NW India’s Unusual Rainfall and Western Disturbances in Early 2020

By: Staff Reporter
The capital of Delhi along with north-western plains of India witnessed heavy showers in the months of February and March 2020. These regions had also witnessed unusually cold months in November-December 2019. The anomaly comes further to light when the overall rainfall figures for the month of March 2020 is seen to be the highest on record. For the country as a whole, cumulative rainfall during this year's pre-monsoon season (up to March 11, 2020) was above long period average (LPA) by 82 per cent. For central India, it was above LPA by as much as 212 per cent (Table-1). This year’s frequent weather disturbances, as seen in February-March 2020 are in continuation of the record breaking chilly weather witnessed in December 2020. 
Weather n Climate

Why this unusual weather pattern?
The Indian Meteorological Department (IMD), in its press releases informed that intense Western Disturbances caused widespread rainfall/snowfall over the Western Himalayan region as well as squally thunderstorms over the adjoining plains of north-west India.
Western Disturbances are cyclonic storms associated with the mild-latitude subtropical westerly jet. These are low pressure areas travelling east from southern Europe, originating over the Mediterranean region due to a temperature difference between northern and southern latitudes. It enters India in the winter, bringing rain to north India and snow in the mountains. Western Disturbances itself are not an unusual climatic phenomenon, but what is unusual is its frequent occurrences from January to March 2020. There were 10 Western Disturbances in January 2020, nine in February and two till March 6, 2020. Usually, there are two to three Western Disturbances between January and February. Western disturbances are also known to bring calamities in the form of snowstorms and avalanches in the winter season.
Arctic Freeze connection
According to a report published in the Times of India, ‘the pattern of rapid succession of western disturbances hitting north India may be linked to unusual weather unfolding in the Arctic region.’ This winter the Arctic sea ice cover is at 10 year high which has enbled a strong polar vortex. The Polar vortex is a large area of low pressure, with an anti-clockwise flow of cold air surrounding the earth’s north and south poles. During winter, the Arctic polar vortex expands and pushes the cold air and western disturbances southward. It is because of this that the cold waves are experienced in the winter.
Arctic Ice growth
In the Arctic, December 2019 sea ice grew by an average of 82,100 square kilometres per day, which is faster than 1981 to 2010 average gain of 64,100 square kilometres.
Did you know?
The term Polar Vortex first appeared in an 1853 issue of E-Littlse’s Living Age– the Vortex referring to the counterclockwise flow of air.

Amit Bhattacharya, 2020. Pattern of frequent wet spells this season may be linked to record arctic freeze, Times of India Available at https://timesofindia.indiatimes.com/india/pattern-of-frequent-wet-spells-this-season-may-be-linked-to-record-arctic-freeze/articleshow/74502401.cms
Dimri, A P & Niyogi, Dev & Barros, Ana & Ridley, Jeff & Mohanty, U C & Yasunari, Tetsuzo & Sikka, D.. (2015). Western Disturbances: A Review. Reviews of Geophysics. 53. 10.1002/2014RG000460.
IMD, 2020. Available at https://mausam.imd.gov.in/backend/assets/press_release_pdf/extended8.pdf
National Snow and Ice Data Centre. That’s a wrap: A look back at 2019 and the past decade.
NOAA, 2019, the science behind the polar vortex. Available at noaa.gov/multimedia/infographic/science-behind-polar-vortex-you-might-want-to-put-on-sweater

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