Warm winter: answer is blowing in the winds

The reduced frequency of western disturbances (WDs) — a weather system that brings icy, moisture-laden winds to northern India — was one of the key reasons behind the warmer and drier winter in 2015, a new research paper published in the journal Springer has said. Only eight WDs were observed in November-December 2014, as opposed to 16 observed during the same period in 2015. The El Niño weather phenomenon, which was severe in 2015, triggered some of the anomalies in wind patterns, weakening them, the paper added. The research paper is in line with the Indian Meteorological Department’s (IMD) analysis which said that December 2015 was the warmest on record.

The trend of weak WDs, the researchers indicated, has also been observed in 2016, thus affirming a trend of reducing rainfall and snow in key winter months. The research paper has been authored by Soumik Basu, Peter A. Bieniek and Akshay Deoras. Basu, a postdoctoral research fellow, and Bieniek, a research associate, both work at the International Arctic Research Centre, University of Alaska, Fairbanks (US), while Deoras is a Masters Student at Institute for Climate and Atmospheric Science, University of Leeds. 

The change in these weather systems led to lower winter rainfall, which in turn affected winter crops, the paper said. “We observed that these winds weakened and got shifted northwards of their normal position due to which even the western disturbances missed striking India. Higher temperatures in the mid-latitudes of the Eurasian region were also responsible for a decrease in western disturbances over India,” said Deoras.

Besides, below-par rainfall,“the absence of precipitation and WDs contributed to extremely high air pollution in New Delhi and also significantly degraded air quality in many cities of Northwestern India, leading to severe health issues”, the paper added. WDs are crucial for snowfall and rains in the upper reaches of the country. These low-pressure systems originate over the Mediterranean, Caspian and Black Seas and move eastwards across north and northwestern India, following the westerlies.

While comparing the average winter rainfall in November-December of 2014 and 2015, the researchers found that across eight states in the north and northwest, 31.4 mm of reduced rainfall was recorded in 2015. This was the weighted average taken over a period two months across Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Punjab, Haryana, Delhi and Rajasthan.