COVID-19 Lockdowns Led to the Cleanest Snow Across Asia in 20 Years

COVID-19 Lockdowns Led to the Cleanest Snow Across Asia in 20 Years

When the COVID-19 pandemic led to shutdowns around the world, many regions reported the clearest skies in decades. In High Mountain Asia, another remarkable effect has been documented: much cleaner winter snow. A new study published in the Proceedings of the National Academy of Sciences found that during March to June last year, the concentration of polluting particles deposited on snow across a large swathe of the Himalayas was reduced by 30%. This has significant implications for water resources for the more than 300 million people who rely on the glacierized areas of the Indus River Basin for water.

Emissions of aerosols, such as dust and black carbon (soot), cause snow to melt faster and earlier in the season, disrupting historical runoff patterns that local populations have long relied on to sustain livelihoods. Aerosols have also been found to significantly affect the climate over India, Chandan Sarangi, an earth systems scientist from the Indian Institute of Technology, Madras, told GlacierHub. They absorb radiation from the Sun, affecting the energy and albedo (reflectiveness) of the Earth’s surface, and thus temperatures. The high mountains of Asia receive a mixture of pollutants during the summer months, including light-absorbing particles like dust and black carbon. “When deposited over snow and glaciers they can reduce the surface albedo a lot and affect the snowmelt and regional climate,” explains Sarangi.

Zhadang glacier darkening

Darkening on the surface of Zhadang glacier. Courtesy of Dr. Pengfei Chen.

The study took place over the Indus Basin, which covers parts of China, India and Pakistan. There are a lot of glacierized areas across the Indus, many found amongst its high altitude peaks. “It’s a very vulnerable basin for climate change because of the amount of glaciers and the number of people who depend on the water from glaciers and snow melt,” lead author Ned Bair, a snow researcher from the University of California, Santa Barbara, explained in an interview. “If you were to compare it with the United States it would be the equivalent of California, Oregon and Nevada.”

The north of India is a significant area for aerosol generation because of the large number of densely populated cities and its location upwind of the prevailing westerlies that carry dust during the spring and summer. During the pandemic, however, there have been widely documented improvements in air quality, for example in Delhi, notoriously known as one of the world’s most polluted cities. There was a strict lockdown across India in response to coronavirus between March and May last year. “Almost 50% of anthropogenic emissions stopped, causing a 20-30% reduction in air pollution over India,” said Sarangi, who lives in India. “Its significance was evident from the fact that our skies turned blue again and the Himalayan peaks were visible again from the lowlands during the lockdown,” he adds. The improvements seen during the shutdown were also momentous because poor air quality is a prevalent cause of mortality across India, and not only just in the densely populated cities, but in rural areas too.

The study used images from NASA’s MODIS satellites. By analyzing several different wavelengths of light reflected from the glacier surfaces, the researchers could quantify the concentration of light absorbing particles across the Indus basin, as well as snow-covered area and snow grain size. Bair explained that MODIS “is a great record, it has had over 100,000 orbits and is now at 20 years [of service], which is a long time for a satellite.”

The images taken by the MODIS satellites were of moderate resolution and so the research team had to account for this in their methods. Using a higher resolution satellite, such as Landsat, would have revealed finer details about the glacier surface, but Bair explained that the trade-off for MODIS’s moderate resolution is that you get daily observations of the whole Earth, allowing the team to trace changes day by day and identify the effects of individual snow or dust storms.

Bair went on to further explain some of the shortcomings within the research; that with MODIS they couldn’t tell the difference between the types of pollutants on the snow surface, only if the snowpack was polluted or not. This point is important because there are conflicting suggestions over the relative importance of dust, considered a natural pollutant from arid areas of the Middle East and Gobi Desert, and soot, considered an anthropogenic pollutant emitted by vehicles and burning, as sources of snow pollution in High Mountain Asia. Bair says that both dust and soot are a big concern, more so as there are things we have done on Earth that have created more dust, such as overgrazing and land use practices.

Despite Bair and his team being unable to definitively confirm the pandemic was the cause of the results, he said that “it is pretty unlikely the decreases [in snow pollution] were a natural phenomenon whereby there were fewer dust storms, and then all of sudden we have the cleanest snowpack in 20 years coinciding with observations of much cleaner air too.” The shutdowns associated with the pandemic are quite remarkable because “we don’t have experiments like this, when things just go on hold for a month or so in a lot of cities around the world,” adds Bair.

Polluted snow surfaces covered with dust and soot that absorb more solar radiation melt faster, and therefore have significant implications for the large human populations downstream that depend on the timing and quantity of meltwater each year. “By having a cleaner snowpack, you can actually mitigate some of the climate change impacts; the onset of melt will occur later and the snowpack won’t melt as quickly,” Bair explains. Shifts in the timing of meltwater during the spring and summer months are critical for managing water resources. Water stress pressures are worsening the challenges already facing High Mountain Asia communities and they may exacerbate resource-fueled geopolitical tensions. The results from this study perhaps offer some respite from the worsening water problems facing those of the Indus. And it shows that cleaner air is a tangible possibility for South Asia, rather than merely a dream or a hope.

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Agricultural activities pictured here in Sindh, Pakistan, a state which the Indus flows through before emptying into the Arabian Sea, relies heavily on seasonal river discharge from melting glaciers and snow high up in the Himalayas. Credit: Asian Development Bank.

Aerosol and deadly fine particle (PM2.5) pollution levels are back to being dangerous in the skies of Delhi recently, a change which Bair describes as not very encouraging, but not unexpected. Once the lockdowns were lifted, the effect of the pandemic proved to be fleeting. Bair believes it is unrealistic to think we are going to drastically change our behavior as a result of the positive impact we saw from the shutdowns, but “it’s encouraging that this research gets attention.” He also hinted that we are likely to see a lot more research into the effects of the pandemic.

These findings offer a unique insight into how glaciers could be protected from accelerated melting and preserve water resources if air pollution is reduced.





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