Results of the PCA analysis along with the time evolution of some disk parameters. Left panel: PCA for the parameters given in Table A.1. The two principal components, PC1 and PC2, result from lowering the dimension of the dataset. Some parameters are shown in color for a better visualization. Right panel: temporal evolution of the disk filling factor, its temperature, and temperature exponent. Best fits are also shown, with their parameters given in Table 4. Typical uncertainties are 0.03, 200 K, and 0.03 for F_d, T_d and a_T, respectively. They are shown for representative points to avoid data crowding.