New Delhi: Expect less snowfall over the Himalayas, but intense cold wave in north India this winter, warn climate scientists.
The reason: The development of La Nina for the second consecutive year, which is expected to last through early 2022, influencing temperature and precipitation.
Climate scientists say that though there is no rulebook for La Nina’s behavioural patterns, the performance for winter rains is expected to be less than normal over north India, Western Himalayas is likely to see less snowfall than normal, winter temperature in the plains is expected to be less than normal, while the winter season is likely to be prolonged with more rain during the second half of northeast monsoon.
According to the World Meteorological Organization (WMO), La Nina refers to the 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.
It usually has the opposite effects on weather and climate as compared to El Nino, which is the warm phase of the so-called El Nino-Southern Oscillation (ENSO).
Winters made an early arrival in November this year, courtesy widespread snow and rainfall across northwest India.
Since then, as predicted, snowfall as well as winter rains have remained missing in action.
According to a report by Bloomberg, temperatures in India are expected to fall to as low as 3-degree Celsius in some northern areas in January and February before recovering, as the La Nina is likely to peak during that time.
Northwest India is now gearing up for a prolonged winter season ahead, along with some record low temperatures across the Indo-Gangetic plains.
“What brings cold to the region is the unabated north-westerly winds, which bring chilly winds from higher the latitude to the Indo-Gangetic plains. However, the passage of back-to-back western disturbances tend to change the wind direction from cold north-westerlies to warm and humid easterlies,” explained G.P. Sharma, President (Meteorology and Climate Change), Skymet Weather.
“However, with La Nina in place, we expect less amount of winter rains and thus icy cold winds would continue to blow over northwest India uninterruptedly, bringing down the temperatures.
“As we enter into the thick of winter season, we would see a series of cold waves engulfing both the hilly as well as plains of northwest India. Akin to La Nina season characteristics, minimum temperatures have already started plunging into the lower single digit, much below their average normal temperature. Meteorologists have predicted minimum temperatures are likely to close to freezing point in the coming days,” Sharma added.
Cold wave is declared when the minimum temperature across the plains settles below 10-degree Celsius and is 4-6 degrees below the normal average temperature. Meanwhile, the criterion for the hills is 0 degree.
Raghu Murtugudde, professor of Atmospheric and Oceanic Science and Earth System Science at the University of Maryland, currently a visiting professor at IIT Bombay, said, “La Nina has the potential to affect India’s winter as it influences the wind pattern and speed.”
According to scientists, global warming is expected to trigger more of extreme ENSO events that include both La Nina and El Nino. If global temperatures continue to rise unchecked, the climate of the Pacific is likely to undergo significant changes.
This means more occurrences of devastating weather events, and more frequent swings of opposite extremes from one year to the next, with profound socio-economic consequences.
For instance, less snowfall would result in less accumulation of snow over the glaciers. Also, in the absence of winter rains, spring melting season would begin before time, exposing glaciers to solar radiation quite early in the season.
“With rising temperatures, we can expect this cover to melt at a faster pace and it would be a prolonged one. This might give rise to some extreme weather events,” explained a scientist.
According to a report by Nature, global warming has increased the frequency of extreme El Nino that provides a favourable condition for extreme La Nina.
This occurs amid faster warming over the Maritime continent region (the region between the Indian and Pacific Oceans) than the central equatorial Pacific and increasing vertical temperature gradients that are conducive to extreme La Nina events.
The overall increased frequency in extreme La Nina events, most of which occur after an extreme El Nino, has important implications.
It means more occurrences of devastating weather events, and more frequent swings of opposite extremes from one year to the next, with profound socio-economic consequences.
India is already battling with substantial increase in extreme weather events, erratic monsoon patterns and much stronger cyclonic storms.
Usual traits of La Nina include reduced snowfall and winter rains across northwest India, which scientists believe would enhance stress on the Himalayas that are already dealing with rising temperatures.
“We know that warming is not going to reduce and whenever there is poor rainfall during the winter season, it would increase the stress on the Himalayan ecology. There would be enhanced climate effects on the vegetation. The situation would be quite troublesome, be it for agro-forestry, vegetation or fruit production etc. There is also a probability of glaciers retreating, but at what rate is uncertain,” said Jagdish Krishnaswamy, Dean, School of Environment and Sustainability, Indian Institute of Human Settlements, Delhi.
Argha Banerjee, Glaciologist, Earth and Climate Science, Indian Institute of Science Education and Research, Pune, added, “Majority of snow over the glaciers is brought by the monsoon season. Winter snowfall is very important as it provides snow cover to the glacial ice. Snow is the only source for nourishing the glaciers. It has been established that because of higher temperatures due to climate change and global warming, we see more rain than snow.
“If there is less snowfall, there will be less accumulation of snow over the glaciers. Also, in the absence of precipitation, spring melting season is also likely to begin early. Glaciers would be exposed to solar radiation quite early into the season, which tends to melt at a much faster rate on account of already high temperatures. And this melting season would also be a prolonged one.”
According to experts and scientists, the Himalayas are ecologically very fragile and with anthropogenic (human-led) factors, the region is quite vulnerable to natural disasters like flashfloods, landslides and torrential rains. Just like the one witnessed in Chamoli district of Uttarakhand in February 2020.
According to a research by Washington headquartered National Oceanic and Atmospheric Administration (NOAA), extreme El Nino and La Nina events may increase in frequency from about one every 20 years to one every 10 years by the end of the 21st century under aggressive greenhouse gas emission scenarios.
Michael McPhaden, a senior scientist with NOAA’s Pacific Marine Environmental Laboratory, said in the report that the strongest events may become even stronger than they are at present.
Less clear is the potential evolution of rainfall patterns in the mid-latitudes, but extremes may be more pronounced if strong El Ninos and La Ninas increase in frequency and amplitude.