Warmer winters increasing risk of avalanches in the Himalayas, studies find

Winters in the Himalayas are getting warmer, which is increasing the risk of avalanches, two new studies suggest.

The Himalayas, a massive 2,500-kilometre (1,553-mile) arc-shaped stretch of lofty mountains straddling Pakistan, China, India, Nepal, and Bhutan, are home to the largest concentration of glaciers outside of the poles.

So far, monitoring the trends and effects of changing climate in the Himalayas has been challenging because of the high altitudes and rugged terrain. Now, with the help of mountain-top observatories, Harendra Singh Negi of the Snow and Avalanche Study Establishment (SASE) in Chandigarh, India, and his team have analysed trends in winter (November-April) temperature and precipitation in the northwestern Himalayas and Karakoram from 1991 to 2015. Over this 25-year period, winters in the northwestern Himalayas have become warmer and wetter with less snowfall, the researchers report in a study published in Current Science.

This warming has increased the risk of wet avalanches in the western Indian Himalayas, a team of Swiss researchers who are examining tree-ring growth abnormalities, report in the Proceedings of the National Academy of Sciences.

Warmer and wetter winters

To find out how temperatures have been changing in the Himalayas, Negi’s team collected data from “a network of observatories” established by SASE on mountain-tops ranging between 2,000 to 6,000 metres (6,562 to 19,685 feet). Compared with other studies that use indirect satellite-driven data or models, these observatories, Negi said, contain “precious data” that “reflect the true picture” of climate conditions on mountain tops rather than at valley stations.

Even within the Himalayas, the climate varies according to the altitude of the mountains, so they divided the region into zones with similar elevations. The Lower Himalayas, with observatories at mostly 2,000 to 3,000 meters (6,562 to 9,842 feet),  are characterized by moderate temperatures and high rainfall. The Greater Himalayas, with observatories at 3,000 to 4,000 meters (9,942 to 13,123 feet), are colder with dry snowfall. The Karakoram region, with observatories at 4,000 to 6,000 meters (13,123 to 19,685 feet), is further up north where it is frigid and largely blanketed with swathes of glaciers. The Karakoram mountain range — which harbors the world’s second highest peak, K2, and the second longest non-polar glacier, Siachen — spans the borders of Pakistan (Gilgit-Baltistan), India (Ladakh), and China (Xingjiang Autonomous region).

Negi and his team found that overall, in the northwestern Himalayas, average temperatures rose by 0.65 degrees Celsius since 1991. This is “much higher than the global average” increase of 0.40 degrees Celsius during the same period, said Anil Kulkarni, a scientist from the Divecha Center for Climate Change at the Indian Institute of Science, India, which published a policy brief on the state of Himalayan glaciers and future projections. While the Greater Himalayan region saw the highest rise in average temperature of 0.87 degrees Celsius, Karakoram came second with an average increase of 0.56 degrees Celsius.

Walter Immerzeel, a glacier hydrologist at Utrecht University in the Netherlands, said that the warming trend agrees with other studies including his own. But he cautioned that summer temperatures also need to be considered, adding that “very limited information is given about the stations, data quality and sensors used” in this study.

From 2000 onwards, however, the Lower Himalayas experienced an unusual cooling in minimum and maximum temperatures, according to the SASE research. The reasons are unclear, Negi said, but according to past studies, the drop in minimum temperatures might be due to “large scale deforestation and soil degradation” whereas the cooling in maximum temperatures could be because of higher aerosol emissions reducing incoming solar radiation. This shift in the trend warrants further investigation, Negi added.

Although total precipitation has increased over the 25-year study period, a greater part of the precipitation has been falling as rain and lesser in the form of snow. Citing a study from the National Centre for Atmospheric Research in the U.S., on changes in precipitation with climate change, Negi explained that “with every degree rise in temperature, the moisture holding capacity of air increases by almost 7 percent which results in more precipitation, predominantly in form of rain than snow, since higher temperature hinders the formations of snow crystals.”

But “the effect of increasing precipitation or temperature is not straightforward,” said Mohd. Farooq Azam, a hydro-glaciologist at the Indian Institute of Technology in Indore, India. Winter temperatures at glacial altitudes, he explained, “are always much below zero degree and an increase by half degree or one degree doesn’t change the conditions of precipitation from snow to rain.”

Over the last few decades, “temperatures are surely increasing in the Himalayas, while most studies suggest decrease in precipitation, with few exceptions of increasing trends,” Azam said. “However a short time period or specific season (winter or summer) may have different results.”

The SASE researchers noted decreasing precipitation in the Greater Himalayas and Karakoram from 2000 onwards. Again, the reasons are unknown, said Negi, pointing out that there are many studies reporting a hiatus in global warming after 2000. He cautioned that this needs to be validated with data on glacial and vegetation cover, for example.

More rainfall can lead to a greater frequency of landslides and avalanches during late winter, warn the authors.

Greater risk of avalanches

A team of researchers from Switzerland examining tree-rings found just that: high avalanche activity in the Himalayas over the past few decades.

“Trees are eyewitnesses of past environmental changes,” said Juan Antonio Ballesteros-Cánovas, a researcher at the Institute for Environmental Sciences at the University of Geneva in Switzerland and lead author of the study. When snow gushes downhill, it is often the trees that bear the brunt of the impact. The damages are manifested as scars, loss of branches and tilting of stems. These are registered in the tree-ring records, explained Ballesteros-Cánovas.

By studying abnormalities in the rings of 144 trees on a slope between the villages of Solang and Dhundi in the Kullu district of Himachal Pradesh in north India, the researchers were able to reconstruct a record of avalanches that occurred as far back as 150 years ago. This slope affects the road that provides access to the newly completed and “strategically important” Rohtang tunnel that will enable year-round connectivity to Ladakh in the neighboring northern state of Jammu and Kashmir.

Almost no avalanches occurred in the region from 1940 to 1960, but high avalanche activity was recorded between 1970 to 1977 and 1989 to 2003 with more than 0.87 avalanches per year, on an average.

Using statistical modeling, the researchers linked increased air temperatures in late winter and early spring to a higher probability of avalanches. The authors stress that “the transformation of dry snow packs into wet snow packs is decisive for the release of snow avalanches in the region.”

Specifically, the “rise in liquid water content of the snowpack”, said Ballesteros-Cánovas, makes it “unstable and thus prone to trigger wet snow avalanches.” Also, moving snow with more water has less friction so it slides downhill easily, which can increase the distance traveled by the snow, known as run-out distances.

According to glacier hydrologist Immerzeel, this is “an excellent study on a very important topic” and one of the first to quantify an “increase in avalanching.”

“On the one hand, warming leads to less snow. On the other hand, it increases the risk of wet avalanches, which have a greater run-out distance,” he said.

The team highlighted the need for immediate measures to prevent blocking of roads in an area with rising traffic. Structures such as dikes and galleries can be installed based on the impact pressures, which could be determined using the tree-ring records, added Ballesteros-Cánovas.

Citations:

Ballesteros-Cánovas, J. A., Trappmann, D., Madrigal-González, J., Eckert, N., & Stoffel, M. (2018). Climate warming enhances snow avalanche risk in the Western Himalayas. Proceedings of the National Academy of Sciences, 115(13), 3410-3415.

Kulkarni, A., Shashikantha, P., Chaturvedi, R., Kulkarni, A. V., & Satheesh, S.K. (2018). State of Himalayan glaciers and future projections. Retrieved from this page.

Negi, H. S., Kanda, N., Shekhar, M., Ganju, A. (2018). Recent wintertime climatic variability over the North West Himalayan cryosphere. Current Science, 114(4). doi: 10.18520/cs/v114/i04/760-770.

This story was first published on April 24, 2018, by Mongabay-India.