## 4 Discussion
The optimum temperature for phenolic accumulation is approximately 25 \({}^{\circ}\)C [20]. Therefore, both the positive and negative correlations (Figures 2 and 3) can be explained by the temperature differences between regions. Alentejo is characterized by GST higher than the other regions, which may explain the observed decrease of total phenols levels with temperature. However, the analysis of the impact of climatic variables on TPI is ambiguous since the impact of an environmental factor on each phenolic compound may be different. Our results showed that TPI can be reduced or increased depending on the region and precipitation period. It has been shown that the phenolic compound biosynthesis can be stimulated or inhibited depending on the type of phenolic compound, severity of water deficit and the period when the water deficit occurs [26]. On the other hand, the positive effect of water stress on phenolics concentration can be explained by the reduced berry size under water limitation [26]. Surface area/volume ratio of the berries increases with the decrease of berry size. Then, since phenolic compounds accumulate in the berry skin, smaller berries have a relatively greater solute to solvent ratio than larger berries [12]. Results showed that anthocyanins are negatively correlated with all monthly temperatures (TX, TG and TN) from June to August (Figures 2 and 3). Previous reports have shown that high temperatures negatively affect the content of anthocyanins at harvest due to an impairment of biosynthesis [21] and/or accelerated degradation [25]. For both varieties, the TN in July and August was the most influential variable in all regions. According to a previous study [30], for nocturnal temperature above and below 15 \({}^{\circ}\)C, grape berry anthocyanins are reduced and enhanced, respectively. The correlations between precipitation and anthocyanins (Figures 2 and 3) are different from one region to another. Specifically, a moderate positive correlation was found for Alentejo and a moderate negative correlation for Dao in April-June period (Aragonez). Enhanced water availability early in the growing season is beneficial, because it promotes vegetative growth and, consequently, berry development and its composition at later stages [29], thus explaining the positive correlation found in Alentejo. On the other hand, excessive moisture late in the growing season has been described to reduce anthocyanins content [30], though this effect is not clear in our results. The analysis of berry quality parameters at maturity across regions showed that the lowest levels of berry weight and TA occurred more frequently in warmer sites with low annual precipitation (Alentejo and Douro-D). Accordingly, in the cooler sites, with higher annual precipitation (Douro-C and Dao), berry weight and TA were higher (opposite effect observed with pH). The difference between warmer and cooler regions relative to berry weight, TA and pH was particularly well established. Moreover, berry weight and TA levels were more negatively affected in warmer than in the cooler years, while pH was more negatively affected in cooler than in warmer years (Figure 5). facilitate adaptation to warmer climates under plentiful water supply, such as in irrigated vines [54; 56]. However, for rainfed TON vineyards, the adaptation to warmer climates by evaporative cooling is limited. Moreover, TON may face early senescence of basal leaves and further leaf drop, with negative consequences for berry quality [53]. Therefore, isohydric varieties are more tolerant to drought/water stress than the anisohydric ones. Whether or not isohydric, some genotypes have different behaviour according to growing conditions (e.g., field versus greenhouse) and the degree of stress imposed on vines [57]. However, in this study, a comparison between varieties was carried out in the same regions and over the same growing conditions, using a plural number of genotypes and a wide range of plant age on each.