This paper presents the results quantifying the improved skill of the event SAC-SMA model over the event API models. The models were run for forty to fifty year periods without any adjustment of model parameters or states. The models were not adjusted in order to evaluate the model performance in the absence of forecaster skill. A simple base flow operation was added to the API model to generate a base flow during low flow periods. The first tests were performed for two headwater basins of the Des Moines River basin, Iowa. Two measures of error have been used to quantify the SAC-SMA improvements over the API model: hydrograph shape error was computed as a root mean square error of simulated hydrographs during flood events, and flood peak error was estimated as an difference between observed and predicted flood peaks. The comparison over more than 200 flood events found hydrograph shape accuracy improvements of 20% for low flood events and of 40% for high flood events, and peak error improvements of 23%. These tests will be extended over different river regimes and climate regions.
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