Two independent studies point to increasing risk from warming in the Himalayas that is accelerating snow melt and contributing to flooding in rivers. Last February, an avalanche and snow melt in the Chamoli district of Uttarakhand killed at least 70 persons and destroyed two hydropower projects.
The first study from researchers at the Vikram Sarabhai Space Centre and the University of Kerala used high-resolution, regional climate and chemistry models to quantify the effect of “snow darkening” from aerosols has on snow melt and flood risk, using data from 2011 to 2015.
Aerosols are particles suspended in the atmosphere and absorb sunlight. When some of these particles settle on snow, they tend to increase the amount of heat. Such aerosol pollution, the scientists say in their report, is “darkening” the Himalayan glaciers and snowpack, accelerating melt and increasing flood risks in the river basins near the Himalaya. The study appears in the peer-reviewed journal Water Resources Research.
Aerosol-induced snow darkening during spring and summer increases the temperature of the snow by 1.47°C and reduces the number of days of snow cover by 10 to 30 days.
The melt was also observed to be happening nearly 20 days earlier than normal and more visible over the Western Himalayas. This run-off, combined with the aerosol-forcing, increases the accumulated snow-melt by 41.3%. The frequency of occurrence of melt extremes doubled over the Himalayan region due to the aerosol-induced snow darkening effect
“The present study suggests that aerosol-induced snow albedo (the fraction of heat that is reflected back from the snow) has implications in perturbing the radiation balance, snow cover change and run-off over the Himalayan region. It has direct implications on water availability and security of South Asia,” the authors note.
Another study — by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital — shows that water vapour had a “positive radiative effect” at the top of the atmosphere (TOA), suggesting an increase in overall warming in the higher reaches of the Himalayas.
This precipitable water vapor (PWV), as it is known, is one of the most rapidly varying components in the atmosphere and is mainly accumulated in the lower troposphere that was about 10 watts per square metre (W m-2) at Nainital, which is at an altitude of 2200m; Central Himalaya) and 7.4 W m-2 at Hanle, Ladakh which is at an altitude of 4,500 metres.
The study, which appears in the Journal of Atmospheric Pollution Research, shows that the atmospheric radiative effect due to PWV is about 3-4 times higher compared to aerosols.
