Joint mapping of statistical streamflow descriptors

Abstract

Summary An approach is presented for a joint mapping and regionalization of statistical descriptors of streamflow like the mean value and the coefficient of variation of daily data, the flow duration curve, moments and distributions of annual minima and maxima. Probability theory, and specifically extreme value theory, offers possible parametric relations to be tested, linking knowledge of the basic mean value and coefficient of variation with the other descriptors. This initial study is limited to theoretical results derived from the assumption that the original daily data follow the lognormal or the gamma distribution. With these standard distributions the statistical regularity found is surprisingly good when confronting the theory against the empirical data of daily streamflow from 35 catchments in the Moselle drainage basin in France. The lognormal distribution appears to be the best candidate for the flow duration curve, as well as maximum and minimum streamflow. The tail behaviour of streamflow maxima is well described, while for minima the results are more difficult to interpret. One problem might be the relative higher uncertainty in annual low flow data, and especially the sensitivity to outliers towards high values.