Nonparametric procedures afford significant advantages over their parametric counterparts.
Nonparametric procedures generally reproduce the empirical structure of multivariate data sets yet they do not require assumptions about data or model structure, nor do they require parameter estimation. Therefore, nonparametric procedures do not suffer from the usual attendant losses associated with having chosen an incorrect model and used an inefficient parameter estimation algorithm. The challenges posed by extreme hydrological events continue to vex hydrologists. It is no longer adequate to base our understanding of extreme events on a single sample of streamflow. Naturally, improvements in our ability to predict extreme events will ultimately come from improvements in our understanding of the physical processes along with improvements in regional statistical methods.