By analysing satellite images, researchers have gained insights into how snow cover varies in the mountains of upper Satluj basin1. Studies like this provide important clues to understanding the effect of climate change on the Himalayas.
A number of rivers in northern India, including Satluj (also called Sutlej), are fed by snow melts. At certain locations, more than half of the annual flow of Satluj comes from snow melting in higher elevations. The river supports a number of large hydropower projects, including the Bhakra Dam — the highest gravity dam in Asia, and is considered the lifeline of northern India. Hence, understanding snow cover variability is a critical part of managing water resources in the region. However, the tough climatic conditions make on-site experiments a logistical challenge. Hence, satellite iamges are used to study these regions.
Researchers from the Indian Institute of Technology Roorkee, used high resolution images captured by various NASA satellites to rebuild the tough Himalayan terrain on a computer screen. They studied the variation of snow cover area in a year, and how other parameters like elevation, slope and orientation of the slope face (or aspect) influenced snow cover.
Images taken over fourteen years (2001-2014) revealed interesting trends. They showed that snow begins to accumulate from September, peaks in March, and then begins to deplete to reach a minimum in August. In March, by the end of winter, a substantial part of the upper Satluj is covered in snow.
The study also showed that seasonal variation of snow happens mainly in regions that are neither too high nor too low. This is because, high altitude regions are always covered in snow, while lower altitudes, on an average, do not receive much snow. Only areas located between the height of 3900 m and 5100 m showed substantial seasonal changes in snow cover area. Though slope by itself doesn’t have a significant influence on snow cover, slopes facing north east and east showed the maximum snow-covered area.
Snow cover studies are important to understand the effect of a changing climate on the Himalayan mountains but the authors say it’s too early to come to conclusions. “We have only 15-20 years of data. We need to study the region for a few more years,” says co-researcher Mitthan Lal Kansal of IIT Roorkee.
Anil V Kulkarni from the Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru thinks that the annual variation of snow cover is more important than monthly variation. “Also, the paper doesn't calculate the amount of water stored in the snow covered regions, which is an important factor in mountain hydrology,” he adds.
