Estimation of wine characteristics using a modified Heliothermal Index in Baden-Württemberg, SW Germany

The Heliothermal Index (HI) is one of the most common methods used to identify suitable areas for viticulture, using sums of air temperatures and latitude of locations. For this study, the HI and a modified version of it was applied to estimate annual wine characteristics in the federal state of Baden-Württemberg in southwest Germany. For this process, measurement data of 11 climate stations from 1960 to 2010 were used. In order to develop a method, 40 years of observation were selected and split into 30 years for developing an estimation method and 10 years for validation. The HI was modified by varying the time periods with which the index was calculated. Time periods with little effect on wine characteristics were identified and excluded to improve the estimation. The must density could be estimated with a bias of about 1 °Oe absolute value, which equals 0.21 °Brix, a mean average error (MAE) of about 4 °Oe / 0.82 °Brix and a root mean square error (RMSE) of about 5 °Oe / 1.03 ° Brix. The titratable acidity could be estimated with a bias of about 0.1 g/L absolute value, a MAE of about 0.7 g/L and a RMSE of about 0.9 g/L.