This study addresses the estimation of flow-duration curves (FDC) in ungauged sites through the catchment classification. Forty-six catchments in the Upper Po river basin (Italy) were analyzed and classified through two different frameworks: the first scheme consists of the application of two clustering methods in a series considering six streamflow signatures, and the second one treats indexes of climate, physiography, soil, and land-use with the same clustering procedure. Catchments have been classified into three homogeneous groups: the first one is characterized by the lowest runoff and flash-flood events, the second one includes maximum runoff, and the third one shows intermediate behaviour. The estimation of FDCs was done using a lognormal distribution, whereas the regionalization was constructed applying a stepwise multiple linear regression, followed by a leave-one-out cross-validation. The results show great performance improvement when the regionalization model is found by taking account of the three different hydrological classes, with a mean absolute percentage error that decreases from 11% for the single region case to 7% in the three homogeneous regions case.

Abstract:A raster-based glacier sub-model was successfully introduced in the distributed hydrological model FEST-WB to simulate the water balance and surface runoff of large Alpine catchments. The glacier model is based on temperature-index approach for melt, on linear reservoir for melt water propagation into the ice and on mass balance for accumulation; the initialization of the volume of ice on the basin was based on a formulation depending on surface topography. The model was first tested on a sub-basin of the Rhone basin (Switzerland), which is for 62% glaciated; the calibration and validation were based on comparison between simulated and observed discharge from 1999 to 2008. The model proved to be suitable to simulate the typical discharge seasonality of a heavily glaciated basin. The performance of the model was also tested by simulating discharge in the whole Swiss Rhone basin, in which glaciers contribution is not negligible, in fact, in summer, about the 40% of the discharge is due to glacier melt. The model allowed to take into account the volume of water coming from glaciers melt and its simple structure is suitable for analysis of the effects of climate change on hydrological regime of high mountain basins, with available meteorological forcing from current RCM.

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This work has the objective to find and test methodologies for distributed hydrological model calibration starting from discharge measurements. As all distributed models, also FEST-WB demands a large amount of information and parameters. To reduce the calibration effort, in this study we assign a first initial distribution of values for each parameter starting from information about soil type and usage and we let calibration change only the mean value, through a correction factor. The study area in which this methodology has been applied is Piemonte, with a total of 50 flow measurements series. With this large amount of discharge data it is possible to test a multi-site calibration approach. The results show that the use of only one measure for calibration highlight some shortcomings in the validation results, while the use of all the measures together improve model performance in all catchments levels