Shifting winters? IMD records show warmer December, colder January

The winter chill has reached Delhi and its surrounding areas late for the last few seasons, even as January has become colder than usual, showed the data.

Winters in north-west India have become shorter and more intense in the past decade, with Delhi clocking fewer cold wave spells and cold days in December, but several more in January, showed data from the India Meteorological Department (IMD), setting off concerns among weather experts that the trend may be an effect of the climate crisis.

The number of cold wave days has also been on the wane over the past few years. Delhi had only two cold days last December. (Sanchit Khanna/HT Photo)

The winter chill has reached Delhi and its surrounding areas late for the last few seasons, even as January has become colder than usual, showed the data.

According to the IMD calendar, winter onset is marked over north-west India from mid-November till February. Scientists said an average winter season is supposed to intensify over these parts from mid-December.

The Indian weather office uses two categories to classify sharp drops in temperature – a cold day and a cold wave. The first is a condition when the minimum temperature is below 10°C and the maximum is at least 4.5°C below normal. The second is when either the minimum temperature over a region falls below 4 degrees Celsius (°C) or is 4.5°C below normal. Further, a “cold wave day” is a 24-hour period when the daily temperature falls under the parameters of a cold wave spell.

According to the weather department’s numbers, December last year was unusually warm, with no cold wave spells in Delhi all month, the first time this happened after 2017. In comparison, the Capital clocked four cold wave days in December 2021 and seven in 2020.

The number of cold wave days has also been on the wane over the past few years. Delhi had only two cold days last December. In 2021, the city recorded only one cold day and in 2020, it recorded two cold days. Records show that between 1990 and 2010, Delhi recorded between eight and nine cold wave days and 12-15 cold days on average every December.

However, in recent years, following a relatively warmer December, temperatures see a drastic fall come January, data shows.

Delhi recorded eight cold days this January, the most in the month in the last 15 years and the second-highest in records going back to 1992, according to IMD. Delhi also saw its longest cold wave spell in a decade this January — a five-day stretch from January 5 to January 9.

This is not the first time in the last five years that extreme temperatures were recorded in January in the city. On January 1, 2021, the Capital recorded a minimum temperature of 1.1°C — the lowest for Delhi’s base station in 14 years.

To be sure, according to IMD, January is considered the most intense winter month of the year, but scientists agreed that till a decade ago, the winter season was more evenly spread out between the end of November and January, than it is now.

Government weather forecasters said that several local and global factors are at play behind this trend of shorter and warmer winters over the region, stressing that these changes cannot be directly linked with the climate crisis, they said.

“Attributing warmer winters to the climate crisis based only on observations of one or two years will be premature. A lot of factors play a part in ascertaining temperature recordings during winter, and you will observe inter-decadal or bi-annual variability in the way temperature recordings behave,” said Soma Sen, an IMD scientist.

“This time, we saw a prolonged period without any western disturbance, which plays a primary role in ascertaining the intensity of winter,” Sen added.

However, Mahesh Palawat, vice-president (meteorology and climate change) at Skymet Weather Services, said the larger role of the climate crisis in north-west India cannot be overlooked. He said the onset of winter over this region is not only getting later and seeing an intense spike for a few weeks, but is also exiting earlier than usual.

“This anomaly is not only limited to December and January, but we are also observing warmer February months of late. Over the last decade, we have recorded at least five days when the temperature in Delhi in February has crossed 30°C. The trend of severe and short winters is an impact of the climate crisis and this cannot be ignored,” said Palawat.

February data shows that this time, the day time temperature has been around 4-5°C above normal across northwest India. IMD data shows that this season, the maximum temperature in February has been on the brink of touching the 30°C mark on three occasions. On February 6, the maximum temperature was 29°C, on February 9 it was 29.4°C and on February 10 it was 29.7°C.

The Met department said while some parts of north India have already started recording temperatures above 30°C during the day, others are expected to follow suit by the end of February.

Records show that February has recorded such high temperatures in the recent past. In 2021, temperature over 30°C was recorded between February 23 and 27, with the maximum temperatures peaking to 33.2°C on February 25. In 2018, too, the mercury had risen above 30°C on five occasions.