Verification of snow-pillow measures through snow stratigraphy profiles for the determination of the Snow Water Equivalent in Valgrosina (northern Italy)

Snow plays a crucial role in the Alpine environment, since many diverse human activities, directly on indirectly, deeply rely on it. Estimating the Snow Water Equivalent (SWE) is particularly important to determine water resources available through snowmelt. The overall objective of this study is to estimate the spatial-temporal evolution of the Snow Water Equivalent in Valgrosina, a tributary valley of Valtellina, which is exploited for hydropower production by A2A S.p.A. Specific objectives include: i) the verification of snow density measures at two meteorological stations equipped with snow-pillow; ii) the correlation of snow density and snow height manual, discontinuous, point measures with morphological characteristics and continuous data; iii) the development of a procedure to derive spatial maps of SWE. During the winter season 2022-2023, four field campaigns were organized for measuring snow properties. The campaigned were carried out one per month, from December to March, to consider the evolution of the snow cover with the season. During each campaign, a snow stratigraphy profile was executed close to each of the two meteorological stations equipped with snow-pillow. Each profile was characterized in terms of snow height, temperature at 5-cm intervals, snow penetration resistance, snow density and number of layers. Each layer was described in terms of humidity, average grain size and form, and hardness (hand test). Comparisons between continuous station data and profiles were made to verify the similarity of density measures and relate possible inconsistencies to specific layer properties. Snow depth and snow density manual measures were performed at other locations in the valley, characterized by different elevation, slope and aspect in comparison to the stations and the complete profiles. An exploratory analysis was carried out to correlate continuous measures to point measures through morphometric variables. Preliminary results show a high spatial variability of snow height and a tendency of snow-pillow to underestimate snow density and SWE (between 37% and 55%) in comparison to profiles. This underestimation is variable according to snow layer thickness and hardness. For reliable correlations, a second group of campaigns will be carried out next winter, selecting measuring points a-priori based on morphometric characteristics. The possibility to introduce indirect spatial measures through geophysical instrumentation will be explored too.