Dealing with uncertainty in ecosystem model scenarios: Application of the single-model ensemble approach

Complex ecosystem models are often used as a means for gaining insight into ecosystem processes and as a management tool for resource managers. The uncertainty associated with these models present, however, a major stumbling block in their acceptance as a main stream management tool. Even if used, there is often a lack of confidence in the results and predictions due to the uncertainty. In addition, the difficulty in estimating model uncertainty and resulting error associated with simulation outcomes further limits model use. The lake ecosystem model DYRESM-CAEDYM (DYCD) includes hundreds of parameters and processes and inherently incorporates a large degree of uncertainty associated with model results. DYCD has been applied extensively to Lake Kinneret in recent years in various forms including as a means for examining long term management strategies. In this study, we test the reliability of the model as a management tool, given the large degree of parameter uncertainty. We do so by applying a singlemodel ensemble approach. Based on a sensitivity analysis (SA) previously conducted on the Lake Kinneret application of the model we introduced parameter uncertainty into the model response to a series of management scenarios. We do so in an attempt to test the underlying assumption that the trends predicted by the model, in response to the scenarios, are consistent across the range of uncertainty. The results of all the simulations, for each scenario, were combined to provide an ensemble of results for a series of state variables. Based on the variation in scenario results we estimated the consequences of parameter uncertainty for lake resource management.