Growth and development of plants, insects and other invertebrates depends largely on the temperature from. Many of these organisms slow or block their growth and development as temperatures rise or fall above or below certain threshold levels. All plants need a certain individual temperature sum in order to be ready for the blossom to be. The accumulation of thermal energy over a given period of time is referred to as the degree of growth days or the sum of the sums of heat (heat sums). It is a heuristic (as opposed to logistic) calculation in the phenology,
As a rule, WGTs are calculated by taking the average of the daily minimum and maximum temperatures and comparing them with a threshold (in Central Europe 10 ° Celsius). The measurement of growth grade days and temperature totals is used to establish planting data, to predict the flowering and optimal harvest timing, and to select the most suitable one varieties depending on their phenological Maturity date (early to late).
The development of insects and mites also depends significantly on the daytime temperature. A simple determination of temperature sums can be related to plant protection be useful in predicting the outbreak of various pests under glass; and to derive the exact date of use of suitable control agents or measures. The first scientific study on the climatic influence on viticulture is by the Swiss botanist Augustin Pyrame de Candolle (1806-1893).
Based on these findings, in California by Albert Julius Winkler (1894-1989) and Maynard A. Amerine (1911-1998) carried out an analysis, the results of which in 1944 led to the introduction of a heat accumulation system and classification into five climatic zones. In the meantime, many wine-growing countries have similar air conditioning systems introduced. See also below Weinbauwürdigkeit,