Most productive wine growing regions are situated between 30 degrees and 50 degrees latitude, either north or south of the equator.
Within these temperate zones, three primary types of climates affect wine grape production.
c. Mediterranean Climates
It is often handy to classify climates as either warm or cool.
Some Other Climate Terms
The term “microclimate” is often misused to refer to a vineyard site or even a small wine region.
Bodies of water affect climate and hence wine producing conditions in many ways. The proximity of wine producing regions to bodies of water is a major theme in wine geography.
In a cold climate region like the New York Finger Lakes, the lakes store summer heat during the day and release it to warm up cooler evenings.
In the warm climate region of California’s Lake County, warm air from land rises in the afternoon and is replaced by cooler air from the lake, which cools the land.
Major ocean currents are also responsible for cooling coastal lands, which otherwise would be too hot for viticulture. The Cape Region of South Africa would be too hot but for the Benguela Current that brings in cool water from the Antarctic. The Humboldt Current in the Pacific does the same thing for Chile. The California Current swoops down from Alaska, cooling the entire Pacific Coast of North America from British Columbia down to Baja California in Mexico.
Cooling fog is an important phenomenon. In Monterey County, California, fog from Monterey Bay pushes in and down the Salinas Valley, bringing cool climate conditions to appellations like the Santa Lucia Highlands.
Rivers have long been wine producing areas. Rivers tend to retain the sun’s heat and reflect it out or up to warm adjacent vineyard areas that would otherwise be too cold.
With global warming, established wine producing regions become hotter. The risk is that the grapes will become too sweet. The yeast used in winemaking converts grape sugars into alcohol, but beyond a certain level the alcohol will kill the yeast and stop fermentation, leaving unfermented sugar. You risk too much sugar, too much alcohol, or both.
Sooner or later, what were once cool climate regions become too hot, forcing growers to change the grapes they grow, which is a problem in Europe’s highly traditional winegrowing regions. Cool climate viticulture will inexorably move to higher latitudes, north in the northern hemisphere and south in the southern. In the northern hemisphere, there is plenty of land to the north available to colonize. England, as one example, is benefiting. In the southern hemisphere, Chile and Argentina have breathing space to the south, but Australia and South Africa do not.
This is an important factor as the wine grower gauges ripening vs. acid retention. Wine grapes start off with high acidity and no sugar. As the grapes ripen, sugar increases as acidity decreases, and flavors develop. Ideally, vines will enjoy warmth and sunshine during the day, allowing them to develop their sugars and flavors through the ripening process, and then benefit from cool nights to prevent the grape from respiring too much of the valuable acidity and flavor compounds. In an ideal scenario, sugars will increase to just the right amount necessary to ferment the juice into a wine of appropriate alcohol content, acidity will decrease to a level that gives the juice a satisfying acidic pucker without burning the mouth, and flavor compounds will be optimal—all at the same time. This is the ideal time to harvest, providing that it does not rain during harvest, and factoring in the availability of labor.
We have already discussed cooling ocean fogs, but there are other factors that cool off vineyard nights.
High altitude vineyards absorb more solar radiation during the day and then cool off rapidly at night to maintain acidity. This allows the vineyards of Salta in Argentine, at 8000 feet above sea level, the world’s highest, to produce wines even though, at 25 degrees south, the region is outside of the usual 30-50 degree temperate zone. The same phenomenon favors Israel’s Golan Heights vineyards, 4000 feet in elevation.
High latitude growing areas have longer ripening days and yet greater temperature drops at night. The vineyards in Washington State, for example, see summer ripening days that are two hours longer that those of Napa or Sonoma in more southerly California. A problem in higher latitudes of course is that winter can be so cold that the vines die, an ongoing issue in Washington State.
Arid wine regions have temperature drops at night due to lack of warming humidity. Again, interior Washington State, as in Walla Walla, is an example.
Because high diurnal temperature swings are absent in the vast Central Valley of California, it is known for low quality, bulk production of wine grapes, as well as table and raisin grapes (not to mention a veritable cornucopia of other kinds of produce that do well in warm climates). In the center of the valley, the northward running San Joaquin River and the southward running Sacramento River converge into an inland delta system that significantly cools evenings, resulting in productive fine wine regions like Clarkesville and Lodi. West of this area, the Sierra Foothills counties benefit both from higher altitude and from the effect of these cooling river systems.