Hydrologic models using water balance approaches typically use continuously observed streamflow data for calibration. Many large river basins in developing countries such as the upper Blue Nile River Basin of Ethiopia have discontinuous hydrographs that contain short continuous periods. Therefore, the efficient use of observed hydrographs for calibration of a hydrologic model is important to improve model performance. The goal of this study is to assess how limitations of continuity and duration in data affect hydrologic model calibration. A previously developed water balance model for the upper Blue Nile River basin was calibrated here using continuous and discontinuous (randomly sampled) data of different lengths. The performance of both methods was then compared each other in terms of parameter uncertainty and model efficiency. The results revealed that randomly sampled data require a shorter calibration length than continuous data to reach good model performance, about 36 and 120 months, respectively. This fact implies that discontinuous hydrographs can be useful in calibration. However, the number of high flow months included in the calibration data greatly affects model efficiency. This study suggests that randomly sampled calibration data should include at least 30% of high flow months of sufficient quality. The findings of this study will be essential to develop a hydrologic monitoring strategy for remote basins of the upper Blue Nile River basin and other similar basins where continuous observations are limited. Copyright © 2009 John Wiley & Sons, Ltd.