Climate is the weather of a particular place over a long period of time. And it is arguably the single, most-important factor determining the character of fine wine from any given region. Climate largely determines which grape varieties are viable, how ripe they usually get, and if there will be significant vintage variation. We often hear that California’s top wine regions have a Mediterranean climate, but what does that mean?

Climate Categories

There are several climate classification systems. In the United States, people in the wine industry often refer to Winkler-Amerine heat summation. But that only takes one factor into account—daily maximum temperature during the growing season. There are many other important factors to consider, including average daily temperature, cloud cover, variation of temperature throughout the year, amount and seasonality of precipitation, and humidity. 

The Köppen classification system is one of the most popular with climatologists not focused on a particular industry. It starts with five broad categories.

Tropical: hot and rainy every month of the year

Dry: very low rainfall, regardless of temperature

Temperate: moderate winters and seasonality—the coldest month averages between 27° and 64.4° F and at least one month averages more than 50°F

Continental: cold winters and pronounced seasonality—at least one month averages below 27° F and at least one above 50°F

Polar/Alpine: always cold—every month averages below 50°F

These categories each have two or more subcategories, 27 in all. Though grape growing is conceivable in most of them, the vast majority of high-quality vineyards have either Continental or Temperate climates. Temperate has nine sub-types, but the most common for wine regions are Maritime (Oceanic), Warm-Summer Mediterranean, and Hot-Summer Mediterranean.

Continental climates have pronounced seasonality, but rain falls more or less equally throughout the year. There’s often significant frost risk during spring. Summers are warm and humid. Autumn is generally cool, which means vines and grape bunches don’t dry quickly, if at all, after storms. All this leads to a relatively short growing season.

Maritime climates have less seasonality than Continental climates. There’s typically no significant difference in rainfall between seasons. Growing seasons are longer than in Continental climates. However, given the ongoing precipitation and related cloud cover, the growing season is cloudier and shorter than in Mediterranean climates. This type of climate, influenced by stormy oceans, features considerable variation in weather from one year to the next.

Mediterranean climates are temperate with a long, dry, and sunny growing season, due to the moderating influence of a large body of water. Most rain falls during winter. Achieving ripeness is relatively easy and disease pressure is low. The weather in these climates is very consistent from year to year.

Climate Types by Wine Region

In reality, few regions are purely one climate type or another. One type predominates, but there may be influences of another, due to factors such as mountains or a distant body of water. Here are some examples of  wine regions with non-Mediterranean climates.

Austria – Continental
Burgundy, France – Maritime with Continental tendencies
Bordeaux, France – Maritime
Champagne, France – Maritime with Continental tendencies
Hunter Valley, Australia (New South Wales) – Maritime
Mendoza, Argentina – Hot-Desert Dry with Continental tendencies
Mosel, Germany – Maritime with Continental tendencies
New Zealand – Maritime
Northern Rhone, France – Continental with Mediterranean influence
Rias Baixas, Spain – Maritime
Rioja, Spain – Continental with Maritime influences
Toro, Spain – Continental
Sancerre, France – Maritime with Continental tendencies

Mediterranean Climate

The three sub-types of Mediterranean climate are distinguished by their summer temperatures: cold, warm, and hot. The cold variant is only found in a handful of places in the world, none of which produce wine. There are a lot more Hot-Summer Mediterranean climates than Warm-Summer.

Mediterranean climates are very rare overall. Only 2% of Earth has some form of Mediterranean climate. But their prevalence among fine wine regions is much higher. Here are some examples.

Hot-Summer Mediterranean climate wine regions

Barossa Valley, South Australia
Campania, Italy
Central Valley, California
Greece
Jerez, Spain
Lebanon
Tuscany, Italy
Sardinia, Italy
Sicily, Italy
Portugal (southern)
Stellenbosch, South Africa
Swan Valley, Western Australia
Walla Walla, Washington

Warm-Summer Mediterranean climate wine regions

Central Chile (coastal)
Coastal California
Coonawarra, South Australia
Margaret River, Western Australia
Adelaide Hills, South Australia
Portugal (Northern)
Swartland, South Africa
Willamette Valley, Oregon

What a Mediterranean Climate Means for Wine Growing

Warm-Summer Mediterranean climates are the most versatile of wine regions, in terms of the number varieties which can succeed and the range of styles which they can produce. The long, sunny growing season gives vines an early start and allows vigneron to let late-ripening grapes hang into November (May in the southern hemisphere). The long season leads to excellent color, soft tannins, and well-developed flavors. In which are on the cool side, or in which temperatures drop dramatically at night, the ripeness doesn’t necessarily mean a shortage of acidity.

Mild, and typically dry, weather during Spring allows bud break, flowering, and fruit set to occur without mishap. Low rainfall, and relative lack of humidity in most of these regions, during the growing season limits risk of rot and mildew. Therefore, yields are typically both good and predictable. There’s also minimal need for spraying.

All of these positive factors taken together mean producers can make wine in the style they choose, not just that which the weather allows. A single site might produce both high- and moderate-acid Chardonnay, another both medium- and full-bodied Cabernet Sauvignon.

Variation between Mediterranean climate regions

Within both the Hot-Summer and Warm-Summer sub-types, there can be significant climate-related differences from one growing region to another, especially in humidity and daily average temperature. This is normally due to local factors such as latitude, mountains, and distance from the sea. 

Santa Maria Valley and Oakville are both Warm-Summer Mediterranean climate regions. But they vary substantially in average daily temperature. The Santa Maria Valley AVA begins about seven miles from the Pacific Ocean and there are no mountains to block the cold, sea breezes. Oakville is separated from the ocean by about 35 miles and three mountain ranges. Therefore, westernmost Santa Maria Valley is best-suited to grapes such as Chardonnay and Pinot Noir and only the easternmost vineyards can achieve ripe, medium-bodied Cabernet Sauvignon. Oakville, on the other hand, easily produces lush Cabernet Sauvignon, but isn’t especially well-suited to Chardonnay or Pinot Noir.

Copyright Fred Swan 2019. All rights reserved.