Desert dust melts mountain snow

Increasing dangers promote dust input and thus melt

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That almost everywhere in the world the glaciers are melting and the snow caps of Bergen are shrinking is nothing new. Now a study published in the "Geophysical Research Letters" shows a correlation between drought periods in the plains and an earlier snowmelt in the mountains. The reason for this is the dust carried by the wind into the mountains.

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Scientists at the University of Colorado, led by Tom Painter, have investigated the causes of snowmelt in the San Juan Mountains in southwest Colorado, which has started earlier and earlier. Located in the quadrangle between Colorado, New Mexico, Arizona and Utah, this region was one of the longest snow-capped mountain ranges in the American West back in the 1980s. In the meantime, however, snowmelt has advanced by about a month in several years.

Snowmelt always earlier

The scientists found that in the years with a particularly early snow melt several times larger amounts of dust from the approximately 300 kilometers distant deserts of Arizona and New Mexico had been registered in the mountain area. This "dust shower" always appeared when the already rather dry desert areas had been hit by a prolonged drought. The darker dust covered the white blanket of snow, lowering its albedo, the reflection of sunlight. This heated the snow stronger and melted earlier. Particularly striking was this process in 2006, in which the snow had been covered eight times by dust. As a result, it melted 35 days earlier than in relatively dust-free years.

"The relationship between dust and less reflection is already established, but the magnitude of the impact we measured and modeled in this system surprises us, " explains Painter. "The fact that dust can shorten the snow cover so strongly - for a full month at least - transforms our previous understanding of the susceptibility of the mountains to external influences." Ad

Global warming increases dust transport

"Recent studies suggest that as the climate changes, the southwestern US will become warmer and drier, " says Painter. "Increased dust deposition is therefore likely and thus a further shortened snow cover. This relationship will also change the water levels of the rivers and the soil moisture in the mountains, not only in the US, but also worldwide. "

For about one-sixth of the world's population, snowmelt is one of the most important sources of drinking water in spring, but it also provides valuable water for agriculture. However, continued global warming could make this resource more unreliable and significantly alter the amount and timing of the melt.

(University of Colorado at Boulder, 26.06.2007 - NPO)