Abstract
Abstract. The input of mineral dust from arid regions impacts snow optical properties. The induced albedo reduction generally alters the melting dynamics of the snowpack, resulting in earlier snowmelt. In this paper, we evaluate the impact of dust depositions on the melting dynamics of snowpack at a high-elevation site (2160 m) in the European Alps (Torgnon, Aosta Valley, Italy) during three hydrological years (2013–2016). These years were characterized by several Saharan dust events that deposited significant amounts of mineral dust in the European Alps. We quantify the shortening of the snow season due to dust deposition by comparing observed snow depths and those simulated with the Crocus model accounting, or not, for the impact of impurities. The model was run and tested using meteorological data from an automated weather station. We propose the use of repeated digital images for tracking dust deposition and resurfacing in the snowpack. The good agreement between model prediction and digital images allowed us to propose the use of an RGB index (i.e. snow darkening index – SDI) for monitoring dust on snow using images from a digital camera. We also present a geochemical characterization of dust reaching the Alpine chain during spring in 2014. Elements found in dust were classified as a function of their origin and compared with Saharan sources. A strong enrichment in Fe was observed in snow containing Saharan dust. In our case study, the comparison between modelling results and observations showed that impurities deposited in snow anticipated the disappearance of snow up to 38 d a out of a total 7 months of typical snow duration. This happened for the season 2015–2016 that was characterized by a strong dust deposition event. During the other seasons considered here (2013–2014 and 2014–2015), the snow melt-out date was 18 and 11 d earlier, respectively. We conclude that the effect of the Saharan dust is expected to reduce snow cover duration through the snow-albedo feedback. This process is known to have a series of further hydrological and phenological feedback effects that should be characterized in future research.
Highlights
Mineral dust plays an important role in Earth’s climate and in biogeochemical cycles (Mahowald et al, 2010, 2013; Thornton et al, 2009)
The first three distributions can be due to the weak depositions that happened in February and March and were buried by new snow
We analysed the role of Saharan dust events on snowmelt in a high-elevation site of the European Alps
Summary
Mineral dust (hereafter referred as dust) plays an important role in Earth’s climate and in biogeochemical cycles (Mahowald et al, 2010, 2013; Thornton et al, 2009). The impact of dust on snow melting has been largely investigated in the western US, where both radiative and hydrological effects have been assessed using aerial, satellite, and automatic weather station (AWS) data (Painter et al, 2012a, b, 2013a, 2018; Reynolds et al, 2013; Skiles et al, 2012). In this area, the proximity of arid regions to the mountain ranges determines massive dust depositions on snowcovered mountain ranges. We present a geochemical characterization of dust reaching the Alps, and we discuss the possible biogeochemical and hydrological role of dust in the Alps
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