The majestic Himalaya draws its name from snow. “Himalaya” is descriptive term in Sanskrit which translates to “abode of snow”. However, snow cover area is decreasing in Himalaya as it is the world over. Global warming is further exacerbating the rate of decline — snow pack is sensitive to temperature change.

Snow, a major source of fresh water, governs interactions between atmospheric and land surface processes in high mountains. It is thus essential to local communities, and important to climate scientists. However, the understanding of snow cover dynamics in terms of space and time is limited across the Hindu Kush Himalaya (HKH), which is a climatically sensitive region.

What is most important in the context of the Himalaya is an understanding of spatial and temporal variability. Differences in weather systems (western and eastern Himalaya), and topographic control over snow climatology result in high spatial variability in snow cover distribution. It is important to comprehend this variability and the manifestations associated with it in developing appropriate region-specific adaptation measures.

Research carried out by the International Centre for Integrated Mountain Development (ICIMOD), “Climate and topographic controls on snow cover dynamics in the Hindu Kush Himalaya”, shows decrease in snow cover in study sites in Bhutan, China, India, Pakistan, and Nepal. Researchers used Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products from 2003 to 2012 to measure the inter- and intra- annual variabilities of four basins: Jhelum in India and Pakistan, Gandaki and Koshi in China and Nepal, and Manas in Bhutan and China. The four basins have been selected based on their locations to collect representative data from the western, central and eastern Himalaya. Statistical analysis was performed in order to shed light on the nexus between snow, temperature and downstream discharge.

Key findings from the research suggest that snow cover area in all basins except Jhelum is decreasing across the altitudinal range, and in all aspects. Research has found a distinct pattern in intra-annual snow cover variability reflecting two weather systems in action. The Jhelum Basin is influenced by the western disturbance in winter and the dominant snow system, and has a long melt period. The other three basins receive snow from the Indian summer monsoon, and have much shorter melt periods.

Snow cover is sensitive to temperature change. This correlation is strong at lower elevations, particularly below 6,000 metres, which is just about the snowline in the region. That snow melt is an important fraction of downstream discharge is an established fact, but contribution varies by elevation across seasons. An assessment of the correlation between snow cover upstream with downstream discharge in the Gandaki Basin indicates that melt contribution is from snow below an elevation of 5,000 metres in winter, and snow below 6,000 metres in spring.

Analyses of long term discharge in Gandaki, Koshi, and Manas indicate a decreasing trend which could be due to a decline in snow cover among many other things. The discharge is characterized by a high degree of variability during summer months. “This study adds to our knowledge of snow fall and melt dynamics in the HKH, and intra-annual snow melt contributions to downstream discharges,” said the lead author, Deo Raj Gurung, Remote Sensing Specialist at ICIMOD.

Decrease in snow cover area will have an adverse impact on downstream discharge in a snow dominant hydrological system. The strong association between temperature and snow cover indicates change in snow cover is in part induced by change in temperature. Thus the projected rise in temperature will likely reduce snow cover which will then translate into decrease in melt water which will in turn impact river hydrology.

The paper was prepared as part of the HIMALA Project at ICIMOD, which ran from 2010-2013 with a focus on studying climate impacts on snow, glaciers, and hydrology in the Hindu Kush Himalaya. It was funded by the United States Office for Foreign Disaster Assistance for International Development Office for Foreign Disaster Assistance (USAID/OFDA).The research was carried out by scientists within ICIMOD’s Cryosphere Initiative.

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