Continentality

Continentality is the tendency of land to experience more thermal variation than water, due to the land's lower specific heat capacity. Continental climate also tends to be dryer than oceanic climate as there is less moisture input to the atmosphere from evaporation. Because temperature and moisture content are key factors in influencing regional climate, continentality affects and influences both temperature and precipitation.

This causes localised as well as global effects on weather patterns. For instance, high pressure caused by cold, sinking air over Siberia in winter and low pressure caused by warm, rising air over Siberia in summer help drive the monsoons of South Asia.

A characteristic of regions that lack the temperature moderating effects of the sea and that exhibit a greater range of minimum and maximum temperature, both daily and annually.

The sea itself has its own weather pattern. Winds and currents range depending on the ocean. Land near the sea share its patterns, whereas further away the land begins to develop its own weather patterns.

Continentality is the reverse of water moderation. Mean daily range (MDR), the difference between the mean maximum and the mean minimum temperatures, estimates continentality.

Temperatures in continental sites are more variable and extreme. In summer, continental sites receive more heat to assist fruit and vine maturation, but they also have increased hazard from other related weather events characteristics of continental sites which interfere with grapevine function.

Water moderates both summer and winter temperatures

Water moderation (less continentality, lower MDR) increases the length of the growing season. In the fall, continental sites have greater temperature fluctuation meaning higher day temperatures and lower night temperatures. This aids fruit maturation, but should the temperature drop below 28°F, foliage is killed and the season is abruptly terminated. This not only interferes with fruit maturation, but it can prevent the achievement of potential grapevine cold hardiness.

Where MDR is high, the probability of spring freeze increases. In the spring when the temperature is 50°F or more, buds begin to develop. High MDR sites experience more frequent high temperatures which promote early bud growth and more frequent low temperatures which may cause freeze injury. The primary benefit of water moderation to NY sites is reduced winter cold hazard. The water moderation provides an additional benefit of reduced low spring and fall freeze hazard. More continental sites may require freeze protection (sprinkle irrigation, wind machines or heaters) in the spring, early summer and fall to prevent freeze injury to green tissues.

Low temperature hazard is primarily related to latitude. At northern latitudes water moderation is required for winter cold moderation. Northern European vine production benefits from the moderating influence of the Atlantic Ocean and especially of the Gulf Stream. (Note relatively high December, January and February expected monthly low temperatures in Bordeaux France relative to the North American sites, and that the very continental Fairmont, MN, also stands out as having more extreme temperatures. In the latter case the problem is both variable temperatures and low total heat supply.) Water moderation that reduces continentality facilitates grape production at higher latitudes.

In summary

To reiterate, a site with a continental climate has a high MDR. This means more heat to assist fruit maturation. The day and night temperatures during the September-October period have a very important impact on fruit composition and wine quality. However, a continental climates also has greater winter cold injury hazard, induces spring bud growth before the freeze hazard has ended, and experiences earlier fall freezes than water moderated sites.

Go to NY Map with Cold Isotherms

The map shows expected minimum temperatures in NY. Note the relationship between large bodies of water (Lake Erie, Lake Ontario and Long Island Sound) and the expected cold temperature. The topography is also important. The low elevation sites in the Finger Lakes and the Hudson Valley are warmer than the adjacent highlands.

See also

• Climate categorizations in viticulture