To most of us, the Himalayas is a snow clad, dry and cold mountain range. But trained eyes see through this apparent homogeneity and interpret the observed variations to understand the local climate and its implications. As a testimony to this, scientists from the Snow & Avalanche Study Establishment (SASE), Him Parisar, Chandigarh and the Divecha Center for Climate Change, Indian Institute of Science, Bangalore, have recently published a study on the variations in the 'whiteness of snow' across the Himalayas and its relationship with the mean winter air temperature and glacial stability.
When light falls on a surface, a percentage of it is absorbed and the rest is reflected. The proportion of the incident light or radiation that is reflected by a surface is called “albedo”. Thus, in crude terms, albedo signifies whiteness of a surface. Spatio-temporal variations in the albedo values of snow can exert significant impact on the formation and melting of snowpack. This variation is influenced by the physical characteristics of the top snow layer, air temperature, wetness, impurities, etc. Thus, studying the variations in the observed albedo of snow can help us infer about prevailing climatic conditions and associated behaviour of the snow cover.
The study led by Dr. H.S Negi of SASE assessed the temporal albedo variations of the North-Western Himalayan (NWH) snow in the last two decades (1991–2010) in comparison with the last 14 years (2000–2014). SASE has been monitoring Himalayan snow-cover with the help of snow-meteorological observatory network over north-west and central Himalaya for years. These scientists obtained the required snow albedo data from representative centers belonging to Lower Himalaya (LH), Great Himalaya (GH) and Karakoram Himalaya (KH) stations. The researchers also had access to satellite derived albedo data over these stations between 2001 and 2014. This long term albedo measurement study for winter snow over NWH is a first of its kind.
An important observation the study made was that the Himalayan snow cover and glaciers are more stable after the year 2000, as compared to the glacier retreat prior to 2000. “Several recent studies have reported a snow albedo increase in the recent decade only in the Karakoram region and suggested that snow albedo in lower and middle Himalaya was decreasing. But our study showed a decrease of snow albedo in the Greater Himalaya, stability in the Lower Himalaya, and insignificant increase in the Karakoram Himalaya, before 2000. Also, the study suggests that the snow cover is stable in the present decade,” says Mr. Vinay Kumar, a member of the study from the Divecha Center for Climate Change.
The winter mean air temperatures over western Himalayas were also found to be declining. This is in agreement with previous studies which reported a hiatus in winter average air temperature rise over the North Western Himalayas. “Our earlier analysis indicated an inverse relationship between snow albedo and mean air temperatures, especially in GH region. So the increasing trend may be attributed to the decline in winter average air temperature,”, explains Mr. Kumar.
The results of this study are not only useful in understanding the relationships that exist between snow albedo and other climatic factors, but also offers supportive evidences to many studies on the Himalayan climes. “Snow albedo is an important component in maintaining the Earth's energy balance and significant in understanding the snow cover characteristics. The data of snow albedo is also useful in Hydro-power and irrigation studies”, adds Mr. Kumar. He is optimistic that further investigations of similar kind will give more insights regarding the Himalayan climate.
About the Author(s): Dr. H. S. Negi, Dr. P. Datt, Dr. N. K. Thakur, Dr. A. Ganju, and Dr. V. K. Bhatia are scientists at SASE. Mr. G. Vinay Kumar was a PhD scholar at the Divecha Center for Climate Change during the course of study. Currently, he is employed as a scientist at NCAOR. Dr. H.S Negi can be reached at: <firstname.lastname@example.org>. Vinay Kumar can be reached at: <email@example.com>.
About the Research: This article is based on a research paper titled “Observed spatio-temporal changes of winter snow albedo over the north-west Himalaya” which appeared recently in the International Journal of Climatology; DOI: 10.1002/joc.4846.
This work was carried out under DRDO project ‘Him Parivartan’.