Low flow estimation in ungauged sites in Tuscany (Italy) using a regionalization by L-moments

Analyses of low flow characteristics are needed for several purposes in water resources planning and environmental management including determination of water demand and availability, river basin management, environmental flow availability definition. Low flow characteristics are estimated from observed streamflow data, identifying some duration curves and percentiles characteristics. For sites where data are not available, alternative techniques are necessary to infer this information. One of the more used is the regional regression approach that consists in using data from other catchments where stream flow data are recorded. After a thorough investigation of the dataset, the analysis of low flow indexes is carried out on the discharge data of 61 hydrometric stations located in Tuscany region, in Central Italy. The area is subdivided into different regions using the L-moments method applied to the 7- day annual minimum series. The division into subregions is tested using discordancy and heterogeneity statistics. A unique region and a subdivision into three different subregions, following previous studies on rainfall extreme values, are preliminary considered. The use of five subregions, starting from the previous subdivisions and taking into account some hydrological features, is also tested.