Uncertainties in Flow Duration Curves in anthropized catchments

Flow Duration Curves (FDC) are a traditional tool in water resources management. Their applications range from environmental protection planning to hydro-systems design. In many problems natural FDC are needed, that is curves referring to river regimes before alterations due to anthropic water uses.Estimation of FDC, as known, is uncertain in ungauged catchments. Also in gauged catchments, however, uncertainty may be relevant if available flow data are few or recorded after the anthropic alterations were set. This uncertainty may be high in mountain rivers, whose regime is typically more irregular and with significant alterations, mostly due to withdrawals for hydropower uses.The scope of this paper is to analyze these uncertainties, using a methodology to link anthropic uses to FDC alterations. Application to a catchment in the southwestern Alps is finally presented

Hydrological regime alteration and ecological flow evaluation in mountain rivers

In the Alpine region, the hydropower production has caused alterations in the hydrological regime of most rivers, due to the massive withdrawal of water and to the construction of dams and reservoirs, which modify the natural flow duration curve of the river. These alterations may result in a decrease in hydro-morphological and ecological quality of the river and limitations are considered, usually expressed as an ecological flow that has to be guaranteed. Many types of approaches are suggested in literature to define this flow, taking into account hydrological, physical, chemical and biological factors. Methods based only on hydraulic/hydrological parameters are often preferred, due to simplicity and robustness. More, with methods based only on hydrological parameters is simpler to take into account changes in river regime due to anthropic activities. However, some ecological issues are also important for river quality, such as the lentic-lotic characteristics of flow, but they are difficult to be expressed in crisp numerical values. In the last years more complex methods have been proposed as an alternative to hydrological models. One of them is the method CARAVAGGIO (Core Assessment of River hAbitat VAlue and hydro-morpholoGIcal cOndition). Although this model is able to take into account a great number of different aspects, its application is not always possible due to the difficulties in entering the river in some sites. In this paper a procedure able to merge the ease of use of hydrological methods and the multi-factor approach of CARAVAGGIO is proposed. Ecological flow is estimated from basic hydrological information, using a simple set of coefficients to take into account other quality issues, particularly the lentic-lotic features of flow regime. Application to a case study in the Province of Verbano-Cusio-Ossola, in the north-western part of Piedmont Region in Italy, is presented

Centenary (1930-2023) climate, and snow cover changes in the Western Alps of Italy. The Ossola valley

In this paper, we study centennial trends of climate and snow cover within the Ossola valley, in the Western Italian Alps. We pursue different tests (Mann Kendall MK, bulk, and sequential/progressive MKprog, Linear Regression, also with change point detection, and moving window average MW) on two datasets, namely (i) dataset1, daily temperature, precipitation, snow depth for 9 stations in the area, during 1930-2018, and (ii) dataset2, snow depth and density, measured twice a month (from February 1(st) to June 1(st)) for 47 stations during 2007-2023. We also verify correlation with glacier retreat nearby. In dataset1, we highlight a positive trend for minimum temperature with MK, and Linear Regression. Using MKprog/MW, a negative change of snow cover depth, and duration starting from the late 1980s is found. In dataset2, despite the annual variability in snow cover and 2022-2023 winter drought, we assess the maximum snow water equivalent (SWE) to be delayed with respect to maximum snow depth at high altitude (over a month above 2.700 m a.s.l.), highlighting the effect of settling in decreasing snow depth during spring. We also present a formula linking through Linear Regression the Day of the Year of SWE peak to altitude, relevant to assess the onset of thaw season. Due to the high altitude of the stations, and the paradigmatic nature of the Ossola Valley, hosting Toce River, a main contributor to the Lake Maggiore of Italy, our results are of interest, and can be used as a benchmark for the Italian Alps