Fire And Ice: Soot darkens Himalayan Glaciers

By Rishika Pardikar/thethirdpole.net

“We have vast grasslands in the area and during dry months like March and April, it is easy for fires to spread across the forest,” said Naveen Khandelwal, deputy director of the Pilibhit Tiger Reserve. He also noted that many farms surround the tiger reserve and, “when farmers burn crop residue, the fires sometimes spread to the forests also.”

The Pilibhit Tiger Reserve falls in the Terai Arc Landscape in the foothills of the Himalayas. It is one of the most fire-prone areas in the country.

According to a technical study by the Forest Survey of India, about 37.54% of the forest cover in Uttar Pradesh is either extremely highly or moderately fire-prone. The same study also notes that 32.75% of the forest cover in Uttarakhand which also falls within the Terai spread, is between extremely to moderately fire-prone.

In addition to being a local problem, fires in the Terai region have larger impacts, especially on glaciers in the Himalayas.

[Geographical representation of fires (image by: Siva Praveen Puppala, Senior Aerosol Scientist and Praveen K Singh, Ph.D. Fellow at Atmospheric Watch Initiative, ICIMOD)]

Forest fires and crop burning, in addition to pollution due to emissions from other sources like coal-burning power stations, transportation and brick kilns, are causing high soot depositions in the Himalayas.

Black carbon, a component in soot that absorbs light more strongly than any other substance in the atmosphere is now settling over Himalayan glaciers and disturbing the principle based on which these glaciers have survived over centuries, namely that light-coloured surfaces reflect sunlight and darker coloured ones absorb it.

“During April-May, about 30-40% of black carbon deposition in the [Himalayan] region is due to forest fires,” said Siva Praveen Puppala, Senior Aerosol Scientist at the International Centre for Integrated Mountain Development (ICIMOD), an intergovernmental research centre that works on issues critical to countries in the Hindu Kush Himalayas.

When black carbon particles settle over glaciers, they darken the surface and enable higher absorption of light and heat, eventually causing the snow or ice to melt. In addition to such direct impacts, black carbon particles that remain suspended in the atmosphere absorb sunlight and infrared radiation and warm the air which also contributes to glacial melt, among other impacts of warming like altered monsoon patterns.

P.S. Negi, a scientist at the Wadia Institute of Himalayan Geology, explained that vegetation burning – both forest fires in the summer between April-May and crop burning in winter between October-November – lead to high concentrations of black carbon in the Himalayan atmosphere.

Limited levels of crop burning are also noticed during the summer, Negi added.

The other factor to consider is that melting impacts by black carbon concentration can, at times, be compounded. Puppala explained that when black carbon depositions from the current period’s vegetation burning melt the top layer of a glacier, they bring to the fore black carbon concentrations in the layers beneath which had been deposited over the ice or snow in earlier periods, further adding to black carbon concentration and accelerating melting processes.

Links between fires, black carbon and glacial melt

Black carbon concentration over the Chirbasa site near the Gangotri glacier was highest during the month of May and lowest during August, noted a paper titled ‘Black carbon aerosols in the ambient air of Gangotri Glacier valley of north-western Himalaya in India’ published in August, 2019. Negi was one of the authors.

The paper noted that black carbon concentration in the region and its seasonal variability was significantly influenced by the emissions resulting from agricultural burning in the western half of the country and forest fires along Himalayan slopes during the summer.

Currently, Puppala and team are studying the impacts of black carbon on the Yala glacier in Nepal. The study shows that 23% of the annual black carbon concentration during 2016-17 drew its source from forest fires and agricultural burning, Puppala said.

He explained that during months like April significant amounts of black carbon are emitted into the atmosphere. This creates favourable conditions for higher glacial melt which is also influenced by other factors like cloud cover, temperatures being above zero degrees Celsius, radiation and precipitation. All these have a significant impact in determining glacial melt.

For Full Story, Click Here