Calwineries

UC Davis Heat Summation Scale

The Use of the UC Davis Heat Summation Scale in California

The UC Davis Heat Summation Scale is a rough but useful guide to which varietals will thrive in California Wine Country . The whole system rests on the concept of the “degree day.” Between April 1st and October 31st, the number of degrees is equal to the average daily temperature minus 50. 50 degree Fahrenheit is the minimum temperature for grape growing.

The UC Davis heat summation scale is organized into five tiers. Region I is the coolest and Region V is the warmest. The following is a list of the recommended varietals to grow in each region:

• Region I: Below 2,500 degree days; Chardonnay, Pinot Noir, Gewurztraminer, Riesling
• Region II: 2,500-3,000 degree days; Cabernet Sauvignon, Merlot, Sauvignon Blanc
• Region III: 3,000-3,500 degree days; Zinfandel, Barbera, Gamay
• Region IV: 3,500-4,000 degree days; Malvasia, Thompson Seedless
• Region V: Over 4,000 degree days; Thompson Seedless, other table grapes

When speaking about climate, it is important to distinguish the size of the area you are referring to. While entire regions are generalized by the UC Davis heat summation scale, there are often major differences within these areas.

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