COVID pandemic reduced melting rate of Himalayan glaciers: Study

In a time when climate change is a major concern, a recent study offers a ray of hope for the Himalayan glaciers. The study, published in the journal Atmospheric Chemistry and Physics, suggests that reducing air pollution to levels seen during the COVID-19 lockdowns could significantly slow down the melting of these glaciers, which are vital for billions of people in Asia.

The COVID-19 pandemic in 2020 led to a significant decrease in industrial activities and transportation, resulting in cleaner air. This gave scientists a unique opportunity to study the effects of reduced air pollution on the environment, especially the Himalayan glaciers.

International researchers from India, Germany, and the UK analyzed data from this period. They found that less soot on the glaciers led to a decrease in snowmelt by 0.5 to 1.5 mm per day.

Himalayan meltwater crucial for Asia

The Hindu Kush Himalayan (HKH) mountains and the Tibetan Plateau are a massive snowy region, second only to the polar areas. This region, also called High Mountain Asia, is crucial for India and China because the meltwater from the Himalayas supports agriculture, hydropower, and the economies of these countries. About half of the annual freshwater for around 4 billion people in South and East Asia comes from the spring melt of the Himalayan snow.

Unfortunately, the Himalayan glaciers are melting fast due to climate change. In the last 30 years, there's been less snow, and it's melting quickly. This rapid melting is worrisome for the sustainability of the water supply and the loss of glaciers. Models predict that, in extreme situations, the Himalayan glaciers might vanish by the end of the 21st century.

The glaciers are getting thinner because of climate change, which affects temperature, precipitation, and the presence of light-absorbing particles like dust and black carbon. The darkening of snow caused by these particles significantly contributes to Himalayan snowmelt. Black carbon, especially, is very effective at melting snow. The increased emissions of greenhouse gases and black carbon in the densely populated southern Asian region have led to more snow darkening and melting.

The study found that the economic drop during the COVID-19 pandemic significantly reduced air pollution due to less travel and industry activities. This resulted in cleaner snow and less snowmelt, according to data from March to May 2020. The decrease in pollution influenced snow mass and runoff in the Himalayas and Tibetan plateau, thus preserving snow in these vital areas.

Team analyzed climate data with model

The research team used the ECHAM6-HAMMOZ chemistry-climate model with updated soot-snow parameterization for their analysis. This model was supplemented by data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based measurements from Aerosol Robotic Network (AERONET) stations in Pakistan and Tajikistan.

These comprehensive data sets helped the scientists understand the impact of reduced air pollution on the snow and atmospheric conditions in the region.

The findings are clear: reduced human-made air pollution leads to less soot on snow, which in turn reduces snowmelt. During the lockdown period, there was a 25 to 70 mm decrease in snowmelt compared to the 20-year average. This resulted in increased water storage due to reduced surface water runoff.

Dr Suvarna Fadnavis from the Indian Institute of Tropical Meteorology (IITM) reports, “The atmospheric opacity over this region decreased by around 10 per cent in April 2020 compared to before the pandemic. This is supported by measurements from MODIS, which also show a reduction in atmospheric opacity compared to the average of the last 20 years.”

Dr Bernd Heinold from TROPOS adds, “In the model, we were able to show that the decrease in air pollution reduced snowmelt in spring 2020 by 0.5 to 1.5 millimetres per day and thus reduced the runoff meltwater in the year by up to half.”

Prof. Ina Tegen from TROPOS emphasizes the importance of this discovery, saying, “Our results make it clear that of the two processes causing the retreat of the Himalayan glaciers – global climate change and local air pollution – a reduction in air pollution in particular could be a short-term help.”

Pollution cut lowered snow impurities

The researchers used a model to show that the lockdown led to cleaner air from March to May 2020, with a significant drop in aerosol levels. Both the model and satellite data (MODIS) confirmed a decrease in aerosol pollution during this period.

The study found a reduction in black carbon (BC) and sulfate concentrations, along with a decrease in dust levels. Ground-based measurements supported these findings, showing a substantial drop in BC over various regions. The decrease in aerosols also led to a decline in shortwave radiative forcing, resulting in lower atmospheric heating.

Importantly, the pollution reduction significantly lowered the concentration of BC in snow, reducing the snow-darkening effect caused by embedded aerosol impurities. The researchers noted some sporadic increases in BC concentration in specific areas, influenced by factors like changes in atmospheric circulation and snowmelt patterns.

The study explores the impacts of reduced air pollution on snowmelt, surface water runoff, and snow cover. The researchers found that the decrease in aerosol pollution led to a reduction in snowmelt and surface water runoff during spring 2020. This reduction was particularly pronounced in May over the Himalayas and the central Tibetan Plateau.

The decrease in snowmelt resulted in an increase in snow mass and snow cover fraction during spring 2020. The model's findings align with observations from MODIS, showing increased snow cover over certain regions. The researchers attributed these changes to a combination of reduced atmospheric heating and increased snowfall influenced by altered meteorological conditions.

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