Climate categories in viticulture

In viticulture, the climates of wine regions are categorised based on the overall characteristics of the area's climate during the growing season. While variations in macroclimate are acknowledged, the climates of most wine regions are categorised (somewhat loosely based on the Köppen climate classification) as being part of a Mediterranean (for example Tuscany), maritime (ex: Bordeaux) or continental climate (ex: Columbia Valley). The majority of the world's premium wine production takes place in one of these three climate categories in locations between the 30th parallel and 50th parallel in both the northern and southern hemisphere. While viticulture does exist in some tropical climates, most notably Brazil, the amount of quality wine production in those areas is so small that the climate effect has not been as extensively studied as other categories.
Beyond establishing whether or not viticulture can even be sustained in an area, the climatic influences of a particular area goes a long way in influencing the type of grape varieties grown in a region and the type of viticultural practices that will be used. The presence of adequate sun, heat and water are all vital to the healthy growth and development of grapevines during the growing season. Additionally, continuing research has shed more light on the influence of dormancy that occurs after harvest when the grapevine essentially shuts down and reserves its energy for the beginning of the next year's growing cycle.
In general, grapevines thrive in temperate climates which grant the vines long, warm periods during the crucial flowering, fruit set and ripening periods. The physiological processes of a lot of grapevines begin when temperatures reach around 10 °C (50 °F). Below this temperature, the vines are usually in a period of dormancy. Drastically below this temperature, such as the freezing point of 0 °C (32 °F) the vines can be damaged by frost. When the average daily temperature is between 17 and 20 °C (63 and 68 °F) the vine will begin flowering. When temperatures rise up to 27 °C (80 °F) many of the vine's physiological processes are in full stride as grape clusters begin to ripen on the vine. One of the characteristics that differentiates the various climate categories from one another is the occurrence and length of time that these optimal temperatures appear during the growing season.
In addition to temperature, the amount of rainfall (and the need for supplemental irrigation) is another defining characteristics. On average, a grapevine needs around 710 mm (28 in) of water for sustenance during the growing season, not all of which may be provided by natural rain fall. In Mediterranean and many continental climates, the climate during the growing season may be quite dry and require additional irrigation. In contrast, maritime climates often suffer the opposite extreme of having too much rainfall during the growing season which poses its own viticultural hazards.
Other climate factors such as wind, humidity, atmospheric pressure, sunlight as well as diurnal temperature variations—which can define different climate categories—can also have pronounced influences on the viticulture of an area.
Wine regions with Mediterranean climates are characterised by their long growing seasons of moderate to warm temperatures. Throughout the year there is little seasonal change, with temperatures in the winter generally warmer than those of maritime and continental climates. During the grapevine growing season, there is very little rainfall (with most precipitation occurring in the winter months) which increases the risk of the viticultural hazard of drought and may present the need for supplemental irrigation.
The Mediterranean climate is most readily associated with the areas around the Mediterranean basin, where viticulture and winemaking first flourished on a large scale due to the influence of the Phoenicians, Greeks, and Romans of the ancient world.
Wine regions with continental climates are characterised by the very marked seasonal changes that occur throughout the growing season, with hot temperatures during the summer season and winters cold enough for periodic ice and snow. This is generally described as having a high degree of continentality. Regions with this type of climate are often found inland on continents without a significant body of water (such as an inland sea) that can moderate their temperatures. Often during the growing season continental climates will have wide diurnal temperature variations, with very warm temperatures during the day that drop drastically at night. During the winter and early spring months, frost and hail can be viticultural hazards. Depending on the particular macroclimate of the region, irrigation may be needed to supplement seasonal rainfall. These many climatic influences contribute to the wide vintage variation that is often typical of continental climates such as Burgundy.
There are more wine regions with continental climates in the northern hemisphere than there are in the southern hemisphere. This is due, in part, to small land mass size of southern hemisphere continents relative to the large oceans nearby. This difference means that the oceans exert a more direct influence on the climate of the southern hemisphere wine regions (making them maritime or possibly Mediterranean) than they would on the larger northern hemisphere continents. There are also several wine regions (such as Spain) that have areas that exhibit a continental Mediterranean climate due to their altitude or distance from the sea. These regions will have more distinct seasonal change than Mediterranean climates, but still retain some characteristics like a long growing season that is very dry during the summer.
Wine regions with maritime climates are characterised by their close proximity to large bodies of water (such as oceans, estuaries and inland seas) that moderate their temperatures. Maritime climates share many characteristics with both Mediterranean and continental climates and are often described as a "middle ground" between the two extremes. Like Mediterranean climates, maritime climates have a long growing season, with water currents moderating the region's temperatures. However, Mediterranean climates are usually very dry during the growing season, and maritime climates are often subject to the viticultural hazards of excessive rain and humidity that may promote various grape diseases, such as mold and mildew. Like continental climates, maritime climates will have distinct seasonal changes, but they are usually not as drastic, with warm, rather than hot, summers and cool, rather than cold, winters. Maritime climates also exist in some wine-growing areas of highlands of subtropical and tropical latitudes, including the southern Appalachian Mountains in the United States, the eastern Australian highlands and the central highlands of Mexico.