HYDROLOGIC SIMILARITY OF RIVER BASINS THROUGH REGIME STABILITY

The seasonality of streamflow can vary widely from river to river and is influenced mostly by the local seasonal cycles of precipitation and evaporation demand, by the timing of snowmelt (if any), as well as by travel times of the groundwater component of runoff. Traditionally, streamflow regimes have been analyzed from a static point of view to produce classifications useful to a prior general understanding of the similarità and differences of different rivers across wide regions. Methods for systematic clas-sification have been proposed in the recent years but rarely quantitative values have been provided to characterise numerically specific features of the seasonal evolution of streamflows. The aim is twofold: (1) to select some quantitative indices able to objectively distinguish slightly or greatly different average seasonal streamflow pat-terns, and (2) to use some of the above indices to detect possible changes in the seasonality of streamflows over the last 30 years, which may be the result of a natural or anthropogenic non-stationarity. Indices used to investigate task (1) are essentially obtained through Fourier analysis, moments and the Informational Entropy Concept. Similar indices have bee