Figure 3: Sensitivity indices for NPP based on (a) main effects using all inputs; (b) main effects using a reduced set of inputs; (c) interaction effects using all inputs; (d) interaction effects using a reduced set of inputs. The total effects (Sobol) index (TSI) is the addition of main effects and interaction index (TSI for all set of model inputs is computed as the summation of index values shown separately within insets (a) (main effects index) +(c) (interaction index), for a given parameter. Likewise, TSI for the reduced set of model inputs is the summation of indices shown within insets (b) (main effects index) +(d) (interaction index), for a given parameter, and TSI significance/importance is classified/ranked according to: TSI > 0.8 (very important), 0.5 < TSI < 0.8 (important), 0.3 < TSI < 0.5 (unimportant), and TSI < 0.3 irrelevant. 
