Daily Temperature Data
Air temperature is the single most important environmental factor influencing a vineyard, thus it should be a major consideration in vineyard site selection. When evaluating a potential site, recognize that topography, elevation, slope, and aspect interact to influence temperature variations within a site. Air temperature directly influences the rate of grapevine growth and fruit development. Of particular importance is the influence of summer heat, both daytime and nighttime temperatures, on grape maturity and quality. The growing degree-days system for grapes, developed by Amerine and Winkler, was used as the basis for dividing California into five winegrape producing regions. Grape varieties were recommended for the climatic regions based on degree-days, ripening season, performance in the vineyard, and subsequent wine quality. Several more elaborate methods have been developed that are intended to assist growers in characterizing the climate of their location compared to known winegrape production regions as universal guides to selection of adapted varieties.
Damaging low temperatures are also of great concern to grape production. This includes the potential for frost in late spring or early fall, and winter injury due to low temperatures. See Grapevine Cold Hardiness for more information on cold temperature injury.
