Integration with uncertainty analysis workflow

Companion submethodology M09 (Peeters et al., 2016) discusses in detail the propagation of uncertainty through the numerical models in the BAs. The uncertainty analysis is carried out to provide an ensemble of the predicted maximum absolute and relative change and time to this change of each hydrological response variable at each model node.

To generate these ensembles, 3000 parameter combinations of the combined groundwater and surface water model are evaluated. For each hydrological response variable, only those parameter combinations for which the goodness of fit between observed annual hydrological response variables and their simulated equivalent meet a predefined threshold are accepted in the posterior ensemble of parameter combinations. In the case of Namoi, a pragmatic choice is made to set the acceptance threshold to the 90th percentile of goodness of fit for model evaluations. The ensemble of predictions for each hydrological response variable is thus based on the top 10% (i.e. 300) of parameter combinations for that hydrological response variable to allow robust estimates of the 5th, 50th and 95th percentiles of the prediction ensemble. Tests of this assumption suggest that this number is large enough to estimate the 5th, 50th and 95th percentiles robustly. The reasons for and implications of this assumption are discussed in Section

Except for the number of model replicates, in all other respects, the surface water modelling in the Namoi subregion follows the methodology set out in companion submethodology M06 (as listed in Table 1) for surface water modelling (Viney, 2016).

Last updated:
6 December 2018
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