In February 2021, the skies over much of Europe turned orange as the wind carried desert sand from the Sahara via Spain, France and Switzerland to Eastern Europe. To investigate the phenomenon and its consequences, Météo-France's Centre d'Études de la Neige, in cooperation with the Davos-based WSL Institute for Snow and Avalanche Research (SLF) and partners from Spain and Belgium, launched a citizen science project. This is where citizen volunteers actively support the work of researchers.
Just a day after the main event on 6 February, French institutes issued a call for help on social media. The appeal also went out in newspapers and on television and radio. The SLF took a different approach, selecting some of its many avalanche observers, spread out at different elevations and locations in the Swiss Alps. But the basic idea was the same: the volunteers were to collect samples of the Saharan dust contained in snow. Within just four weeks, 152 containers of red sand were ready and waiting in the laboratories, 32 of them from Switzerland. A total of 85 volunteers supported the initiative as citizen scientists. "As far as we know, this is the first time that such a large number of samples have been collected and analysed from a single dust event," says Martin Schneebeli, former head of the SLF's Snow and Atmosphere Research Unit and co-author of the study.
The researchers gained many new insights into the phenomenon, which are to be published in the coming weeks. Among other things, these will help to better understand the transport of matter in the atmosphere and how Saharan dust affects the duration of closed snow cover. For example, the researchers found that the mass and particle size of the dust deposited on snow surfaces decreased along the transport path from the Pyrenees to the Alps. They also confirmed the assumption that more dust was deposited on southern and southeastern slopes, which are exposed to the wind, than on north-facing ones.
"The results show that we can make scientific progress if we involve our fellow citizens in the data collection process," notes Schneebeli with satisfaction. For this to work, it is important to keep the work steps as simple as possible so as not to put would-be citizen scientists off. While some of the participants were experienced in snow measurement and so knew how to take samples, many were complete novices in this field.
Even so, they still provided some very useful material. What's more, the researchers involved describe the campaign as a "unique opportunity for informal exchange between scientists and the public". From their perspective, it was very stimulating to meet people who not only supported their research but were also curious about the work processes. "We will use our data to better understand the influence of Saharan dust on snowmelt and avalanche formation," says Schneebeli.