Soil erosion in an avalanche release site (Valle d'Aosta: Italy): towards a winter factor for RUSLE in the Alps

Abstract

Abstract. Soil erosion in Alpine areas is mainly related to extreme topographic and weather conditions. Although different methods of assessing soil erosion exist, the knowledge of erosive forces of the snow cover needs more investigation in order to allow soil erosion modeling in areas where the snow lays on the ground for several months. This study aims to assess whether the RUSLE (Revised Universal Soil Loss Equation) empirical prediction model, which gives an estimation of water erosion in t ha yr −1 obtained from a combination of five factors (rainfall erosivity, soil erodibility, topography, soil cover, protection practices) can be applied to mountain areas by introducing a winter factor (W ), which should account for the soil erosion occurring in winter time by the snow cover. The W factor is calculated from the ratio of Ceasium-137 ( 137 Cs) to RUSLE erosion rates. Ceasium-137 is another possible way of assessing soil erosion rates in the field. In contrast to RUSLE, it not only provides waterinduced erosion but integrates all erosion agents involved. Thus, we hypothesize that in mountain areas the difference between the two approaches is related to the soil erosion by snow. In this study we compared 137 Cs-based measurement of soil redistribution and soil loss estimated with RUSLE in a mountain slope affected by avalanches, in order to assess the relative importance of winter erosion processes such as snow gliding and full-depth avalanches. Three subareas were considered: DS, avalanche defense structures, RA, release area, and TA, track area, characterized by different prevalent winter processes. The RUSLE estimates and the 137 Cs redistribution gave significantly different results. The resulting ranges of W evidenced relevant differences in the role of winter erosion in the considered subareas, and the application of an avalanche simulation model corroborated these findings. Thus, the higher rates obtained with the 137 Cs method confirmed the relevant role of winter soil erosion. Despite the limited sample size (11 points), the inclusion of a W factor in RUSLE seems promising for the improvement of soil erosion estimates in Alpine environments affected by snow movements.

Future Scenarios of Soil Erosion in the Alps under Climate Change and Land Cover Transformations Simulated with Automatic Machine Learning

“…We are also aware that snow-induced erosion might be relevant in some mountain areas and RUSLE-like models cannot describe this effect [58]. In D-RUSLE, the computation of R-factor includes the snow cover sheltering effect, thus simulating the snow accumulation and melting process, but our model neglects the erosion because of snow melting.…”

Monthly RUSLE soil erosion risk of Swiss grasslands

“…In contrast, for all winter months, a relatively low soil erosion by water risk (winter average 0.02 t ha −1 month −1 ) was predicted (Table 3, Figure 3, Main Map) because of low rainfall erosivity (due to snow fall/ snow cover). However, processes like snow gliding and avalanches or even snow melt are not included in the present model and need to be considered separately (Ceaglio, Meusburger, Freppaz, Zanini, & Alewell, 2012;Meusburger et al, 2014;Stanchi et al, 2014). The mean monthly soil loss due to water erosion for summer is 48 times higher than the mean soil loss in winter, 6 times higher than in spring and 3 times higher than in autumn (see Schmidt et al, 2018b).…”

Soil erosion by snow gliding – a first quantification attempt in a subalpine area in Switzerland

“…The NaI detector has the advantage of providing an integrated measurement over an area of 1 m 2 . The commonly observed, intrinsic small-scale variability (∼ 30 %) for 137 Cs (Sutherland, 1996;Kirchner, 2013) is thus smoothed. Nonetheless, around 10 % of the uncertainty of the 137 Csbased soil erosion values can be attributed to the variability of replicated measurements on each single plot.…”