Bioclimatic Indices
This page shows the progression over time of some bioclimatic indices used in viticulture.
Bioclimatic Indices - VINE
Each of the speedometer or gauge charts (at the top) represent the current status of progress of the bioclimatic indicators (current value).
Each index has its specific calculation period during which its value evolves over time; outside of its reference period, the index is not further calculated.
I grafici a linea (in basso) riportano l'andamento nel tempo degli stessi indici bioclimatici.
Winkler's Index
The index reports the cumulative value of daily differences (deviations) between average temperatures (Tav) and the vegetation zero point (temperature above which vegetative activity resumes - 10 degrees). This index is calculated during the vegetative period of the vine until maturation and harvest: from April 1st to October 31st.
Serve a valutare quantitativamente la potenzialità ambientale del vigneto dal punto di vista dell'input termico della stagione in corso, input che è legato alle possibilità di accumulo degli zuccheri e alla maturazione delle bacche.
As reported in the specialized literature, the Winkler index informs about the suitability of the territory for the cultivation of a particular grape variety, as each variety requires a specific cumulative temperature to complete the vegetative cycle and reach maturity. Below is the table that relates the Winkler index to the varietal suitability of the vine. In literature, it is possible to find reference values of the index for additional varieties of interest in order to assess the potential of a specific agricultural lot with respect to a specific grape variety.
Normalized Winkler's Index
As reported in the specialized literature, the Winkler index informs about the suitability of the territory for the cultivation of a particular grape variety, as each variety requires a specific cumulative temperature to complete the vegetative cycle and reach maturity. Below is the table that relates the Winkler index to the varietal suitability of the vine. In literature, it is possible to find reference values of the index for additional varieties of interest in order to assess the potential of a specific agricultural lot with respect to a specific grape variety.
Ti = HuT, with T = average hourly temperatures, for 10°C<T≤35°C
Ti=0 for T values external to the interval 10°C- 35°C
Huglin's Index
The index reports the cumulative value of the sum of two daily deviations, calculated respectively between the following values: the daily average temperature (Tav) and the vegetation zero point (10 degrees); the daily maximum temperature (Tx) and the vegetation zero point.
The calculation approach and purpose/use of the index is similar to the Winkler index.
However, Huglin also takes into account the contribution of heat spikes on days with an average temperature below 10°C; in addition, a coefficient K is introduced that takes into account the latitude, that is, the different duration of daylight hours.
Tav=Daily average temperature, Tx=Daily max temperature K=latitude coeff. The index is calculated from April 1st to September 30.
Below is the table that relates the Huglin index to the varietal suitability of the vine. In literature, it is possible to find reference values of the index for additional varieties of interest in order to assess the potential of a specific agricultural lot with respect to a specific grape variety.
Fregoni's Index
The Fregoni index considers the day/night temperature fluctuations and the "cool" days, with temperatures dropping below 10°C, in the 30 days prior to harvest. In WiForAgri, it is calculated starting from September 1st.
The Fregoni index is used to evaluate the potential quality of grapes and wines based on local climatic conditions that can allow:
the development of some noble components such as aromas, polyphenols (anthocyanins and tannins), and non-oxidizing enzymes;
the maintenance of an adequate level of acidity that contributes to a high vine longevity.
For example, the Fregoni index helps to understand why it is difficult to obtain quality wines from early ripening grape varieties in hot or Mediterranean climates/areas: in such climates/areas, the 30 days prior to harvest (for early ripening varieties) generally correspond to the month of August, where it is not frequent, even at night, for the temperature to drop below 10°C.
Nh(T<10°) refers to the number of hours during the day/night with a temperature below 10°C.
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