# Grapevine Phenology in Four Portuguese Wine Regions: Modeling and Predictions
## 4 Discussion and Conclusions  
The results of the GSM reveal a greater predictive capacity for flowering or veraison than for budburst. GSM presents an efficiency coefficient after cross-validation (EF*) above or equal to 0.5 for 20 varieties, 41 for flowering and 44 for veraison. Regarding the RMSEP, the SM performance for the three phenological stages is in general agreement with previous studies [26; 37; 38], with values below seven days. According to [PERSON] and [PERSON] [39], there is little information regarding the thermal requirement of the varieties. Besides, more valid information on table grape varieties is needed [40]. The objective was to fill the lack of information and determinate using the F parameter, the required thermal accumulation of each variety to complete each of the three phenological stages (Lisboa wine region). The varieties were classified into early, intermediate, and late according to the phenological stage. A study by [PERSON] et al. [41] allowed us to make some comparisons regarding the accumulation of the heat units of the varieties, where 34 varieties (19 white and 15 red) were selected, though only a few varieties were also used in the present study. For budburst, both studies agree that cv. _Avesso_, _Castelao_, and _Chardonmay_ are early varieties, while cv. _Viosinho_ is classified as intermediate. For flowering, both studies agree on the precocity of two red varieties and one white, namely cv. _Touriga Nacional_, _Touriga Franca_ and _Gouveio_, respectively. For the intermediate varieties, the suitability of cv. _Aragonez_, _Siria_, _Encruzado_ and _Antao Vaz_ varieties are verified as having a similar behavior in response to temperature. The latest variety in both classifications is also cv. _Moscatel de Setibul_, being more heat demanding. For veraison, the less demanding varieties with lower thermal accumulation are cv. _Touriga Franca_, _Jean_, _Tinta Barroca_, and _Alfrocheiro_. For this stage, the intermediate  
Figure 8: Ranking of the F measure for veraison by grapevine variety in the Lisboa wine region. Only models with EF \(\geq\) 0.5 are shown. varieties are also in agreement with the above-mentioned study in three red varieties, namely cv. _Baga, Vinhiao_, and _Tinto Cao_. The varieties with the highest accumulated heat units are cv. _Aritto_ and _Encruzado_. Another important feature is the ranking of varieties, which is in accordance with previous studies [42], highlighting that one given variety can shift from one quartile to the other for different phenological stages. Therefore, an early/late variety concerning a specific phenological stage can behave as a late/early variety for other phenological stages. The skill of the SM in the prediction of the grapevine phenological stages with relatively high performance highlights its potential to be used as a decision support tool for the winegrowers, assisting them in adopting the best practices for the optimization of grapevine yield and quality [43; 44; 45]. In this study, phenology data were used and combined with meteorological data collected at different weather stations installed in several main Portuguese wine regions, namely Douro, Vinhos Verdes, Dao, and Lisboa. Meteorological stations provide essential data for the adequate calibration of the phenological models, thus improving their predictive capacity [46]. Additionally, the sample size is a critical factor for the robustness and the validation of the phenological models. In the present study data set, a large number of varieties were taken into account, 36 of which were from the Lisboa wine region complemented by four from the Douro, five from the Dao, and six from Vinhos Verdes. A generalized model was developed for each phenological stage (budburst, flowering, and veraison) using centroid (averaged) parameters and showing quite satisfactory results. The performance of the models is in line with other studies carried out in the same area [31; 37; 47; 48; 49; 50; 51; 52; 53].