## 4 Discussion  
For the four selected vineyards (Alentejo, Dao, Douro-C and Douro-D), berry weight of TON (Touriga Nacional) and ARA (Aragonez) at maturity was negatively influenced by temperature, while strong positive correlations with precipitation (July to September) were found in Alentejo (TON) and Douro-C (ARA) (Figures 2 and 3). As vine water availability is closely related to temperature, an increase in temperature can lead to water deficit. Some studies have shown that when the vine is  
Figure 6: Cluster 2 – Cluster 1 differences in the mean TX (in \({}^{\circ}\)C) from 1 June to 31 August (dashed lines) for: (**a**) berry weight and total phenols index in Alentejo; (**b**) anthocyanins in Alentejo; (**c**) pH and potential alcohol in Alentejo; (**d**) titratable acidity in Dão; (**e**) potential alcohol in Douro-C. All parameters are for TON. The 11-day moving averages are also outlined (grey shaded areas). exposed to water stress, berry weight decreases [28; 48; 49], as water deficit generally leads to smaller berries, by inhibiting both cell division and cell expansion [12; 50]. For both grapevine varieties (TON and ARA), TA was negatively correlated with all monthly temperatures (TX, TG and TN) between June to August, while correlations with precipitation were generally positive but weak (Figures 2 and 3). Temperature enhances the respiration of tartaric and malic acids, thus leading to a drop in TA and increased pH [13; 14]. The observed positive influence of precipitation on TA levels at maturity for Dao and Douro-C is supported by previous studies [14; 17; 51]. However, the negative influence of precipitation in TA for Alentejo and Douro-D (Figures 2 and 3) was not originally expected and may be explained by the fact that these two vineyard sites are irrigated. However, future studies should focus on factors other than precipitation, such as atmospheric humidity and soil water holding capacity, since they also determine the vine water status [10]. The correlations between pH and monthly TX, TG and TN were generally positive, also in accordance with previous studies [14]. The associations between pH and precipitation variables were negative (more precipitation leads to lower pH), except for Alentejo and Douro-D (April to June), which is in accordance with the correlations with TA (Figures 2 and 3). The fact that the strength of the correlations between climate variables and pH is lower than between climate variables and TA (more evident for ARA) is possibly explained by previous results showing that pH is more affected by the canopy microclimate than TA [52]. Future studies with microclimate data may further clarify these correlations. The correlation analysis between climate variables and potential alcohol was dependent on the regions and varieties. In Alentejo and Douro-C (TON) and Dao (ARA), temperature had a strong positive influence on potential alcohol levels, despite the weak negative influences in Douro-D. Moreover, the strongest correlations were found between PA and monthly temperatures of June and July (fruit set/veraison period) (Figures 2 and 3). In agreement with previous reports, these results showed that total soluble solids (TSS, an equivalent measure to PA) accumulation was stimulated by high temperatures at veraison and a few days after [20; 21]. A strong negative correlation between PA and precipitation was only found in Dao for both varieties studied (rainfed vineyard), while a moderate positive correlation was found in Alentejo (irrigated vineyard) (Figures 2 and 3). As previously described, under irrigated conditions, TSS concentration can be decreased by unexpected precipitation due to the dilution effect caused by greater berry size [17]. Nonetheless, other reports have shown that the accumulation of sugar is improved in irrigated vines due to a stimulation of the photosynthetic activity [22] in semi-arid regions. Thus, based on previous studies, both positive and negative correlations between PA and precipitation may occur, depending on the specific site conditions.