeper French curves means that annual temperature ranges are greater in France than in New Zealand. Some French regions, such as Bordeaux, have both higher temperatures in summer and lower temperatures in winter. These same generalisations apply to the growing season for the vine, usually defined as April to October in the northern hemisphere and October to April in the southern.
Winters are much warmer in most parts of New Zealand with the result that temperature curves are much flatter. In other words, annual ranges of temperature are noticeably lower in New Zealand. Again, this results from the influence of maritime conditions on the climate and weather of the country. Air masses crossing New Zealand are always influenced by their passage over water. This tends to suppress the extremes, cooling the air masses in summer and warming them in winter. Middle-latitude France and Mediterranean Europe are exposed to the continental influences of both Africa and Eurasia and have noticeably hotter summers and colder winters.
Damian Martin, a New Zealander who completed his doctoral work under Professor Gerard Seguin in Bordeaux, and former CEO of the Marlborough enterprise ARA, expresses clearly why a climate that is both cool and dry extends the window for picking until the berries have reached optimum ripeness: