## 3 Results
### Relations on the Daily Timescale  
For the largest monthly temperature differences found between the clusters of the different quality parameters, daily temperature differences between clusters were calculated from June 1 to August 31. This analysis allowed for identifying critical days/periods that may have contributed to the interannual variability of maturation parameters. Therefore, daily maximum temperature differences between clusters were carried out for Alentejo (berry weight, pH, potential alcohol, TPI and anthocyanins), Dao (titratable acidity) and Douro-C (potential alcohol) samples of TON.  
The mean differences (cluster 2 minus cluster 1) in the daily TX between the two clusters of berry weight and TPI for Alentejo (from 1 June to 31 August) showed that TX in cluster 1 was generally lower than those of cluster 2, apart from a few exceptions (Figure 6a). Therefore, cluster 1 years (higher berry weight and TPI) were consistently cooler than cluster 2 years (lower berry weight and TPI). Moreover, cooler years were associated with higher anthocyanins levels (Figure 6b) and lower pH and potential alcohol levels (Figure 6c) in Alentejo. For titratable acidity in Dao, Figure 6d highlights that the years of cluster 1 (higher titratable acidity levels) had generally lower values of TX than those of cluster 2 (lower titratable acidity levels). Lastly, for the potential alcohol in Douro-C, Figure 6e shows that daily TX of cluster 1 years (higher potential alcohol) was generally higher than those of cluster 2 (lower potential alcohol).  
The aforementioned relationships on the daily time scale suggest some predictive potential. This should be, however, explored in greater detail in forthcoming studies, using more advanced and suitable statistical methodologies, such as the application of predictive regression analysis and low-pass filters to smooth out the high-frequency signals, but this is out of the scope of the present exploratory study.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Quality Parameter**} & \multicolumn{4}{c}{**Alentejo**} & \multicolumn{4}{c}{**Dão**} & \multicolumn{4}{c}{**Duro-C**} \\ \cline{2-10}  & **Jun** & **Jul** & **Aug** & **Jun** & **Jul** & **Aug** & **Jun** & **Jul** & **Aug** \\ \hline \multirow{3}{*}{Berry weight} & \(\Delta\)TX & \(-1.1\) * & & \(-1.2\) * & \(-1.4\) ** & \(-1.1\) * & \(-1.9\) ** & \(-1.6\) ** & \\  & \(\Delta\)TG & & & & \(-1.4\) ** & \(-0.9\) ** & \(-1.5\) ** & \(-1.3\) ** & \\  & \(\Delta\)TN & \(-1.0\) *** & & & & \(-1.2\) ** & & & \(-1.3\) ** & \\ \hline \multirow{3}{*}{Titratable acidity} & \(\Delta\)TX & & & \(-2.1\) ** & \(-1.3\) * & \(-1.2\) ** & & & \\  & \(\Delta\)TG & & & \(-1.3\) ** & & \(-1.0\) ** & & & \\  & \(\Delta\)TN & & & & & & \(-1.3\) ** & & & \\ \hline \multirow{3}{*}{pH} & \(\Delta\)TX & & & & & & \(1.5\) ** & & \\  & \(\Delta\)TG & & & & & & \(1.2\) ** & & \\  & \(\Delta\)TN & & & & & & \(1.5\) ** & & \\ \hline \multirow{3}{*}{Potential alcohol} & \(\Delta\)TX & & & & \(2.0\) ** & & & & \\  & \(\Delta\)TG & & & & \(1.5\) ** & & & & \\  & \(\Delta\)TN & & & & & \(0.9\) * & & & \\ \hline \multirow{3}{*}{Anthocyanins} & \(\Delta\)TX & \(-1.1\) ** & & & & & & & \\  & \(\Delta\)TG & \(-0.7\) ** & & & & & & & \\  & \(\Delta\)TN & & & & \(-0.8\) ** & & & & \\ \hline \multirow{3}{*}{TPI} & \(\Delta\)TX & & & & & & & & \\  & \(\Delta\)TG & & & & & & & & \\ \cline{1-1}  & \(\Delta\)TN & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Difference (in \({}^{\circ}\)C) between the clusters for monthly means of TX, TG and TN in June, July and August for ARA (cv. Aragone). * \(p\leq 0.05\), ** \(p\leq 0.01\), *** \(p\leq 0.001\). Only statistically significant differences are shown.