Regionalization of Flow Duration Curves in Southern Italy

The Flow Duration Curve (“FDC”) is one the most effective and practical tools in hydrological sciences that not only enhances the understanding of the hydrological process of basins but also assists in analyzing water availability and stream flow fluctuations. The most significant challenge hydrologists have to face is an absence or scarcity of flow data in ungauged basins, where direct measurements are not feasible. To tackle this issue, regionalization of FDCs has emerged as a persuasive method. This approach, while applying available information in different basins, allows for reconstructing the hydrologic response in unmonitored basins.

This study focuses on the regionalization of FDCs in Southern Italy, containing 114 hydrological stations located in the Regions of Campania, Basilicata, Calabria, and Puglia, whose surface accounts for about 20% of the Italian country. For these areas, the only available authoritative information consists of archival reports of daily discharge and monthly rainfall and runoff over the period 1924 to 1994, characterized by gaps, repetitions, and ambiguities. Also, the complete river network and the outer boundary of the primary basins are available. No precise information is available for the location of the monitored sections.

For the first step (completed), historical data on daily discharge and monthly rainfall and runoff from 1924 to 1994 were digitized from archival paper reports collected by the National Hydrological Service (now expired) for 114 monitored sections, and their reliability was verified. For all the catchments, a hydrologically connected Digital Elevation Model was created integrating the authoritative Italian 20m × 20m DTM with the abovementioned physiographic information: this allowed for accurate reconstruction of physical, hydrological, topographic, and morphologic features in the GIS environment. The database was further refined with land use/land cover data from the CORINE initiative, with geological information coming from local maps, and with ancillary variables such as the baseflow index.

Currently, efforts are in progress to identify the main dependencies between flow variables and covariates in the database, to find common patterns and recursive behaviors. However, the data mining process is deeply intertwined with the choice of the regionalization methodology, which drives the main parameters and quantities to be investigated. Some issues that are being explored at present comprise (but are not limited to): i) understanding differences, similarities, and potential of annual FDCs and total FDCs (i.e. obtained by year-by-year or full-period records respectively); ii) investigation about relevant percentiles of FDCs representing low, high and semi-perennial flows; iii) normalization of FDCs; iv) cluster analysis also relying on Artificial Intelligence.

At a more mature stage, research will allow us to compare the results of different regionalization techniques, including parametric and non-parametric approaches, statistical methodologies, and quantile-based techniques. A comprehensive assessment of the relationship between hydrological and physiographic features will promote the construction of predictive models for streamflow behavior in unmonitored basins, fostering more efficient water resource planning and management in data-constrained locations.

Keywords: Regionalization, Flow Duration Curve, Digitalization, Geographic Information System (GIS), Southern Italy