Climate Classification: California heat summation

The first extensive practical use of de Candolle’s method was in California, where amerine and winkler, in 1944, delineated five viticultural regions on the basis of their Fahrenheit temperature summations over 50 °F/10 °C. One advance over de Candolle was to confine the summations to a fixed vine growth and ripening season extending from 1 April to 31 October.

The California summations (like most others) are in practice calculated from monthly averages of maxima and minima, each month’s total being its average excess of the mean over 50 °F, multiplied by the number of days in the month. Amerine and Winkler proposed five regions for California based on heat degree days (HDD) but more recent studies of temperature conditions in western US vineyards by Jones et al. (2010) and in New Zealand by Anderson et al. have identified the need to update this classification by creating additional classes at both the lower and upper ends, as shown in the table below, since the original classification did not encompass present cool and hot limits.