‘More than 80 per cent of sunlight falling on fresh snow is reflected back to space,’ explained one of the study’s co-authors, Tom Painter of the University of California at Los Angeles. ‘But sprinkle some dark particles on the snow and that number drops dramatically.’

While this effect has long been understood in theory and through modelling, the present study was the first to quantify the full effect of windblown dust on snowmelt rates. Using systematic measurements of dust-on-snow events, along with complementary climatic and hydrological data, the scientists demonstrated that run-off from the Colorado River basin had decreased by more than one billion cubic metres due to airborne dust. At Lee’s Ferry, Arizona, on the dividing line between the upper and lower Colorado River basins, the peak spring run-off occurs an average of three weeks earlier due to a recent five-fold increase in such dust.

‘Lake sediments in the mountains indicate that the increased dust load came after the vast increases in grazing and agriculture in the deserts of the southwest USA during the late 1800s,’ Painter said.

The scientists suggest that changing the way in which desert soils are managed could increase the amount of water available in the basin and improve the timing of its supply – shifting the peak time later in summer, when agricultural and other demands are greater.

November 2010