Spatial and temporal variability of snow depth and ablation rates in a small mountain catchment

Abstract

Abstract. The spatio-temporal variability of the mountain snow cover determines the avalanche danger, snow water storage, permafrost distribution and the local distribution of fauna and flora. Using a new type of terrestrial laser scanner, which is particularly suited for measurements of snow covered surfaces, snow depth was monitored in a high alpine catchment during an ablation period. From these measurements snow water equivalents and ablation rates were calculated. This allowed us for the first time to obtain a high resolution (2.5 m cell size) picture of spatial variability of the snow cover and its temporal development. A very high variability of the snow cover with snow depths between 0-9 m at the end of the accumulation season was observed. This variability decreased during the ablation phase, while the dominant snow deposition features remained intact. The average daily ablation rate was between 15 mm/d snow water equivalent at the beginning of the ablation period and 30 mm/d at the end. The spatial variation of ablation rates increased during the ablation season and could not be explained in a simple manner by geographical or meteorological parameters, which suggests significant lateral energy fluxes contributing to observed melt. It is qualitatively shown that the effect of the lateral energy transport must increase as the fraction of snow free surfaces increases during the ablation period.

Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

“…Note that snow height determines most of the spatial variability in SWE since density typically does not have a pronounced spatial variability [6]. In the assessment of slope stability (avalanche danger), small scale spatial variability on the scale of <1 m is influential on avalanche release, as is (if such measurements are possible) layer thickness (mm scale) [30].…”

“…Similarly, SWE, HS, and HNS are vital parameters that need to be measured in areas of complex terrain, where wind-driven snow redistribution can significantly change snow height measurements, such that with a 1.5 m average snow depth, the point based HS measurement can typically vary by up to 5 m on a horizontal spatial variability of meters [6,21]. SWE is driven by precipitation, temperature, wind, and incoming/outgoing radiative fluxes.…”

“…For assessing spatial snow distribution on a scale of a few meters, an accuracy of 0.1 m is a useful benchmark [6], which would correspond to a range between 20 to 30 mm SWE for typical mean densities in alpine snow covers. Note that snow height determines most of the spatial variability in SWE since density typically does not have a pronounced spatial variability [6].…”

“…Snow and avalanche research institutes have recently started to intensively use LIDAR and TLS measurements for a variety of purposes from surface deformation in permafrost areas to pre/post storm snow height measurements for analyzing snow distribution patterns (see, e.g., [6,25,39,40]). …”

“…In the forecast of avalanche danger, particularly for wet snow avalanches, important decisions must be made based on these parameters describing the development of the snowpack and its variability with slope angle, aspect, and altitude [4,5]. In snow hydrology, if the spatial distribution of SWE and HS is measured over entire catchments, we can obtain an estimation of the total stored water resources [6,7]. This information is extremely valuable for hydroelectric companies, water supply companies, and risk assessment [8,9].…”