Deficit snowfall poses growing risk of glacial lake outburst in Himalayas, warn glaciologists

Shimla: The reduced snowfall in the Himalayas increases glacial lakes that pose a growing risk of lake outburst floods in the Himalayas, warn glaciologists.

They call for increasing preparedness, international cooperation and climate adaptation.

The Himalayan state of Himachal Pradesh received large deficit winter precipitation of 31 per cent since January 1 with nine out of 12 districts having received deficient precipitation, says the Meteorological Centre in Shimla.

The highest cumulative monthly rainfall in winter in Himachal Pradesh occurred in 1954, it says, adding the state received isolated rainfall in January with weak activity on many days and one day of normal activity on January 31.

In February, the state received five spells of precipitation with moderate precipitation at few places. Kullu and Mandi districts received normal rainfall with excess precipitation in Chamba district.

Meteorologists told IANS that warmer winters continued for the second consecutive year across India.

The cumulative countrywide rainfall from January 1 to February 29 is a large deficit by 33 per cent. The actual rainfall recorded during the winter season was 26.8 mm against the normal average of 39.8 mm.

According to meteorologists, increasing global warming has been altering the weather patterns, leading to anomalies in the temperatures and rainfall patterns.

The prime weather system, western disturbances, continued to dodge western Himalayas as they mostly travelled in the upper latitude.

Western disturbance is known to drive the weather activities and bring winters to northwest India and adjoining areas of central India. Both the intensity as well as frequency of western disturbances has been on the lower side this winter season.

Western disturbances are primarily disturbances originating in the west and travelling in the upper atmosphere in the subtropical westerly jet and arriving in the Indian sub-continent during the winter time. Their frequency peaks during December to February, with an average number of four to five per month.

Climate change and associated glacier recession have led to the formation of new glacial lakes and the expansion of existing ones across the Himalayas.

Many pose a potential glacial lake outburst flood threat, a climate change-induced threat, to downstream communities and infrastructure.

The term glacial lake outburst flood refers to the catastrophic release of a water reservoir that has formed at the site of a glacier.

Glaciologists warn of last year's Sikkim-like glacial lake outburst in other Himalayan states too.

According to a recent report on the Himalayas by the University of Zurich, glacial lakes are highly dynamic water reservoirs that respond to climate change by expanding in number, size and volume. This is particularly evident across the mountains of Asia, including in the Hindu Kush Karakoram Himalayas, Tien Shan and Tibet.

As a result of climate change, and consequent accelerated glacier recession, the number of glacial lakes in Hindu Kush Karakoram Himalayas increased from 4,549 lakes (398.9 square km) in 1990 to 4,950 lakes (455.3 square km) in 2015.

Several large-scale and regional assessment studies confirm the growth of glacial lakes and their hazardous potential across Asia.

Jammu and Kashmir has the highest combined exposure to potential glacial lake outburst flood with 556 lakes that include very high and high danger lakes.

This was followed by Arunachal Pradesh with 388 lakes, and Sikkim with 219 lakes. Sector-wise, Jammu and Kashmir face the greatest glacial lake outburst flood threat to roads and population, whereas the threat to cropland and hydropower is greatest in Arunachal Pradesh and Sikkim, respectively.

However, the highest-priority lakes, where urgent monitoring and local site investigations are recommended, include 13 lakes in Sikkim, five in Himachal Pradesh, four in Jammu and Kashmir, two in Uttarakhand and one in Arunachal Pradesh.

As glaciers melt, risks of catastrophic events -- landslides, sudden ice shears, and in some cases glacial lake outburst floods -- will rise.

Experts say the warming observed in recent decades has been accompanied by increased snow avalanche frequency in the western Indian Himalayas.

Powder snow avalanches tend to occur after intense snow precipitation during cold winter conditions, whereas wet and dense flows often coincide with warm spells, typically toward the end of the winter and early spring.

As a consequence, changing climatic conditions may modify avalanche activity. Land cover changes such as afforestation and deforestation are also likely to play a role.

According to the weather models, snow avalanche probabilities are highest if warmer temperatures persist during these months.

Extensive adaptation therefore needs to begin immediately to prepare for this future, even as mitigation to preserve glaciers as much as possible is also prioritised.