Accuracy in flow regime alteration analysis

The frequency of hydrologic events has been recognized as a key factor affecting river ecosystem structure and evolution. Since a decade, the Range of Variability Approach (RVA) was the most widespread method for the frequency analysis of ecologically relevant hydrologic variables. Recently, a Histogram Matching Approach (HMA) has been proposed, based on a similarity measure of pre- and post-impact histograms for each variable. The accuracy of such methods has not been extensively evaluated. In this paper, the RVA and HMA are used to quantify the hydrologic alteration of a river subsequent to different scenarios of water diversion. Few inaccuracies are highlighted for both approaches. The necessity to develop a new method is discussed, whose main characteristics should be: a more accurate comparison of frequency distributions in different hydrologic conditions and the facility to consider the full range of values of each hydrologic variable. Current studies are focused on this issue.