USE AND MISUSE OF COMPLEX-MODELS - EXAMPLES FROM WATER DEMAND MANAGEMENT

The power of computers has increased in recent decades, and one might expect improved management to result because decisions can be made wit h understanding available only via models. However, there is potential for quite the opposite: poor decisions due to unrealistic model outpu t generated by users without access to appropriate training in the use of models. We discuss and, by reference to water demand models (IWR-M AIN, MWD-MAIN), illustrate three areas in which unintended errors of j udgment by untrained personnel may cause difficulty: Attributes of man agement models; if output from any type of model has no measure of con fidence, then results may be over- or undervalued. Input data; with co mplex models, problems here typically will be difficult to detect. Cal ibration and history-matching (verification); if these steps or data a re combined, then users should be less trustful of model output than o therwise. Because all models have weaknesses and because there always is uncertainty about output from any model, we end with suggestions fo r coping with complex models. Monitoring programs play a central role in such efforts because they can identify discrepancies between model predictions and actual events and because they can ensure time is avai lable to develop solutions for problems unanticipated in the modeling effort.