DNA Explainer: Why India's winter is colder, longer with more rains and less fog

As climate change takes centre stage, India, particularly the northern part is facing a colder, harsher and unusually longer winter spell. Delhi has shivered over the past week with the national capital recording the lowest temperature of the season and marking the coldest day in January on Tuesday in last nine years. 

This year saw one of the worst phases of heatwaves across north India and now it is facing a much colder winter season. This year there also has been unexpected rains causing a dip in the normal temperatures. India witnessed the seventh-most delayed monsoon retreat in 2021 since 1975.

Delhi lowest maximum and minimum temperatures

Delhi recorded a maximum temperature of 12.2 degree Celsius on Tuesday. This was the lowest in the last eight days. January 15 saw the lowest maximum temperature in 51 years, and the 10th coldest day by maximum temperature in the same period.

What's adding to the woes is that the lack of sunshine has made the cold harsher. Usually, for Delhi, January month marks biting cold but things start looking up around the middle of the month. However, this year things are different. 

North India has been shivering continuously for the last several days. Central India too is witnessing sharp gusts of cold wave. And there seems no reprieve from the cold as for now. The India Meteorological Department (IMD) has forecast that severe cold conditions will remain for the next two days.

Less foggy winter

This year the winter has been less foggy though, than normal, with fog visible only of late. There is bitter cold in North India including capital Delhi. The fog conditions in Delhi has been the lowest for December month since 1982. 

In January too, the national capital remained affected by fog for 252 hours against a normal of 292 hours. This is the lowest since 2008. IMD officials said the ongoing winter has recorded the lowest fog hours since 1991-92 over Delhi.

La Nina effect

Earlier forecast warned of an impending La Nina effect, leading to a major dip in temperature across North India with parts of it experiencing temperatures as low as three degree Celsius.

The warm phase of the east and the central Pacific Ocean, periodically seen once in two-seven years, is El Nino and the reverse process of cooling in the same area, is La Nina.

This phenomenon impacts the flow of trade winds, prevalent on either side of the equator. 

El Nino and La Nina are phases of a bigger weather pattern called ENSO or El Nino-Southern Oscillation in the Pacific Ocean with global weather ramifications. 

La Nina is expected to carry on with an 85% chance in December 2021-February 2022. It also means that La Nina event of 2020 continues to evolve and may last till early spring of 2022. 

It is uncommon to witness two El Nino events follow each other, back-to-back. But La Nina episodes are not unusual.

Statistically, of the 12 first-year La Nina events, six are followed by La Nina the next winter, four by neutral conditions and two by El Nino.