*4.1. Evapotranspiration Calibration*

The calibration process worked with two temperature stations' data (0085A for Llobregat basin and 0353 for Ter basin, see Figure 2), where the required data for computing Penman ETP was available. Over the Llobregat's temperature stations, we applied a correction with the 0085A station dataset. Likewise, for Ter's upper-temperature stations. Correction obtained with 0353 station dataset was applied at the downstream Ter's sub-basins due to its geographic location. Figure 3 shows the results at both stations. The left-hand side graph displays the considered monthly evapotranspiration, and the right-hand side one, its cumulative distribution.

**Figure 3.** (**a**) Potential evapotranspiration calibration: Monthly ETP and (**b**) distribution of daily ETP at 0085A for the Llobregat basin; (**c**) Potential evapotranspiration calibration: Monthly ETP and (**d**) distribution of daily ETP at 0353 for the Ter basin.

To measure the efficiency of the correction, we computed the mean square error (MSE) for the Thornthwaite ETP, raw and corrected. Water volume contributions were checked for each season, and so, the ETP correction may change somewhat from one season to another.
