4.5.2. Varying the external factors
The alternative control options corresponding to seven different values of the aquaculture area are again considered. The system performance corresponding to each alternative over a time horizon of two years is evaluated under nine external conditions corresponding to all combinations of dry (D), normal (N), and wet (W) years. The aim is to figure out a control option which is optimal under the uncertainty affecting the external factors. The vector of criteria weights w2 is used in the AHP. For each external condition, the AHP scores associated with the different alternatives are reported in the rows of Table 2. In each row, the highest score is highlighted in bold. In order to select a reliable option, the mean score for each alternative is computed by averaging the entries along the corresponding column, as described in Section 3.2.6. By comparing the last row of Table 2 with Fig. 6 (solid line), it can be seen that, when robustness issues are taken into account by considering the variability of the external factors, the solution settles at low values of the aquaculture area, even though the economic criterion is favoured. This suggests that, on average, the expected economic growth related to increasing the aquaculture area (and thus the clam production) does not compensate the environmental losses.