La Nina brings more cold but less snow to Himalayas

By Asha Ramachandran

White Christmas was, till a few decades ago, a major attraction in most hill resorts of North India, including Shimla and Mussoorie, when revelers would be greeted with a blanket of snow. This is now a rare sight. Late onset of snowfall and an early melt have not just limited tourist season to a shorter period but also spelt ecological issues, including lesser water availability and changing agro- patterns. Ironically, the maximum and minimum temperatures in the region have seen a decreasing trend over the years.

Shimla received its first snowfall of this season on January 8. Further north, Srinagar witnessed its first snowfall on January 4, though the higher reaches of the valley had intermittent snowfall since the day before. However, several parts of the Himalayan region received no snowfall, just rainfall as did the plains. Meanwhile, the entire northern India, including the Indo-Gangetic plains, reeled under a severe cold wave with winter having set in early in November.

The meteorological department has predicted an intensely cold winter but less precipitation in the form of rain and snow in the region. Climate scientists attribute this phenomenon to La Nina, which has developed for the second consecutive year and is expected to be in place till early this year. Temperatures are expected to plunge to around 3 degrees Celsius in the plains over the first two months this year as La Nina peaks.

The World Meteorological Organization (WMO) describes La Nina as a large-scale cooling of the ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall. La Nina’s effects on weather and climate are opposite to El Nino, which is the warm phase of the so-called El Nino- Southern Oscillation (ENSO).

In general, more snowfall is expected in a warmer atmosphere, as a result of more evaporation followed by more cloud formation. However, a recent study shows reduced snowfall over the western Himalaya in a warming climate. Icy-cold north-westerly winds from the Himalayas into the plains are what brings cold winters to the region. In the event of back-to-back western disturbances, the wind direction changes from cold north- westerlies to warm and humid easterlies, bringing rain and snow. However, meteorologists say, with La Nina in place, there would be less precipitation while cold winds bring down temperatures in the entire region, hovering close to freezing point. A cold wave is declared when the minimum temperature across the plains is around 4-6 degrees below normal, below 10 degrees Celsius and 0 degree in the hills.

Meanwhile, scientists have also attributed the extreme weather conditions to global warming, which is expected to trigger extreme ENSO events, which includes both La Nina and El Nino. In other words, rising global temperatures will warm the region between the Indian and Pacific Oceans faster than the central equatorial Pacific region, leading to conditions conducive to extreme La Nina events, most of which occur after an extreme El Nino. This fluctuation or swings of opposite extremes lead to the erratic weather being witnessed, including untimely rain and cyclonic storms.

Reduced snowfall and erratic rains across northern and northwest India have the potential of an adverse impact on ecology of the region, including water and agro-forestry. A study by the Indian Meteorological Department, using 20 years’ total winter precipitation and snowfall data of Himachal Pradesh during December to March, shows a decreasing tendency, the highest being for the month of January. The total precipitation and snowfall for different months were found to have decreased in the second decade under study by 6 to 36% and 16 to 86%, respectively.

The decadal analysis shows that the average date of ending of the snowfall season has advanced by two weeks in the second decade compared to the first decade. The analysis indicates a potential adverse impact on the river flow and agricultural as well as horticultural production in Himachal Pradesh and other states downstream.

A DRDO study on winter temperature and snowfall trends in north-west Himalaya showed a rising trend in average temperature in altitudes below 4,000 metres but a ecreasing trend in the average temperature in altitudes above 4,000 metres. Moreover, the study noted a significant decrease in snowfall in the lower altitudes. This decreasing snowfall trend is of concern in the region as it impacts the water availability, river flow and agro-forestry. Less snowfall, say scientists, would lead to less snow cover. It would also lead to less accumulation of snow, and subsequently ice, on the glaciers, which are an important source of water in the upper Himalayan reaches. Moreover, climate change has accelerated the melting of snow in the Himalayas in recent decades, creating unprecedented vulnerabilities that scientists have yet to fully understand.

Snow plays a significant role in water availability and in turn people’s livelihoods. In the Himalayan region alone, 129 million farmers depend on snow and glacier melt for irrigation. A deficit of snow also impacts water availability, ecosystems and hydropower generation. But the phenomenon known as snow drought, or relative reduction of the snow cover year on year, is still poorly studied.

In a paper published in 2020, researchers at the University of California monitored the intensity and duration of snow drought globally from 1980 to 2018. “The study underlines the importance of snow in supporting livelihoods for over 800 million people who depend on snow and ice melt,” said Aditi Mukherji, principal researcher at the International Water Management Institute (IWMI). “There’s already a lot of evidence that these glacier-dependent irrigation systems are facing challenges due to earlier snow melt, or seasonal changes in timing and volume of snow fall.”

Low snowfall in the Himalayan region has also led to an early green-up over the past decade. Agro-scientists have recorded an extended length of growth season, triggered mainly by a decreasing trend of snowfall in November and December. Rising temperatures in the lower altitudes and lesser availability of water has meant that crops, particularly fruit crops, are increasingly moving to higher altitudes, seriously impacting the livelihood of people. The inter-annual variation in grassland phenology under different climatic zones has also been shown to be linked to lower snowfall and late setting in of the season of growth due to lower temperatures. This is bound to impact the herders and grazers in their annual migration to grasslands.

Source: Himalayan News Chronicle