Reservoir influences on droughts and floods characteristics in the Piedmont Region, Italy

Among the consequences of global climate change, the alteration of hydrological cycles is one of the most worrisome, since it can result in an intensification of the characteristics of extreme events. In the Anthropocene era, human activities can further increase the frequency and magnitude of floods and droughts. Therefore, it is of utmost importance to analyse the influence of anthropogenic activities on the magnitude and frequency of hydrologic extremes. In the present work, Piedmont region (Italy) was taken as a case study. The work analyses 15 pairs of regulated up- and downstream catchments characterized by the presence of dam/reservoirs (hydroelectrical, irrigation and small artificial reservoirs). Following an analysis of the climate and hydrological regime of the catchments, based on the collection and spatial processing of hydro-meteorological time-series, a main general purpose has been assigned to each catchment and information on the reservoirs present in the basins were collected. Then, extreme events occurring in the last decades were identified using the threshold level approach with a constant and variable threshold for droughts, and the peak over threshold method for floods. The characteristics of the extreme events, such as duration, deficit/volume and intensity/peak were then computed. The quantification of the impact of the different dam/reservoir purpose was analysed through the paired-catchment analysis, which consists in the comparison of the drought/flood characteristics between up- and downstream catchments. The obtained results seem to indicate an overall alleviation of the severity of the drought and flood metrics downstream. It was also noticed that the magnitude of these changes is related to the dam/reservoir purpose (higher for hydroelectric purpose) and their volume. This study could be used as a first estimate of human influence (reservoirs) on hydrological extremes in Piedmont.