Regional flow-duration curves: reliability for ungauged basins

A flow-duration curve (FDC) illustrates the relationship between the frequency and magnitude of streamflow. Applications of FDC are of interest for many hydrological problems related to hydropower generation, river and reservoir sedimentation, water quality assessment, water-use assessment, water allocation and habitat suitability. This study addresses the problem of FDC estimation for ungauged river basins, assessing the effectiveness and reliability of several regional approaches. The study refers to a wide region of eastern central Italy and adopts a jack-knife cross-validation procedure to evaluate the uncertainty of regional FDC’s, comparing it with the uncertainty of empirical FDC’s constructed from short samples of streamflow data. The results (a) provide an evaluation of the reliability of the regional FDC’s for ungauged sites, (b) show that the reliability of the three best performing regional models are similar to one another, and (c) demonstrate that empirical FDC’s based on limited data samples generally provide a better fit of the long-term FDC’s than regional FDC’s.