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Dust responsible for snowmelt in Western Himalayas

Date: 07 October 2020 Tags: Climate Change

Issue

Dust particles transported from as far as Saudi Arabia that gets deposited in the Western Himalayan Region — Hindu Kush, Karakoram, and western Himalaya ranges — has a large role to play in melting of snow.

 

Background

While black carbon has a large effect on snow darkening and resultant melting of snow, this is the first time the role of long-distance transported dust in elevating risk of snow melting in the Himalayas has been made.

 

Details

  • While dust transported as elevated aerosol layers get deposited at 1-5 km elevation, black carbon emission is mostly a surface phenomenon and influences melting of snow from surface to about 3 km elevation.

  • The relative impacts of dust and black carbon vary with surface elevation of snowpack. This is in addition to snowmelt caused by warming due to climate change.

  • Earlier studies have shown that the magnitude of snow mass decrease is about 1 mm per year at 1 km elevation, about 5 mm per year at 4.5 km elevation and about 3 mm per year at 6 km elevation.

  • Though black carbon has a larger snow albedo darkening effect than dust due to a larger mass absorption efficiency, the study found that the radiative effects of dust deposited on snow are comparable to black carbon in the Western Himalayan Region at higher elevations.

  • This is mainly because the deposition of dust by mass is 100-1,000 times more than black carbon.

  • Westerlies transport dust particles as elevated aerosol layers at maximum intensities mostly during the pre-monsoon period (March to May) and this gets deposited at higher elevations in the western Himalayan region.

  • Due to global warming, snow cover at lower elevations in the Himalayas will occur less frequently or totally disappear compared with snow cover at higher elevations.

  • The annual contribution of dust to snowmelt will therefore likely increase in the future as the black carbon effect at lower elevation weakens with dwindling snowpack.

  • Snowmelt is the main source of water for many major Himalayan rivers. Dust deposition during the pre-monsoon period causes early snowmelt water in the Himalayan rivers and a reduction of snowmelt water during peak summer month.

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