The report on the water situation in Piedmont in 2023 is online.
The document describes and analyzes the rainfall and snow data, the situation of the basins in terms of surface runoff and hydrological balance, as well as the underlying data of the main surface aquifers. From this year, the analysis of the water volumes available in 2023 in the Po basin, closed at the confluence with the Ticino in Ponte Becca (PV), stored in artificial reservoirs, in natural reservoirs and as a snow resource, is also introduced.
2023 was a year slightly below normal in terms of rainfall in Piedmont, with a overall deficit of around 9%. The rainfall that fell during the year in the part of the Po river basin, closed downstream from the confluence with the Ticino, was approximately 970 mm. However, the rainfall was not uniformly distributed over the region, in fact, if on the one hand the western basins end the year with a slight rainfall surplus, in the southern sector there is an average deficit over the year of up to 40%, while the plains and the northerners record smaller deficits.
In reference to the snowfall of the 2022-2023 winter and the beginning of the 2023-2024 winter season, the Piedmont Alpine arc has undergone a marked deficit of snow resources, both in terms of cumulative snowfall and thickness of snow on the ground, with the exception of the month of May 2023 which saw a decisive change of direction at the highest altitudes (>2500m), where snow accumulations exceeded the historical reference values for the month. The abundant snow resource at altitude at the end of spring guaranteed a date of complete melting of the snowpack at altitude, substantially on average, postponed by approximately 30-45 days compared to 2022.
In terms of meteorological drought, the year 2023 presented itself with two faces: if until April the scarce rainfall led the region to widespread conditions of moderate and severe drought, with even extreme peaks in the lower Asti and Cuneo areas, a very rainy month of May and an above-normal month of June brought back the situation everywhere beyond normal. On the 3-month scale, the rainfall surplus observed in July by the SPI and SPEI indices was well above the climatic norm over large portions of the Piedmontese territory (in particular in the Cuneo area). The general situation of normality, tending towards rain, continued until almost the end of the autumn season. The year 2023, however, ended with the months of November and December lacking in rainfall, so much so that almost the entire southern part of Piedmont once again found itself in conditions of moderate meteorological drought on all time scales ( 3, 6 and 12 months).
Overall, however, it was a substantially normal year, albeit with an uneven dry/wet alternation over the 12 months.
As found in the previous year, in 2023 negative deviations in scope were recorded compared to the historical reference values, mainly due to the presence of several dry periods during the year, with the exception of the abundant rainfall in May, but also deriving from the previous state of drought of the watercourses identified in 2022. This last aspect is confirmed by the fact that for some basins in the western sector of the region, such as Dora Riparia, Pellice, Malone, Dora Baltea, Varaita and Stura di Demonte, although total annual inflows higher than the historical average were recorded, the outflows were lower than the reference average, therefore resulting in negative deviations of scope. At the closing section of the Piedmont Po basin, the Isola S. Antonio (PV) section, the average annual flow rate was 40% lower than the historical average value.
In relation to the available water volumes (SWE, artificial reservoirs, Lake Maggiore) in 2023, positive deviations are observed, compared to the average availability over the assumed historical period, only in the August-October quarter, thanks to the high volumes stored in Lake Maggiore. In the other months of the year, the available water resource is lower than the historical average value, mainly due to the low snow supply (significant SWE deficit).
As regards groundwater, in 2023 the level of the surface water table, which has shown an almost ubiquitous decreasing trend since 2020, does not fall within the range of historical values except in the late spring-summer period and only in some areas in the plains of Novara, Biella and Vercelli, northern Turin and Cuneo on the right Stura di Demonte, therefore in 2023 the situation from the point of view of the availability of the resource was still critical.
